(after stating the facts). The patent, after the brief statement of invention in paragraph 2, sets forth, in paragraph 3, what has been aptly called a “general description” of the process to. be followed in order to obtain the product sought to be patented, .and, in paragraph 4, gives a specific description “as an example” of the process of carrying out the manufacture of the product when certain starting ingredients named therein are used. This paragraph has been aptly called the “special process.”
To the validity of the patent, it is objected that the specification fails to disclose a process which will result in the product, because of errors and omissions in paragraph 4. If the directions of that para*913graph are literally followed, no dye stuff of a blade color, and capable of dyeing shades of dark blue, will be produced. The error consists in calling for the “addition of seven kilograms of nitrate of sodium,” instead of the same quantity of “nitrite of sodium.” The evidence in the case sustains the finding- of the circuit court that this error is immaterial, for the reason that no one skilled in the art would be misled by the mistake, “since it was well known at the date of the paient that it was necessary to use nitrite of sodium to carry out the diazotization in the manufacture of coal-tar colors, and that the use of the word 'nitrate’ for 'nitrite’ was common in the earlier United States azo pa tents.”
The omission from paragraph 4 is of any express direction for a second diazotization, whereby the amido-azo compound is converted into a diazoazo compound. On this point, again, we concur with the judge who heard the cause in the circuit court, in the finding that this error of omission is immaterial, since any one skilled in the art would have understood that there was to have been a second diazoti-zation, because it is so stated in the general description or formula of paragraph 3, and also because paragraph 4 itself indicates that the product of the first steps of the “special process” is to be a diazo-azo compound, which would be sufficient “to inform any practical coal-tar manufacturer that a second diazotization was necessary.”
It appears that the specification as originally filed called for “nitrite” of sodium, and not “nitrate,” and gave specific directions in paragraph 4 to diazotize a second time. Defendant contends that the variance in these respects between the specification as filed and as finally amended cannot be claimed to be inadvertence, but, ou the contrary, wms a distinct and intentional change, and that the court should find that the patentee, for the purpose of deceiving the public, caused his specification to contain less than the whole truth relative to his invention or discovery, and should therefore hold the patent absolutely and ab initio void. Simpson v. Holliday, 33 Wkly. Rep. 577. The applicants for this patent were in Europe and their solicit- or here evidently knew little, if anything, about the chemistry of azo products; and there is nothing in the record to suggest that the changes -which the solicitor made were due to anything except his own ignorance,, or that he had any intent to mislead or to conceal. It is not doubted that an applicant is bound by the acts of his solicitor, but this contention seems to go beyond this wholesome rule when it seeks to void a patent, upon the theory of a fraudulent concealment or fraudulent misrepresentation, because, through the solicitor’s ignorance, the specifications, when describing the process of manufacture, contain some immaterial error or omission, which could not mislead a person skilled in the art.
It is next objected that the patent is void because, as is alleged, a person skilled in the art, making the corrections of error and omission above set forth, and following the special process of paragraph 4, would, nevertheless, not succeed in jjrodacing the “naphthol-black” which, that paragraph asserts to he the product of such process. The issue raised upon this branch of the case is tersely .stated in appellant’s brief:
*914“The bodies referred to in the example [of the special process] are, in the first place, naphthylamine disulphonate of sodium; in the second place, the clilor-hy-drate of alpha-naphthylamine; and, in the third place, beta-naphthol alpha-disul-phonate of sodium (salt K). The last two terms relate only each to a single body. The words 'naphthylamine disulphonate of sodium’ relate to a number of bodies. Complainant’s expert says five were known at the date of the patent, — acid 11, acid G, and three other acids. ⅜ s * Defendant’s expert, a chemist .of the highest science, * ⅞ * tried in vain to produce the coloring matter of the patent using these acids, and adding thereto the knowledge of the art as known to him. [This, of course, with the corrections above set forth.] In carrying out. these experiments, he took the instruction of the art for the making of the acids he used, * ⅞ * and [with the acids thus made] entirely failed to produce the results aimed at in the patent.”
Complainant’s experts, on the other hand, insist that the difficulty with these experiments was that the acids used were not pure; and although they admit that the literature of the art, if followed in the manufacture of these acids, would have resulted in acids more or less loaded with impurities, they insist that one skilled in the coal-tar color art, when instructed, as he was by this patent, to take acid R, or acid G-, or what not, would have understood that, before using such acid as starting material for producing an azo coloring matter, he should test it for impurities, and, when found, remove them. Upon this branch of the case, the evidence is voluminous and highly technical. The judge at circuit reviewred it at great length. It is, of course, purely a question of fact, the discussion of which need not he entered into in this opinion. The pertinent rule of law is correctly stated in appellant’s brief:
“Patents [such as this] should be so plain under the statute as tbat an ordinary manufacturer of aniline colors, having such ordinary knowledge as would exist in this country at the date of the patent, should be enabled by the instructions of that patent to carry out successfully Us processes.”
