Mitchell v. Tilghman

*378 Mr. Justice CLIFFORD delivered the opinion of the court. Exclusive jurisdiction, in all actions at law aud suits in equity arising under any act of Congress granting or confirming to inventors the right to their inventions'or discoveries, is conferred upon the Circuit Court, subject to the condition that the final judgment or decree in such a con-, troversy may be removed here for re-examination. On the third of October, 1854, letters-patent were granted to the complainant for a new and useful improvement in processes for purifying fatty aud oily substances of animal and vegetable origin and which contain glycerin (glyceryl) as their base. His invention, as the patentee states, consists of a new and improved mode of treating such substances in order to produce fat-acids and solution of glycerin, which,, as be says, was not known or used before his application, and the recital of the patent is that it shall take effect from the ninth day of January preceding the date of the instrument. By virtue of the said letters-patent, as the complainant alleges in his bill of complaint, he acquired the exclusive right to make and use the described improvement, and to vend the same to others to be used; and he ^Iso alleges that the respondent, prior to the time when the bill of complaint was filed, without his license and in violation of his rights, engaged in making aud using his patented process, and that he, the respondent, intends to continue to make aud use the same, as set forth in the bill of complaint. Service, was made and the respondent appeared and filed an answer setting up séveral defences, as follows: 1. That the complainant, on the ninth of January, 1854, was not the original and first inventor of the improvement described in the said letters-patent. 2. That the result described in the specification and claims of the patent cannot be accomplished, so as to be practically useful, by the method and apparatus described in the specification. 3. That the respondent never practiced or used the patented process of the complainant as charged in the bill of complaint, or in any other manner. He admits that he is *379 engaged in manufacturing candles, and that in manufacturing such articles he uses water and steam at high temperature, and that he also uses such pressure as arises from the expansive force of hot water or steam in a close vessel, but he denies that he uses any such method, process, or appar atus as those described in the letters-patent of the complainant. 4. That the patented processes described in the specification were well known to chemists and men of science and to manufacturers long before the alleged invention of the complainant, and were also used and practiced by them and were described in printed publications before the complainant filed his application for a patent. 5. That the use of a close vessel of sufficient strength to resist the pressure of water when heated,- or any pressure needed when using water to decompose other substances, was known .to, and practiced by, meu of science and manufacturers in this country and elsewhere long before the alleged invention; that highly heated water when used as described is an elementary principle open and free to all, and that such a principle is not one that is subject to a patent; that a prior knowledge of the alleged invention was possessed by many other persons, and that the same was described in many.printed publications, as fully set forth in the answer. Issues of the kind cannot be intelligently determined without a clear understanding of the nature and scope of the invention secured by the letters-patent, as it is the patented invention which it is alleged the respondent has infringed, and in order to such an understanding it becomes necessary, as a preliminary step in the investigation, to construe and define the claims of the patent, as the most efficient means of ascertaining the precise nature and extent of the inquiry involved in the respective issues presented in the pleadings. What the patentee claims as bis invention is the process of manufacturing fat-acids and glycerin from fatty or oily substances by the action of water at a high temperature and *380 pressure, which, beyond doubt, is the true object of the invention described in the specification, as plainly appears from the' description of the means employed by the patentee to decompose the described substances and to produce the described result. His invention, as the patentee states, consists of a process to produce fat-acids and glycerin from the described fatty and oily substances by subjecting the substances to the action of water at a temperature and pressure, so high as to decompose those substances arid cause the elements of the same to combine with water, and by such means to produce fat-acids and solution of glycerin, which is the described result. Specific description is also given as to the relative quantity of water to be used, and of the character of the vessel to be employed, as means to create the high temperature and pressure and to decompose the original substances, and cause the elements of the same to combine with the water to produce the result described in the patent. Such substances, the specification states, must be mixed with a quantity of water, equal in bulk to one-third or one-half of the fatty or oily substance to be subjected to the patented process, and that the mixture of the substance and the water must be placed in some convenient vessel in which it can be heated to the melting-point of lead and be kept at that temperature until the operation is complete. Undoubtedly the mixture may be placed in any convenient vessel of sufficient strength to resist the internal pressure when the solution is heated to the point described in the specification, but it is equally clear that any vessel not strong enough to resist such a pressure would not be a convenient one for such a purpose, nor is any one of less strength within the contemplation of the patentee, as he states with emphasis that the vessel must be closed and of great strength, so that the requisite amount of pressure may be applied to prevent the conversion of the water into steam, and he might have added, to prevent the vessel from bursting. High temperature, in the view of the patentee, is indispensable, and inasmuch as the vessel must be closed it fallows that the vessel must be one of great strength, as the high tempera *381 ture will necessarily produce very great internal pressure. Hence the requirement is that the vessel must be one of great strength, and the patentee suggests, as the best mode of carrying his invention into effect, that the mixture, prepared as described, be passed through a tube or continuous channel, heated to the before-mentioned temperature, that is, to the melting-point of lead. Figures of the several parts of the described apparatus for performing the operation are given in the drawings, and the inventor proceeds to state, that in applying his process and carrying it into effect he places the fat or oil to be subjected to the process in the receiving vessel shown in the drawings, with from one-third to one-half its bulk of warm water, and to effect the described result he employs a piston with a perforated disk, arranged to work up and down, in the receiving vessel, which being kept in rapid motion will cause the fat or oil and the water to form an emulsion or intimate mechanical mixture, which is the mixture to be subjected to the high temperature and pressure. But the heat is to be applied in another vessel, as shown in the drawings, and for the purpose of removing the mixture to such other vessel the inventor employs a force-pump, like those in use for hydraulic presses, by means of which he drives the mixture into and through a long coil of very strong iron tube, which being placed in a furnace is continued there until the mixture is heated to the temperature of melting lead. Attached to the opposite end of the coil is a refrigerator or cooling apparatus, but the inventor states that he prefers that the high temperature of the mixture should be maintained for ten minutes before the product passes through that part of the coil immersed in water, by which it is cooled down from its high temperature to 210° Fahr., after which it escapes through the exit valve to the vessel prepared to receive the product of the patented process. High heat applied in the manner and by tbe means described is unquestionably the agent employed by the patentee to decompose the fatty and oily substances to be subjected to the patented process, and it is equally certain that he contemplates that the tempera *382 ture shall be so high that the fatty and oily substances, as mixed with the water, in the manner before explained, will be decomposed and converted into fat-acids and solution of glycerin in a brief space of time, not exceeding ten minutes, as he gives no intimation that it will ever be necessary to continue the mixture in the heated coil beyond that length of time. Rapid manipulation and high heat are therefore the leading characteristics of the described process, as the great pressure mentioned is only the consequence of the high heat, but as the high heat is indispensable to produce the described result, and as the vessel containing the mixture to be heated must be closed, it is quite obvious that the vessel must be one of very great strength, else it would prove to be a very inconvenient one, as it would be likely to burst. Support to that conclusion is found in the description which the inventor gives of the character of the tubes which he employs as the vessel for heating the mixture. He employs coils of tube for the purpose, arranged in such a manner that a considerable length of the same will occupy but a moderate space, the coils being kept about a quarter of an inch apart from each other. Tubes of the kind are made of iron, and the inventor states that they are one inch in the’external diameter with a half-inch bore, incased with solid cast iron, which also covers the outer coils or rows of tubes to the thickness of half or three-quarters of an inch, to insure uniformity of temperature in the different parts of the coil and to give strength to the apparatus and to protect it from injury by tire. Much additional confirmation to the conclusion that the process of the patentee contemplates high heat and rapid manipulation is also found in the other parts of the specification. Evidently the inventor is of the opinion that the operator must be exposed to imminent danger unless the vessel is one of very great strength, as he states that he deems it prudent to test the strength of the apparatus by a pressure of ten thousand pounds to the square inch before taking it into use. Such a test he deems prudent before using the vessel, but he expresses the opinion that the work *383 ing pressure necessary in using the degree of heat required will not be found to exceed two thousand p>ounds to the square inch, which admission of itself is sufficient to maintain the conclusion that high heat is the agent which the inventor in his process employs to decompose the substances subjected to the patented process. Certain substances, such as palm oil, the inventor represents, may be decomposed and converted into fat-acid and glycerin under his process when the temperature is at or below the melting-point of bismuth, but he states that the heat in decomposing such a substance may be raised considerably above the melting-point of lead without any apparent injury, and he adds that the decomposing action of the water becomes more powerful as the heat is increased. Considered as a whole these several considerations show to a demonstration, in the judgment of the court, that the invention described in the specification and embodied and claimed in the patent is the use of great heat in the manner described to decompose the described substances w'hen properly prepared, by being pulverized or broken into small particles and mixed with water, and cause the elements of the decomposed substances to unite with the particles of the heated water by which the mixture is converted into, fat-acids and solution of glycerin. Manifestly great heat, applied in the method described, is the principal agent, but water is an essential ingredient, as without it the product of decomposition would be destroyed in the operation. Evidence that the inventor contemplates that the change in the substance shall be accomplished in a brief space of time abounds in the specification. Ten minutes is the maximum time suggested that the high temperature should be maintained while the mixture is flowing through the heated tubes before it passes into the refrigerator, but the patentee also states that it is important for the quickness and perfection of the decomposition that the oil and water should continue, during the passage of the emulsion through the heating tubes, in the same state of intimate mixture as they were when the mixture was driven into the heated coil, and to that *384 end the inventor states that he prefers to place the series of heating tubes in a vertical position, so that if any partial separation takes place while the liquid passes up one tube, the change may be corrected as the liquid passes down the next. Suitable means are pointed out to indicate to the operator the state of the heat in the tubes, and for that purpose the inventor suggests the making of certain indicators or gauges showing the melting-point of certain metals and other substances, of different and known degrees of fusibility, and he gives the series which he has used, u'hich consist of tin, melting at 440° Fahr.; bismuth, 510° Fahr.; lead, 610° or 612° Fahr.; nitrate of potash, 660° Fahr.; and he describes the mode in which suen gauges may be constructed. Palm oil will be decomposed by heat at 510° Fahr., and the inventor mentions that as the lowest gauge for the treatment of any known fatty or oily substance to be subjected to the patented process under consideration. Ordinary fats, such as beef tallow, or the tallow of sheep, require the heat to be raised to 612° Fahr., which is the melting-point of lead. Mention is made in the series set forth in the specification of the melting-point of tin, which is 440° Fahr., but the mention of that chemical fact was doubtless made as a guide to the operator in carrying up the heat to the point necessary to decompose the respective substances, such as palm oil or the ordinary tallows, all of which require the heat to be raised to a point higher than the melting-point of tin. No different conclusion can be reached, as there is nothing in the record which gives any countenance to the theory that the melting-point of tin, 440° Fahr., was given as a gauge of heat which, under the process of the patentee, would decompose any known fatty or oily substance in such a manner as would enable the operator to manufacture the product described in the patent. Substances are mentioned in the specification which, under the described process, would require the heat to be raised to the melting-point of bismuth and to the melting-point of *385 lead, but the specification does not make mention of any substance of the kind which can be decomposed as required at the melting-point of tin, nor does it mention any one which for the same purpose would require the heat to be raised to the melting-point of the nitrate of potash. Probably the former was mentioned for the guidance of the operator, as before explained, and it may be that the latter was given for a corresponding purpose as the maximum limit for the operator in raising the heat to decompose such fatty and oily substances as the ordinary beef tallow or the tallow of sheep, which require the heat to be raised to the melting-point of lead in order to produce a good result under the patented process. Two other requirements of the specification support the theory that high heat is the principal agent of the patented process, and that the vessel to be used for heating the mixture must be kept closed during the process of decomposition, and be one of sufficient strength to sustain, without bursting, an internal pressure of at least two thousand pounds to the square inch. One is that the exit valve is required to be so loaded that when the heating tubes are at the desired working temperature the valve will not be opened by the internal pressure produced by the application of the heat to the mixture, so that when the pump is not in motion none of the mixture will escape at the other end of the apparatus ; and the other requirement is that “ no steam or air shall be allowed to accumulate in the tubes, and that the tubes shall be kept entirely full of the mixture.” Argument to show that the vessel used for heating the mixture must be kept closed is unnecessary, as the terms of the specification expressly require it, and the patentee to that end directs that if practicable the ends of the tubes should be welded, and if not, that they be connected by certain described joints to accomplish the same purpose, evidently regarding a compliance with the requirement that “the vessel must be closed” as an indispensable condition. Half or one-third of the mixture to be subjected to the patented process is water, and the condition set forth in the *386 specification is imperative that the vessel used for heating the mixture must be closed, that the requisite amount of pressure may be applied to prevent the water from being converted into steam; and it is also an express condition that no steam or air should be allowed to accumulate in the tubes, for reasons which will be obvious to any who will carefully examine'the described method of producing the described result. Means of a mechanical character are prescribed in the specification for intermingling the fat and the water into what is called an emulsion, which is the mixture to be subjected to the patented process, but the difference between such an intermingling of one substance with another, which may be accomplished by a stirrer or by the churning process, and the actual union produced by chemical affinity between two or more substances, is as wide as one thing well can be from another. Such an intermingling of fat with water does not work any chemical change in either substance, as it creates at best but a temporary affinity. Consequently the water, if the mixture is left for a sufficient length of time undisturbed by the stirrer or piston, will separate from the particles of fat and settle at the bottom. Widely different results flow from chemical affinity, as such an affinity will produce a new and distinct substance, uniting, it may be, the constituents or properties in whole or in part of substances as different as fat and water. Fats consist of several constituents closely united in indefinite proportions, of which olein, margarin, and stearin are the only ones usually recognized and defined by chemists; the former constituting the oily and the two’ latter the solid principle of the united substance. * These constituents or elements are held together by chemical affinity, the consistency of the united substance depending upon the respective proportions of the constituent parts. High heat will overcome the affinity by which the constituents are united and decompose the substance. Different *387 kinds of fat, however, require different degrees of heat to effect the decomposition of the united substance, varying in intensity from 510° Fahr., the melting-point of bismuth, to 610° or 612° Fahr., the melting-point of lead, which are the very temperatures mentioned as required in the specification of the complainant’s patent. But it should be remarked in this connection that the decomposition of such a substance by heat alone will not produce fat-acids or solution of glycerin. * Free fat-acids and solution of glycerin are what the patentee promises as the result of a proper application of the patented process. Those acids, it is conceded, are oleate, margarate, and stearate, which, it is claimed, the process will produce, together with the solution of glycerin, but it is clear that heat alone will not produce either of those fat-acids or the solution of glycerin, as the three acids and the glycerin are chemically combined in the original substance with the oxide of glyceryl as an acidifying base. Temperatures such as described will decompose the fat, but unless some chemical agent, such as water, lime, soda or potash, is present to take the place of the oxide of glyceryl to acidify the olein, the margarin, and the stearin, or to oxidize the said several constituents and to convert the same into oxide of olein, margarin, and' stearin, neither of the fat-acids required, to wit, oleate, margarate, or stearate, can be obtained from the decomposition of fats by heat, as the oxide of glyceryl, which was their báse in the original substance, is separated by the act of decomposition; nor is it possible, unless water or its equivalent be present when decomposition takes place, to obtain solution of glycerin, for reasons equally conclusive though somewhat dissimilar in the chemical sense, as the presence of water or its equivalent is required in the latter case to hydrate the glyceryl and convert the same into the solution of glycerin. Without the presence of water or its equivalent constituents neither the fat-acids mentioned nor solution of glycerin will be obtained *388 by beat, but with it the three fat-acids mentioned and solution of glyeeriu will be produced if the operator complies with all the other conditions described in the specification. * Viewed in the light of- these suggestions, as the question should be, it is quite clear that the two conditions last