The weight of evidence seems to support the findings of the trial judge that:
“It was the common practice in coal-1 ar factories, at the date of the patent in suit, to test 1ho raw materials to be used in the manufacture of colors, in order to ascertain their character and degree of purity.”
It appears that, when naphthylamine disulphonate of sodium is used technically pure, — i. e. not chemically pure; but only in that degree .of purity which the practice of the art requires, — the reactions of the patent may he affected. It would therefore appear that the circuit court correctly found that:
“The specifications of the patent in suit are sufficient to enable a person skilled in the art to obtain the product of the patent, using the ordinary knowledge of the class of persons to whom the patent is addressed.”
A much more serious objection to tine validity of the patent arises by reason of what complainant’s counsel calls the “effort of the inventors to protect themselves against such as might try to steal their broad discovery.” Referring again to the patent, the following-analysis of it is found in the testimony of complainant’s experts:
“The patent in suit was the first printed publication which described a process by which a black dye could be produced from coal tar. The patentees declared their broad invention, and described it in [paragraph 3]. They said: ‘If you take any sulpho acid of any radical, and treat as we direct you, you will get a color producing black.’ By this declaration they opened their discovery broadly to the *915public, concealing nothing. Then they proceeded [paragraph 4] to take one radical naphthyl, and describe specifically the production of the black color from it. Haying done so, they proceeded [paragraph 5] to describe some characteristic relations, other than their use in the art, by which they might, be known and identified [the "tests” of the fifth paragraph]. Of course, with the change of the radical there is a change in the chemical composition of the product; but. in the art the patent, in effect, declares that one is the equivalent of the other, and may be used as a substitute for the other, and that they are therefore technically the same.”
In other words, the patentees, according to this construction of the patent, say:
“We described here a special process, whereby, with one of the general group of chemical compounds which are known as ‘sulpho acids’ as starting; material, we produce a black dye. This, however, we give as an example, for we hereby announce to the world that we have discovered that it you take any sulpho acid of any radical, and treat it according to our process, you will get a coloring producing black; wherefore we shall insist (hat whatever particular sulpho acid any one may hereafter use to obtain this result is an equivalent of the one we use in the special process.”
ÍTow, the evidence shows, and it is not disputed, that the phrase “any sulpho acid of any radical” — which is, the translation of the general formula, “R (8 O» IJL)x — N—JST—Oio He j\ H2 (a)” — ⅛ a very broad one, covering over 100, possibly as many as 500, different sulpho acids. It is proved and conceded that, very many, in fact nearly all, of these, will not, when treated according to the pat-entee's process, produce the patentee’s color. In other words, when the inventors said, "if you take any sulpho acid of any radical, and treat it as we direct you, you will get a color producing black,” they made a. false statement. Complainant's experts insist that this would mislead no one. They say:
“The preparation of these various bodies [other than what the special process specifically names I. and the tests of their capability of forming naphtliol black compounds, would require several yours; and therefore any one would know that the patentee had never done this, and did nol mean to be so understood. * * * The patentee ::: ⅞ ⅜ gives a general description of the whole possible scope of his discovery, and thereby intimates that, though he cannot possibly himself have tried all the hundreds of bodies which fall under the general formula, still it is probable that many of them will fit into his process, and produce his product. But he confines his positive assertion to what he has himself actually tried, as set forth in his example: that is, the naphthylamine disnlpho acids, or, rather, Ills' sodium salts thereof.”
In other words, having himself experimented only with three or four bodies out of a group of hundreds, he proposes to set himself in the pathway of future experimenters with a,ny or all of the other bodies, and, as the result of each new experiment is disclosed, will lire away at it, calculating to “hit it if it is a deer, and miss if it is a cow.” That this is precisely what is contended for is manifest from the statement, prominently set forth in ap-pellee’s brief:
“The inventors were entitled to protect themselves against such as might try to steal their broad discovery, by tlu> general statement that many of (he bodies included in the general formula might, when subjected to their process, produce naphthol-blaek; and that the products so produced from those that did work wore the equivalents of the product resulting from the specific materials set forth in the example. Without this or something of the kind, the real invention could have been appropria led with impunity, and this pioneer patent for a most valuable discovery would have been almost valueless to the inventors.”