named, to wit, that the heating vessel must be kept entirely full of the mixture ahd that no steam or air must-be allowed to accumulate in the vessel employed to impart the heat, are material and indispensable conditions of the patented method of producing fat-acids and solution of glycerin .from the described substances, as without a compliance with those requirements there might not, and probably would not, be present when decomposition takes place any equivalent of a base to take the place of the oxide of glyceryl and to unite with the olein,.margarin, and stearin to convert the same into the three fat-acids known as oleate,. margarate, and stearate. These three constituents in the fat, to wit, olein, margarin, and stearin, are combined with the oxide of gtyceryl as a base, and when decomposition is effected under the influence of heat, some chemical agent, such as water or its equivalent must be present, which can take the place of the oxide of glyceryl to change the three constituents of fat just named into the oxides of olein, of margarin, and oí stearin. † Some chemical agent must also be present to take the place of the constituent which was combined with the glyceryl to produce the solution of glycerin, as represented in the specification ; and it does not appear to be controverted that in all methods heretofore practiced water or its equivalent has always been present for such purpose, and it is manifest that the requirement that water or its equivalent shall be present to accomplish that purpose, in the specification, is an indispensable condition, as the new substance would otherwise be destroyed by the operation, which requirement cannot be fulfilled unless the vessel is kept *389 entirely full of the mixture, as otherwise steam and air will accumulate and fill the vacuum. Water must be present in the mixture to furnish the requisite constituent to unite with the olein, margarin,and stearin, and to oxidize the same,-else it will be impossible to obtain the described fat-acids; and the presence of water in the mixture when the decomposition takes place is also equally indispensable to furnish the requisite constituent to take the place of the oxide evolved by the operation from the glyceryl and to unite with the other constituents of the same to produce solution of glyeerin, which the specification alleges is one of the results to be obtained from the decomposition in the method therein described.- Unless water or its equivalent be present to furnish such constituent to take tbe place of the oxide evolved from the glyceryl, the same heat that separates the glyceryl from the other constituents of the fat in the mixture will convert the same into acrolein, which is an offensive substance destitute of any useful quality, or, inf other words, the glyceryl will be converted into a substance which is neither new nor useful, and of course the process to obtain it would not be the proper subject of a patent. * Nothing provided in the patent or suggested by the patentee will secure the presence of-water when decomposition takes place, unless the vessel be closed and be kept entirely full of the mixture, as otherwise the water will be converted into steam, and steam and air will accumulate in the heating vessel. No means are described or suggested to add water to the mixture after-the mixture-is forced into the heating vessel, and it- is plain that nothing of the kind can be successfully accomplished without some material change in the apparatus. Beyond all doubt the conditions-mentioned appertain to the described method patented by the complainant for producing fat-acids and solution of glycerin from fatty and oily substances of animal and vegetable origin, which contain *390 glyceryl as their base, but i.t is equally clear that the patentee does not claim the described apparatus as auy part of bis invention, and that he is not the original and first inventor or discoverer of the scientific truth that such fats as beef tallow and palm oil may be decomposed by heat or by heat and water combined, nor of the scientific truth that fat-acids of commercial value may be obtained from such substances as tallow and palm oil by means of heat or by heat and water. Power to issue letters-patent is conferred upon the commissioner of patents, and inasmuch as such grants are executed by public authority and in pursuance of an act of Congress, the rule is that the patent, when introduced in evidence by the complaining party in a suit for infringement, affords a primd facie presumption that the patentee is the original and first inventor of what is therein described and claimed as his invention. Application for a patent is required to be made to the commissioner appointed under authority of law, and inasmuch as that officer is empowered to decide upon the merits of the application, his decision in granting the patent is presumed to be correct. * Sufficient has already been remarked to show what the alleged invention is as construed and defined by the court. Having ascertained that matter, the next inquiry is,.whether the complainant is the original qnd first inventor of the improvement? 1. Persons seeking redress for the unlawfufuse of patented inventions must allege and prove that they are the original and first inventors of the same, and that the party defendant is guilty of the alleged infringement. In the first place, the burden to establish both of those allegations is upon the party instituting the suit, but the rule, as before explained, is that where the complainant or plaintiff’ introduces the patent in evidence, if it is in due form, it affords a primd facie presumption of its correctness, which, in the absence *391 of opposing proof, will entitle the complaining party to relief. Availing himself of that rule the complainant introduced his patent in evidence, which is sufficient to show that he is the original and first inventor of his improvement, as construed aud defined by the court, unless sufficient evidence to overcome that presumption and to establish the contrary allegation of the answer is exhibited in the record. * Whether tested by the language of the claim or by that of the patent, or by the language embodied in the two introductory sentences of the specification, it is equally clear that the patentee, at the time the patent was granted, did not pretend that he was the original and first.inventor or discoverer of the scientific truth that high heat or water heated to a high temperature would decompose such fatty and oily substances as those mentioned in the specification of his patent, and the evidence in the record shows that such a pretence, if it had been made, could not have been supported for a moment. Opposed to that proposition it is suggested that the patentee claims “the manufacturing of fat-acids and glycerin from fatty substances by the action of water at a high temperature and pressure,” which must be admitted subject to the universal qualification that the legal construction of every such claim is that the patentee means to limit the same to his described method or process; or, if it be a machine, to his described means of obtaining or of accomplishing the described result. Usually the claim contains the words as described or substantially as described, or words of like import, which are everywhere understood as referring back to the descriptive parts of the specification. Words of such import, if uot expressed in the claim, must be implied, else the patent in many cases would be invalid as covering a mere fuuction, principle, or result, which is obviously forbidden by the patent law, as it would close the door to all subsequent improvements. † *392 Doubtless, an invention may be good though the subject of it consists in the discovery of some principle of science or property of matter, never before known or used, by which some new and useful result is obtained, and such an invention or discovery may be the subject of a valid patent without including in the claim any new arrangement of machinery to accomplish the object, provided the inventor describes, as required .in the patent law, the method, process, or means of applying the invention to practical use and of obtaining the described new and useful result. * Limited, as explained by reference back-to the descriptive parts of the specification, the claim may well be regarded as in due form, but it is quite clear that it would be invalid if, it is not so limited, as it has always been held that a patent embraces nothing more than the improvement described- and claimed as new, and that any one who afterwards discovers a method of accomplishing the same object, substantially and essentially differing from the one described, has a right to use it and to vend it to others to be used. † Apply that rule and it is clear that the invention must be limited to the described method of producing free fat-acids and solution of glycerin .from the fatty and oily substances therein mentioned, as the patent states that the patentee alleges that he has invented a new and useful improvement in processes for purifying such fatty and oily substances, and the opening sentence of the specification describes the invention as a new and improved mode of treating fatty and oily substances, and the patentee, in describing his invention, states that it consists of a process for producing free-fat-acids and solution of glycerin from such fatty and oily substances as are therein particularly described, and.there is not a word either in the specification or claim of the patent to warrant the conclusion that the patentee or the commissioner of patents, at the time the patent was granted, regarded the patentee as the original and first inventor or discoverer of *393 tbe scientific truth that such fatty and oily substances may be decomposed by high heat or water heated to a high temperature. Unquestionably the method or process embodied in the patent includes high heat and rapid manipulation, but the patentee is not the original and first inveutor of the scientific truth that heat or water at high temperature will decompose such fatty and oily substances as those mentioned in the specification. Different gauges of heat to be employed in applying his process are certainly given in the specification, as before expláined, but it is a great mistake to suppose that the gauge for decomposing such fats as beef tallow or the tallow of sheep admits of any variation except what is authorized by the word “about,”, or that the gauge given for decomposing palm oil may be varied from the melting-point of bismuth, except so far as the authority to diminish the temperature may be inferred from the words “at or below,” which words, when properly construed, mean substantially the same thing as the word about, when the latter is used to qualify tbe temperature designated as the melting-point of lead. Attempt is made in argument to show that the-respective gauges given in the specification to specify the required degree of heat are subject to a much wider variation, and that the patentee did not intend to require that the mixture-should be exposed to any higher temperature than that which should prove to be requisite to accomplish the described result.. Suppose that could be admitted, still it is not probable that the admission would much vary the case if the apparatus employed should not be changed, and all the conditions for applying the process-should remain in full force, as rapid manipulation is an express condition in applying the process of decomposition, which, it is believed, cannot be accomplished in the time allowed.unless the high temperature is maintained. Support to the theory that the gauges, given-admit of a wider variation than is here supposed is attempted to be drawn from the sentence in the specification which im *394 mediately follows the statement that the decomposition of the water becomes more powerful as the hetjt is increased. Fatty matters such as palm oil, says the patentee, may be changed into fat-acids and glycerin at or below the melting point of bismuth, but he states in the same connection that the heat in such a case has been carried considerably above the melting-point of lead without any apparent injury; and he adds that the decomposing action of water becomes more powerful as the heat is increased. Then follows the sentence which is invoked as supporting the theory that the gauges of heat given in the specification, to wit, the melting-point of bismuth and the melting-point of lea.d, are subject to indefinite variation. By starting the apparatus at a low heat, says the patentee, and gradually increasing it, the temperature giving products most suitable to the intended application of the fatty substance employed, can easily be determined. Evidently the sentence should be examined in the light of the context, and when so examined it is quite clear that the patentee never intended to employ the language in any such sense as that which the complainant ascribes to it, as he was speaking of palm oil, which is decomposed at the melting-point of bismuth, and had just remarked that the heat, in applying the process to that substance, had been carried considerably above the melting-point of lead without any apparent injuryWater, said the patentee, becomes more powerful to decompose such substances as the heat is increased, and then adds, as a precaution to the operator, not to carr}- it too high above the gauges given; You can easilj' determine what is best in any given case by starting the apparatus at a low heat and gradually increasing it to the gauge given or above, as may appear to be best from the particular substance subjected to the process and the quality of the product obtained by the operation. Not an intimation Í3 given in the sentence that any less heat will accomplish the purpose than that indicated by the gauges mentioned in the specification. On the contrary, the language employed, if it *395 warrants iiuysubstaiitia! variation from the prescribed gauges, justifies the inference that the heat may be increased above the temperatures mentioned rather than diminished. High temperature and pressure are among the leading characteristics of the invention, as appears from the claim and every part of the specification. Doubtful expressions may be subject to construction, but where the language employed is clear and unambiguous it must speak its own construction in the specification of a patent as well as in any other grant issued by public authority. Intention in every case, it may be'admitted, is the primary rule of construction, but language invoked to support a particular theory must be such as is fit, when it is compared with the whole instrument, to express the imputed intention, else the theory in question cannot be supported, as courts of justice cannot legislate nor can they add to a grant or contract any stipulation or condition which it does not contain. Consequently, the theory of the complainant that the sentence under consideration warrants the conclusion that the claim of the patent includes low as well as high heat must be overruled. * Additional observations respecting the apparatus employed by the patentee are unnecessary, as he expressly states that he does not intend to claim it as any part of his invention. Enough has already been remarked also to show what is the nature aud scope of the invention and to point out what the question is which is involved in the first issue presented in the pleadings. Construed and defined as explained, the first issue inspecting the patent must be fouud for the complainant, as the proofs in the record bearing upon the question of novelty are not sufficient to overcome the primd facie presumption that the patentee is the original and first inventor of what is described in the patent as his invention. † 2. Graut all that, still it is insisted by the respondent that *396 the result described in the specification and claim of the patent cannot be accomplished so as to be practically useful by the method and apparatus described in the specification. Whoever discovers that a certain useful result will be produced in any art, machine, manufacture, or composition of matter by the use of certain means is entitled to a patent for his invention, provided he specifies the means he uses in a manner so full and exact that any one skilled in'the science to which it appertains can, by using the means he specifies, without any addition to or subtraction from the described means, produce precisely the result he describes. Such description must .be correct, as it is settled law that the'patent is void if the described result cannot be obtained by the described means. * Nor does it make any difference whether the effect is produced by-mechanical principles or by chemical agency or by the application of discoveries in natural science,-as in either case the-requirement-of the act of Congress is imperative that the patentee must describe the method, process, or means he employs in full, clear, and exact terms, and the end which the iuventiomaccomplishes. Inventions, in order that they may be the proper subjects of letters-patent, must be new and useful. Utility in most cases is a question of fact, as it usually depends upon the evidence resulting from actual experiment.' There are two modes, says Mr.-Curtis, in which the utility of an invention may be impeached,-the second of which is where it appears that it is mott capable-of being used to effeet the object proposed, which is theiquestion presented in the-second defence set up by the respondent. † Cases arise also, even where the means .described, will ac complish the described- result, when it cannot be held that the invention is useful if it appears that the operater, in using the described means, is constantly exposed to imminent danger, either from the explosive tendency of the sub *397 stance to be used or from the liability of the vessel to burst which is required to be employed as means of accomplishing the patented result. Where the patentee finds it necessary to employ any such dangerous means to accomplish the described end it cannot be held that his invention is useful, within the meaning of the patent law, even though it appears that the operator, when no such disaster happens, may be able to work out the described result by the described means, as it is quite clear that Congress, in making provision to secure to inventors the exclusive right to their discoveries, never intended to promote any such as were in their nature constantly dangerous to the operator in employing the described means to accomplish the described result. * Apply these rules and it follows that neither an invention which will not enable the operator to accomplish the described result nor one which constantly exposes the operator to the loss of his life or to great bodily harm can be regarded as useful within the meaning of the patent law. Patents were granted to the supposed inventor by the proper public authorities in England, Prance, and Belgium, as well as by the proper public authorities in the United States, but the respondent insists that the described result cannot be obtained by the means and in the mode of operation described in the specification, and that the invention has never been reduced to practice by the use of those means or in that mode of operation, either in the United States or in any one of the foreign countries where the same has been patented. Both branches of the proposition are controverted by tbe complainant and many depositions and other proofs upon the subject were introduced at the hearing. Witnesses were examined by the complainant to prove the affirmative of the issue, but none of them appear to sustain his views in that behalf unless the scope of the invention is extended beyond the means and mode of operation described in the specification as construed and defined by the court. Proofs *398 of the kind, if they exist, could easily have been procured, as both the complainant and his brother, who acted as his agent in efforts to introduce the invention in the United States, were examined as witnesses in the case. Licenses were given by the complainant in some instances, and he called Charles T. Jones, one of his licensees, to prove the affirmative of the issue under consideration. It appears by his deposition * that he became a member of a certain firm in 1849, and that the firm were engaged in the manufacture of candles; that they first used the process of saponification with about fourteen per cent, of lime in an open vessel; that they decomposed the lime soap thus obtained by sulphuric acid, using for that purpose two and a half pounds of sulphuric acid to each pound of lime; that they continued to use that process until the fall of 1859, when they introduced the process of saponification under pressure of about one hundred and thirty pounds to the square inch, with only six or seven per cent, of lime and with a corresponding diminution of sulphuric acid. Subsequently they abandoned the second process used by them and introduced another, which the witness calls the process of the complainant. On cross-examination he was asked whether water was not used in their first process and whether he ever knew any process by which fats were decomposed into fat-acids and a solution of glycerin without the intervention of water; to which he answered, water was used in the first process described, but in quantities only slightly in excess of that requisite for preparing the milk of lime; and he added that he did not know that the decomposition of neutral fats into fat-acids and a solution of glycerin had ever been accomplished without the intervention of water. Counsel for the respondent also requested the witness to describe the process used by his firm which he calls^ the complainant’s process. His answer is, in substance and effect, as follows: He places the melted fat to be treated in a lar<re vessel with a quantity of water equal at least to *399 one-half the bulk or weight of the fat., and subjects the melted fat and water to a steam pressure of three hundred pounds to the square inch for a period of about five hours, keeping the water and fat in intimate contact by pumping the water from the bottom to the top of the vessel and discharging it on the upper surface of the fat, in order that the water may make its way to the bottom of the same; to which he added that he preferred to use half of one per cent, of lime, for the reason, as he states, that that quantity of alkali enables him to perfect the decomposition in four hours at a pressure of two hundred and fifty pounds to the square inch with material economy of fuel and of wear and tear of machinery; and he states that since ascertaining the advantages of the lime he has adhered to that mode of operation. Responsive to another question he states that the apparatus was first put in operation, under the superintendence of the complainant, in September, 1863; that the vessel used was manufactured in Philadelphia; that it comprises a tube thirty-eight feet in length and thirty-eight inches in the internal diameter; that it is made of iron plates of the thickness of a half inch, and a copper, tube of nearly the same length, thirty-five inches in diameter, which is placed inside of the iron tube so as to leave an annular space of about one and a half inches between the copper and the iron vessel, whose estimated capacity is about ten thousand pounds of oil and water, but the quantity of fat usually put into the vessel at one time is about six thousand pounds, with about four thousand pounds of water, all of which is placed in the copper vessel, which serves to fill the vessel within three feet of the head or top; and he states that when the decomposition is perfected the water holding the glycerin in solution and the fat-acids are discharged into their respective receptacles. Two vessels are used instead of one, as directed in the specification, because iron is cheaper than copper, and to secure greater strength to resist the requisite pressure aud to save the iron from contact with the fat-acids, which dis *400 colors the product and rapidly corrodes the iron to such an extent that it will soon render the vessel unfit for use. Satisfactory products, as the witness states, may be obtained by the process without lime, though he adheres to the statement that he prefers to use it in order to diminish the pressure which would otherwise be required, and for the economy which it effects in fuel, labor, and time, but he states without any qualification that no one in their manufactory ever mixed any fatty or oily substance with water, in the proportions given in the complainant’s specification, and placed the mixture in any vessel in which it could be heated to the melting-point of lead until the operation was completed and thereby obtain free fat-acids and.solution of glycerin. Even without any discussion it is obvious that the means and mode of operation -practiced by the witness are widely different from the method or process described in the specification of the complainant’s patent. Instead of working in a vessel entirely full of the fat and water and under a pressure sufficient to prevent the presence of steam, the operation under the process of the witness is performed in a vessel only partly filled, which is opeu at the upper end and inclosed in another vessel, and the heat is applied by the introduction of steam from boilers outside. Other differences also exist, as for example, instead of being worked at a temperature of 510° or 612° Eahr., and in a vessel capable of sustaining an internal pressure of two thousand pounds to the square inch, the process of the witness is worked at a temperature represented by a pressure of only three hundred pounds to the square inch, which is a latitude of deviation not warranted by any language to be found in the complainant’s specification. Two other differences may also be mentioned, which are equally persuasive, to show that the method or process practiced by the witness is substantially different from that embodied in the patent of the complainant. Instead of the fat and the water being maintained during the eutire operation in a state of intimate mechanical mixture, as required *401 in the specification, a pump is provided, not to force the mixture into the heating vessel, but to be kept constantly at work to draw the water from the bottom of the vessel and to discharge it on top of the charge of fat, in order that it may percolate down through the fat and supply the deficiency occasioned by the fact that the ■water is constantly being converted into steam. Ten minutes is the maximum time allowed for the operation in the complainant’s specification, but the method or process employed by the witness, instead of effecting the decomposition' in ten minutes, requires at least four or five ■hours, even when he uses a small proportion of lime to assist the chemical action of the heated water. Besides the differences between the two methods already pointed out, there are others which may be suggested, equally striking and of a character equally persuasive, to show that the two methods are. substantially different, as for example, the apparatus employed by the witness consists of two vertical cylinders, one within another, instead of a coil of tubing, with an annular space between the two, as before explained, of an inch and a half. Fat and water in nearly equal proportions are charged into the inner cylinder, leaving a vacant space at the top of the same of about three feet. Like the coil of tube the outer cylinder is steam-tight, but the inner one is open at the top. Steam for the operation is generated in two separate boilers, which is introduced through the top of the outer cylinder to the space between the two and through the upper end of the inner one, which is open, to facilitate the circulation of the steam, in order that the fat and water iu the inner cylinder may be heated to the temperature represented by a pressure of two hundred and fifty to three hundred pounds to the square inch; and the witness testified that he regarded the use of the pump and the use of some lime as essential to the use of the apparatus with the greatest economy. Licensees of the complainant were also examined by the *402 respondent, to wit: Nathaniel Ropes and Nathaniel Ropes, Jr. * These witnesses have had great experience in manufacturing caudles, and they testify that they know of no place in this eouutry where candles or soap are manufactured from free fat-acids produced by water alone at high temperature and pressure without the use of alkali. They both describe the old saponifying process as consisting in the treatment of fat by water heated in an open vessel, lime being mixed with the water, by which the glycerin was separated from the other constituents of the fat, leaving what some manufactures call lime soap, or fat-acids and lime, which latter ingredient was afterwards removed by sulphuric acid, the residuum being free fat-acids. Changes were made in their mode of operation early in the year 1860, which alterations were introduced to them by the brother of the complainant, who experimented in their manufactory several months before he put the apparatus adopted in operation. By that plan they use water in equal proportions with the fat, with a half per cent, of lime aud double that quantity of sulphuric acid, the whole being heated to a temperature representing a pressure of about one hundred and fifty pounds to the square inch in a closed vessel for twelve hours. Formerly they conducted the operation in open tubs, using thirteen per cent, of lime with double that quantity of sulphuric acid, but since the new method was introduced by the agent of the complainant they have substituted closed copper tanks in the place of the open tubs, using, however, the same agents to effect the decomposition of the fatty substances, though in different proportions. Copper tanks are used as receptacles for the fat and the water, but the steam to communicate the heat is generated in a large iron boiler thirty feet in length aud forty inches in diameter, with which the copper tank is connected by means of steam pipes furnished with stop-cocks as regulators in the use of the steam. There is also a shaft in the *403 tank having radial arms, which shaft is kept in rotation to cause and preserve an iutimate mechanical mixture of the fat and the water during the whole operation. Instead of having the tank constantly filled with the fat and water the fact is that it is never filled, nor is the mixture kept under a pressure sufficient to prevent the accumulation of steam and air, as directed in the specification of the patent described in the bill of complaint. Empty space is left in the tank above the fat and water at the outset sufficient to allow boiling, which space of course would be filled with steam and air. Heat is communicated to the mixture by introducing steam from the large iron boiler into the copper tank, creating a temperature causing a pressure of one hundred and fifty pounds to the square inch. Several months were employed in making the experiments before the method now in use was finally put in practice by the complainant’s agent. He tried it without lime at a pressure of two hundred pounds, allowing twenty-four hours for the operation, but the result was not satisfactory. Dismissing that method he next tried the experiment with fat and water in the proportion of two to oue, allowing twenty hours; still the result was unsatisfactory. Next he tried the compound of fat and water in equal proportions, using only half of the water during the first part of the operation, then discharging that and putting into the charge the other half of the water, and he found that the operation produced a good result in twelve hours. Some of the experiments were without lime, but the witnesses state that inasmuch as they found that by the addition of lime they could accomplish the work at a pressure of one hundred and fifty pounds to the square inch and in less time, they have ever since continued the use of lime in their business. Much discussion of the process introduced on that occasion is unnecessary, as it appears that instead of working at a heat equal to the melting-point of lead, in a vessel capable of sustaining an internal pressure of two thousand pounds, these licensees of the complainant use a certain per cent, of lime at a pressure not much above one hundred and fifty *404 pounds; and it appears that they decompose the fat in a vessel not filled with the mixture, nor provided with a mechanical stirrer, and leave a vacant space in the vessel sufficient for circulation, in which steam is not only generated but is introduced from a separate boiler. Differences such as these require no comment except to say that the method is entirely different from that described in the patent in question, and to add that it corresponds much more nearly to the method described in a patent dated May 15th, 1860, subsequently obtained by the complainant, and which was introduced in evidence by the respondent. Reasons exist besides those disclosed in the testimony of those witnesses to support the conclusion that the complainant never supposed that his patent conferred the exclusive right to use temperatures and pressure to decompose fats with water alone much below the gauges given in his specification, and that he had cometo doubt, several years before those experiments were made, whether the patented method or process could be accomplished so as to be practically useful by the meáns and in the mode of operation pointed out in the patent. His letter, dated London, June 25th, 1856, addressed to a certain firm in Cincinnati, * affords strong support to that conclusion, in which he states that our experiments in the factories here and in Paris have shown that on the large scale the decomposition of fats by water is more conveniently effected by modifying the apparatus originally proposed so that the fat and water are exposed to a comparatively lower heat and pressure for a longer time, instead of a very high pressure for a few minutes. By which means he suggests in the same letter that a considerable quantity of material may be treated at one charge in an ordinary steam-boiler lined with lead or copper, and may be provided with an agitator in the place of .using the continuously working pump and coil of pipe, and the suggestion is that *405 at a pressure of two hundred and twenty-five pounds to the square inch tallow, palm oil, or lard stearin may be completely decomposed in five hours. Nearly two years before the date of that letter, to wit, on the twenty-fifth of March, 1854, the complainant took out a patent in England for the same invention as that described in the patent in issue in this case, and the proofs show that he made various efforts to introduce it into practice in that country. He remaiued there, it seems, from 3854 to 1859, and it appears that in June, 1854, he exhibited his process in the old form to George F. Wilson, the managing director of the Price Patent Candle Company, and the company entered into a contract with the complainant respecting the same, by which he assigned the said letters-pateut and the privileges thereby granted to the said company, and that the said company, in consideration of the assignment, covenanted to pay him an annuity of one thousand pounds sterling from the month of October of the following year during the continuance of the patent, subject to various conditions, and among others to be terminated by giving notice to the complainant as therein provided; the company were also to have the use of several other patents therein described, which have since expired. Proofs were also exhibited showing that the said company have ever since paid the stipulated annuity, but there is no satisfactory evidence in the case to show that they have ever applied the process to produce fat-acids and solution of glycerin by the means and in the mode of operation described in the specification, as construed and defined by this court. Some use, it may be presumed, has been made of the patent by the assignees, but what that use is does not very satisfactorily appear. It does appear, however, from a paper read before the British Association, in September, 1855, by the general director of the company, to whom the complaiuant testifies that he exhibited his process the year previous, that he stated that in our new process the only chemical agents employed for decomposing the neutral fat and for separating its glycerin are steam and heat, and that *406 the only' agents used in purifying the glycerin thus obtained are heat and steam. * Strong confirmation of that is also derived from a paper read by the same person at a session of the Society of Arts, held in that country, January 25th, 1856, also put in evidence by the complainant, † in which the author says, in speaking of the patented process, “It'has yet to be proved how far it can compete successfully with distillation,” adding that they had made an arrangement with the inventor which, as he expresses himself, will give them the means of testing its commercial merits, and then he proceeds to state that on witnessing a trial of the process in the small tube apparatus, it struck him that steam passed into the fat at a high temperature should effect by a gentle process what the patentee aimed at effecting by a violent process, to wit, the resolving of the neutral fat into glycerin and fat-acids; finally stating that they had proved that the fact was so and that the glycerin distilled over with the fat-acids though it was no longer combined with those products, evidently showing that the process employed by them was at that time widely different from that claimed by the complainant. Application for a patent was also made by the complainant to the proper authorities of France during the same year, and it appears that the application was successful, as he immediately commenced negotiations through his patent agent with the firm of Monier & Co., doing business near Paris in that empire, for the sale of the patent, which negotiations resulted in a contract of sale. Pursuant to that contract he transferred the patent to that firm subject to the condition that the process would effect the results promised by the grantor. Numerous experiments were subsequently made under the superintendence of the patentee or his brother, for a period of six months, all of which produced results which the evidence shows were entirely useless. They were made iu the first place, as the senior partner of the firm states, ‡ *407 by means of a small, apparatus brought from London by the patentee, which consisted of a hollow iron tube of serpentine form, incased in a cast-iron block from which the two ends of the tube projected — one for receiving the fatty substance used in the experiments for decomposing the same, aud the other for discharging the product. • High heat was required for the purpose, and with that view the apparatus was so placed in a furnace constructed of fire-proof bricks that it received all the heat, the flames of which completely enveloped it, and which brought it to an excessive heat, but the witness cannot give the degree of heat, as the apparatus did not contain any gauge to indicate its intensity. Fatty matter and water were put in a vessel prepared for the purpose, which was provided with a bronze suction aud force pump worked by hand, and connected with one end of the iron coil projecting from the cast-iron block, by which the mixture of fatty matter and water was drawn from the receptacle aud was forced into and through the iron coil of tube, as the same was incased in the iron block, aud out at the opposite end of the same, where it was discharged into another receptacle prepared for the purpose. By means of the furnace the iron tube and the block in which the coil was incased were “ heated to an excessive degree,” estimated by the witness to exceed 500° Fabr. with an estimated pressure of more than twenty atmospheres. Both the patentee and his brother worked at the experiments ten ór fifteen days, but the decomposition of the fatty matter, as the witness states, was never complete, and that they never produced fat-acids and glycerin, the product being only an altered fatty matter, which, when washed, showed acrolein to such an extent as to fatigue the workmen who assisted at the experiments. Fifteen of the experiments were made by the patentee aided by two workmen, in the presence of the witness, and he states, without qualification, that none of the experiments succeeded. Three new apparatuses were subsequently constructed by the brother of the patentee, acting as his agent. Two were *408 constructed in Paris and one in London. Experiments were subsequently made by the brother of the patentee, and in some instances without any regard to the patented process, the aim being to find out if possible the means of overcoming the difficulties manifested in the prior attempts to produce the promised results. None of his efforts, however, succeeded, though the experiments were continued until the expenditure exceeded’ forty thousand francs, and it appearing that fat-acids and glycerin could not be produced by the process, the contract was annulled, and the witness affirms that it is impossible to decompose fatty matter and obtain fat-acids and. glycerin by the method’indicated in the complainant’s patent. He admits, however, that his firm were subsequently induced, on the return of the patentee to that country, to join with another firm engaged in manufacturing candles, to make a new contract with the same party upon the same basis as the first contract, it being represented that the patentee would introduce- a new process, based upon the principles of the patented method, which promised certain success and admirable results. Such a contract was accordingly made, and new experiments were prosecuted for a period of two or three months, but, like the first efforts in that direction, the experiments failed to produce either fat-acids or glycerin. How much these last experiments cost, the witness does not state, but he does state that the experiments were productive of no good, as they produced neither fat-acids nor glycerin. Remarks respecting the Belgium patent are unnecessary, as no proof was offered to show that the process was ever introduced into practice in that country. Having failed to accomplish such results in those countries as would show that his process would be practically useful if applied by the means and in the mode of operation described in the specification, and probably having become convinced that the decomposition of fats by water could be more conveniently effected by modifying the described apparatus so that the fat and water would be exposed to a lower *409 heat and pressure for a longer time, as expressed in his letter of the twenty-fifth of June, 1856, the patentee left England in August or September, 1859, and returned to the United States. . Conclusive proof that the patentee did not accomplish results in France, which would show that the patented process, applied by the means and in the mode of operation set forth in the specification, is exhibited in the record of the other case between the same parties, which was heard at the same time. Reference is made to the report of the jury upon organic chemistrj’ made the third of December, 1855, to the international exhibition held in Paris, which is made an exhibit in that case. Chemists, say the jury, liken neutral fats to compound ether, which was the hypothesis put forth by Chevreul in his investigations of such matters. Ether, it was known, may be decomposed by being heated to a high temperature in close vessels with water, and from that persons were led quite naturally to attempt to effect in the same way the decomposition of neutral fats, and they state that experience has confirmed the assumed theory, which, as the jury say, is the origin of all the new processes of saponification to which they refer, and they add that it was the patentee in this case who first had the idea of applying such reaction on a large scale, which they verify by an extract from the specification of the patent; * but, as they report, they visited the manufactory of Monier & Co., where they had the opportunity of seeing the trial of the process in its application to palm oil, and they conclude their report upon the subject as follows: † “ We are sorry to say that the fatty matter on coming out of the apparatus was not at all deodorized, and, more besides than that, that it gave out a strong odor of acrolein. From the point of view of the quality of the products, this arrangement of apparatus, then, by no means realized the end which the author has proposed. Moreover, in our opinion, the *410 chances of deterioration of a system of apparatus of any kind which works constantly at a temperature capable of exerting a pressure of ninety to one hundred atmospheres are such that it is hardly possible that industry will utilize it, even if the products which it furnishes were irreproachable.” Made public, as the report was, more than two years before the patentee returned to the United States, it may be presumed that it came to his knowledge before his return. On the fifteenth of May, 1860, the new patent referred to was granted to him in this country, * which affords the most conclusive proof that the alleged invention is one of a very different character from that described in the specification of the patent in issue in this case, and yet he states under oath that he verily believes that he is the original and first inventor of the improvement, and that to the best of his knowledge and belief it had not been known or used before his application for the patent, which is utterly repugnant to the pretence that anything which is embodied in that patent was included in the one granted to him more than five years before the latter application was filed. Experience seems to have greatly modified the views of the patentee, as he now characterizes the improvement as a new and improved method of decomposing fatty and oily substances, and alleges that it is applicable either when water alone is used, or when, in addition to water, a portion of alkali is used to aid the chemical action; and he also alleges, that to extract the whole of the glycerin from the fat with a moderate quantity of water, wheu the lower range of pressure is used, requires considerable time; and he actually states that his invention consists in applying the water to the fat in several successive portious. High temperature and pressure are represented as the agents of decomposition, but in the view of the complainant as expressed in that specification the high temperature required may be only that which is represented by a pressure of one hundred and twenty to one huudred and fifty pounds to the *411 square inch. Gauges to indicate the required temperature are dropped, and all idea of rapid manipulation seems to be discarded as the terms “a considerable time” or “from two to three hours” are substituted iu the place of “ten minutes.” Vessels of very great strength are no longer required, as the patentee states that his invention may be applied to any of the different forms of boilers or tanks used for the decomposition of fats by water at a high temperature or pressure, meaning, doubtless, that the terms high temperature and pressure shall be understood iu the same sense in which he employs them in a subsequent part of the same paragraph. Water may be supplied when wanted, and, of course, it is of no moment even if some of it is converted into steam; nor does the specification contain any requirement that the heating apparatus shall be kept entirely full of the mixture, or that neither steam nor air shall accumulate therein during the time required for decomposition, or, in other words,-the old specification is divested of every one of its extreme conditions, and the inventor, under his new patent, is left free to claim every means and every mode of operation which the ingenuity of man ever did or ever can invent or discover. Further remarks respecting it, however, may be omitted, as it is not the subject of litigation in this case. Chemical and mechanical experts were examined as witnesses on both sides iu about equal numbers. Those called by the complainant express the opinion that the patented process may be applied by the means and in the mode of operation described in the specification so as to accomplish useful results, and of a character to give commercial value to the new product. On the other hand, those examined by the respondent express opinions widely different, and most or all of them are of the opinion not only that the means and mode of operation described in the patent cannot be so applied that the invention will be practically useful, but several of them state that the attempt to apply it without the exercise of extraordinary precautions must be attended with danger to the operator. *412 Most of the expert witnesses made experiments in applying the process, and in the course of their examination were required to state the results of the same as supporting their opinions, but experiments made, as most of these were, with small apparatuses admitting only a small charge of the fatty substance or mixture to be treated are not entitled to much weight in determining such an issue, however satisfactory the analysis may have been to the chemist who conducted it, as the. issue necessarily involves very difficult questions of mechanics as well as of chemistry. Taken as a whole the evidence convinces the court that the patentee never did succeed in introducing his invention-into practical use by the means and in the mode of operation described in the specification to such an extent as would warrant the court in finding that issue in his favor. Doubts of a very serious character are also entertained by the court whether the patented process, unless divested of its extreme and unparalleled conditions, can ever be reduced to practice by the means and in the mode of operation described in the specification, so as to be practically useful or safe to the operator, but the proofs are very conflicting upon the point, and inasmuch as it is impossible to foresee what future experiments may do in the way of overcoming the existing (loubts and difficulties, the courtis not inclined to rest their decision entirely upon that ground. 3. Passing from that, the next question is whether the proofs show that the respondent practiced and used the patented process of the complainant, when properly construed and defined, as charged in the bill of complaint. Such an inquiry cannot be intelligently considered without first ascertaining what the respondent’s process is, as it is obvious that the two processes must be compared in order to determine whether they are substantially the same in principle and mode of operation, or substantially different, which is the criterion by which to determine every such issue as the one under consideration. Factories have been erected by the respondent for manu *413 facturing candles, and he is largely engaged in that business, but he denies that he uses the alleged improvement of the complainant, or any method of decomposing neutral fats embracing the means and mode of operation described in the specification of the complainant’s patent. He admits that in his process of manufacture he uses water at high temperature, and steam, and that he also uses such pressure as arises from the expansive force of hot water or steam in a close vessel.; that he is engaged in manufacturing candles under and in pursuance of letters-patent granted by the United States' of the twenty-fifth of January, 1859, to Wright and Fouché, as subsequently amended, but he denies that he employs either the method, process, or apparatus described in the complainant’s specification. Appropriate means are at hand to enable the court to make the comparison, as the patent under which the respondent works was given in evidence at the hearing. * On the face of the patent it purports to be a new and useful improvement in process for decomposing fats, and it appears that the inventors obtained a patent for the improvement in France two years before the complainant left England to return to the United States, and more than three years before the complainant obtained his new patent in this country, in which he left out all of the extreme and unexampled conditions of the old patent, and in which he stated under oath that he verily believed he was the original and first inventor of the improvement, and that it had never been known or used before his then application was filed. . Wright and Fouché describe their invention in their specification as a new apparatus destined to produce chemical decomposition by means of superheated steam and water, and that it is chiefly intended for the decomposition of fatty substances into fat-acids and glyceriu,and they particularly describe the means to be employed and the mode of operation when the patented method is applied to that purpose. Drawings are annexed to the specification, which *414 contain figures of the apparatus to be employed in applying the patented process in the decomposition of fatty substances to obtain fat-acids and glycerin. Two vessels constructed of irou or copper are required for the purpose — one is called the boiler in the specification, which it is said may be of any form, and the other is called the cylinder, aud is placed on a base and elevated higher than the boiler. Both áre required to be sufficient!}7 strong to resist a pressure of from ten to twenty atmospheres, and of a capacity varying according to the requirements of the manufacture, and they are connected by a tube extending from the bottom of the boiler to the bottom of the cylinder, and also by another tube, called in the specification the tube for ascension to conduct the superheated water from the boiler to the upper part of the cylinder, which terminates in the interior of the cylinder by a rose-jet, or holes may be made in the end of it, so as to distribute the water uniformly in the cylinder and to insure the intimate contact between the superheated water and the fatty substance subjected to the process. Fatty substances to be subjected to the process are placed in the cylinder, which, with other things, is furnished with a pressure gauge to indicate the pressure in the apparatus used with devices to indicate the height aud level of the substance and of the water in the cylinder. Everything being arranged as described for applying the process, the boiler is completely filled with water and the cylinder is filled with water to one-third of its height, and then it is filled to the level of the upper cock, shown in the drawings, with the fatty substances to be decomposed, the latter substance or substances being above the water in the cylinder, which is still not filled, there being a vacant space in the cylinder above the fatty substance. Ileat is then applied to the boiler, which is placed in a furnace where it may be exposed to fire. ' By the direction the heat is to be gradually applied until the pressure gauge indicates a pres sure of ten to twenty atmospheres, according to the nature of the fatty substance to be decomposed. Minute description is then given of what it is claimed *415 takes place in the apparatus. Superheated water it is said acquires an ascending motion, whence it results that the heated water in the boiler ascends through the described tube into the cylinder, and being forcibly drawn out through the holes in the described rose-jet, passes through the fatty substance to the vacant space above, where the temperature being reduced, it descends through the other described tube to the bottom of the boiler, where it is again heated and then recommences its ascending motion as in the first instance, and so on during the operation. Suggestion is made that the operation may be continued from five to eight hours, according to the nature of the fatty substance composing the charge and the degree of heat and pressure applied, and it is claimed that the result will be that the fatty substance will be decomposed and that the product will be fat-acids aud glycerin. In their specification they admit that it is a well-known scientific fact that fatty substances maybe decomposed by water under the influence of heat and pressure, which could not well be denied in view of the fact that water or its equivalent was used in all the prior processes of saponification, and of the great mass of other evidence to support that proposition which is embodied in this record. Consequently those inventors do not claim to be the discoverers of that scientific truth. All they claim is that their invention consists of an apparatus wherein water and the fatty substances are heated separately in two different boilers, the first boiler being heated in the furnace, called in the specification the source of heat, while the second boiler, called the cylinder, is heated from the first boiler. Unlike as the two processes are in so many material characteristics, it seems almost a work of supererogation to enter much into details, as the dissimilarity is apparent in the whole description of the respective inventions, except that both contemplate the employment of heat and water in effecting the decomposition of fatty substances ;• and even in that respect, they are widely different, as the patentees under whose patent the respondent works employ only *416 moderate heat as compared with the other process, never exceeding in practice what is represented by a pressure of one hundred and eighty pounds to the square inch; and they also employ steam as well as water in a vessel which is never filled with the fatty substance or with water or with both combined. None of the other characteristic conditions of the complainant’s invention are found in the specification of the patent under which the respondent works, full proof of which is shown in the enumeration of those conditions, which are as follows: 1. That the fatty substances to be treated must be first mixed with water equal in bulk to one-third or one-half of the fatty substance. 2. That for that purpose the fatty substance and the water in the proportions mentioned must be put into the described receiving vessel, where.it must be subjected to the action of the piston with the perforated disk until it causes the fat and the water to form an emulsion or intimate mechanical mixture. 3. That the mixture so formed must then be driven by a force-pump through the connecting tube into the heating vessel, whether a coil of iron tubing or other convenient vessel, and be subjected to a high degree of heat and pressure for ten minutes to effect the decomposition of the fatty substance. 4. That the heating vessel must be closed and of great strength, so that the requisite amount of pressure may be applied to prevent the conversion of the water into steam. 5. That the heating vessel must be filled with the mixture and kept entirely full of it throughout the operation. 6. That the only means suggested to fulfil the condition is the forcing pump, as the provision is that if necessary the speed of the forcing pump should be increased. 7. That the heating vessel must be kept full of the mixture, so that no steam or air shall accumulate in the heating vessel, and to preserve the intimate mechanical mixture of the fatty substance and the water, as the description does *417 not suggest any means to supply any deficiency of water in any other way, whether occasioned by evaporation or by its being converted into steam. 8. That the temperature required for the operation, if the fatty substance be such as palm oil, is 510° Fahr., or if such as beef tallow or the tallow of sheep, it must be carried to 610° Fahr., or the melting-point of lead. 9. That the heating vessel should be tested before taken into use by a pressure of ten thousand pounds, and should be of sufficient strength to be safe at a working pressure of two thousand pounds to the square inch. 10. That the apparatus must be furnished with gauges to indicate the required heat to he applied in the operation, and with a refrigerator near the exit end of the apparatus to cool down the product from its high temperature below 212° Fahr. before it is discharged into the receiving vessel. Compare these conditions with the specification of the patent under which the respondent works and it is clear that he does not use any such method, process, or operation as those described in the letters-patent of the complainant. Witnesses have been examined by each party as experts, to assist the court in making the comparison, but they differ so widely in their statements as to afford the court but little aid in the solution of the question. Attention is also drawn to the fact that several circuit judges have decided otherwise, to which the proper reply seetns to be that the proofs ¡before the court are much fuller than on any former occasion, and that the conclusion stated is the best one the court can form after having given the whole record an attentive examination. Expert witnesses on both sides have been examined also upon the issue of infringement, but they differ so widely in opinion that their testimony affords the court but little aid in deciding the question, which after all must depend chiefly upon the comparison of the descriptive portions of the two specifications. * *418 Two tilings are not the same under the patent law when one is in practice substantially better than the other in a case where the second improvement is not gained by the use of the same means or known mechanical equivalents. * Patent laws have for their leading purpose the encouragement of useful inventions. Practical utility is their object, and it would be strange if with such object in view the law should consider two things substantially the same which practically and in reference to their utility are substantially different. † Slight differences in degree cannot be regarded as of weight in determining the question of substantial similarity or substantial difference, but in all cases the question whether the difference in degree is sufficient or insufficient to prove the alleged infringement is a question of fact to be determined by the jury in an action at law, or by the court in a suit in equity. ‡ Differences, however, so great as are exhibited in this record relieve the case, in the judgment of the court, from all doubt, and warrant the conclusion that the process under which the respondent works is substantially different from that of the complainant. On the twenty-third of November, 1867, the patent of the complainant was extended for seveu years from the expii’ation of the fourteen years for which the original patent was granted. Subsequently, to wit, on the sixth of March, 1871, the complainant instituted a second suit against the respon dent founded upon the extended patent, which is number 840 on the calendar. Both cases were heard at the same time. Suffice it to say in respect to the latter that the pleadings, issues, and proofs in the two cases are substantially the same, and that the latter must be disposed of in the same way as the preceding case. Decrees were entered in these cases respectively in the *419 Circuit Court in favor of the complainant, each of which must be reversed. Decree in each case reversed with costs, and the cases respectively remanded with direction to dismiss the respective bills of complaint. Justices SWAYNE, STRONG, and BRADLEY dissented. Mr. Justice DAYIS took no part in the judgment. Footnotes [*] 1 Regnault’s Chemistry, § 1592. [*] Turner’s Chemistry, "by Johnston, 8th edition, p. 456. [*] Silliman’s Chemistry, 25th edition, p. 441. [†] 3 Miller’s Chemistry, 370, § 1141; 2 Ure’s Chemical Dictionary, 5th edition, 379. [*] 2 Watts’s Chemical Dictionary, 894; Attfield’s Chemistry, 394; Sillinian’s Chemistry, 25th edition, p. 44, g 763. [*] Agawam Co. v. Jordan, 7 Wallace, 597. [*] Seymour v. Osborn, 11 Wallace, 538. [†] Ib. 547; Curtis on Patents, § 242. [*] Househill Co. v. Neilson, 1 Webster’s Patent Cases, 683; Curtis on Patents, 4th edition, 279; Foote v. Silsby, 2 Blatchford, 200. [†] O’Reilly v. Morse, 15 Howard, 119; Curtis on Patents, 4th edition, § 163. [*] Green v. Wood, 7 Queen’s Bench, 178; Potter’s Dwarris, 199-200. [†] Railroad Co. v. Stimpson, 14 Peters, 458; Curtis on Patents, 4th edition, § 472. [*] O’Reilly v. Morse, 15 Howard, 119; Curtis on Patents, 189. [†] Curtis on Patents, 4th edition, § 449. [*] Cuitis on Patents, 4th edition, §§ 106 and 449. [*] See supra, p. 321. — Rep. [*] Supra, pp. 336-341. — Rep. [*] Supra, p. 344. — Rep. [*] Supra, p. 345. — Rep. [†] Supra, pp. 344, 345, 350. — Rep. [‡] Supra, pp. 345-348. — Rep. [*] Supra, pp. 307-8. — Rep. [†] Supra, pp. 335-6. — Rep. [*] See supra, pp. 353-355. — Rep. [*] See it, supra, pp. 298-304. — Rep. [*] Hill v. Thompson, 1 Webster’s Patent Cases, 232; Turner v. Winter, Ib. 77. [*] Curtis on Patents, 4th edition, § 330. [†] Ib. § 331. [‡] Cahoon v. Ring, 1 Clifford, 621.