*916This assertion- at once. suggests two criticisms: (1) The patent contains no general statement that “many of the bodies included iii. the general formula might,” etc. The general statement is that “all such bodies will,” etc. (2) The inventors did not make any such “broad discovery.” They made the specific discovery that some di-shlpho acids, treated according to their process, would produce their product. The broad discovery that all sulpho acids may be thus transformed they certainly did not discover, for it is apparently undiscoverable, since most of them cannot be thus transformed by the process of the patent. Some future experimenter will have to make some new discovery, and invent some new process, before these other sulpho acids can be transformed into naphthol-black. We are referred to no authority, and know of no principle, which will sustain the complainant’s contention that he can thus, in the language of the circuit court, “speculate on the equivalents of his claimed invention, and thereby oblige the public to resort to experiments in order to determine the scope of the claims of his patent.”
The appellant insisted that the multifariousness of the general formula and description invalidated the whole patent; but the circuit court reached the conclusion that it could be held- valid, by limiting it so as to embrace only the product of the special process, definitely stated, and applied to naphthylamine disulphonate of sodium, "as specifically claimed. The argument in support of this construction may be best stated in excerpts from the opinion below:
“The general statement may be fairly considered as a disclosure to the public of the general character and scope of the discovery, inserted merely as a help to a better comprehension of the special process of the patent. As is stated by complainant’s expert, a chemist -would more readily understand the process and reactions from such a graphical formula than from a genera] description. A comparison of said-statement-with the special process, and an examination of the claim, show that the general formula only describes the class of bodies to which naphthyl belongs, and covers only the first step in the reaction. It does not profess to give a resulting color product. ⅞ ■* * When the patentees undertake to describe the complete process, and to claim the resulting product, they confine the application of the process to a single body, and the tests and claim to a single product. It does not appear that a person skilled in the art, upon reading the patent, would have been misled into supposing that all the compounds covered by the general formula would produce the patented color, or, upon an examination of the whole patent, would have understood that it purported to describe all the bodies included under the general formula. The patentees say that ‘the present invention relates to a new method for manufacturing blue to a violet coloring matter belonging to-the azo group.’ They then say: ‘We take one of the compounds corresponding to the general formula,’ etc., and treat and convert it. Then follows the special process for obtaining one of the various ‘coloring matters belonging to the azo group,’ namely, naphthol-black, with appropriate tests, and a claim limited to the single product of the special process upon the special body ‘naphthyl.’ ’’ ■ . . .
Referring to tbe rule of interpretation that a patent must be construed in conformity with the.self-imposed limitations contained in the claims, the court proceeds:
“In the case at bar the case is- confined by ‘the herein-described dye stuff, * * as- set forth.’ The only dye stuff described is the filtered coloring matter delivered to the trade as a black paste or in solid form, of the special process.1 *917The general statement contains no reference to a product. Manifestly, the claim could not he construed to cover any body other than naphthyl of the special process, either upon the question of infringement or validity.”
And the conclusion arrived at is that the patent may fairly be construed as a patent for the definite product of the special process. Such construction would, of course, naturally reduce the range of equivalents within extremely narrow limits. The conclusion we have reached as to the question of infringement, however, renders it unnecessary to decide this question of construction upon this appeal.
It must be borne in mind that, in the practical determination of questions of alleged infringement, the problem is very dliferent when we are dealing with a chemical compound than it is when we are dealing with a machine. Such observa! ion as the eye can give to the machine at rest and in action, illuminated by a comparison of the co-ordination of its parts with that of like parts in other machines, will be ordinarily sufficient to determine its classification. Far different is it with a chemical compound. No mere observation by the eye, supplemented even by the taste and touch, can go very far towards a solution of the problem. The same mysterious forces through whose action and reaction the compound was produced must be availed of to disintegrate and disrupt, before there can be any assurance of what it is we have before us. Hence it is that so-called “tests” are devised by those skilled in the art and science of chemistry, which, in their opinion, as experts, will reveal the secrets of the composition sufficiently to make the answer to the question positive enough to support the judgment of a court.
An inventor takes certain starting' materials, and subjects them to a, process he has devised. The result is a product. If he sufficiently describes the starting materials and the process in Ms patent, he may claim the product, being new; but, if he simply defines what he claims as the “product of his process,” he might find it an extremely difficult matter to prove infringement. “Every patent for a product or composition of matter must identify it so that it can be recognized, aside from the description of the process for making it, or else nothing can be held to infringe the patent which it not made by that process.” Cochrane v. Badische Anilin & Soda Fabrik, 111 U. S. 293, 4 Sup. Ct. 455. Now, there are many tests that may be applied to two bodies which are being compared in order to determine whether they are or are not identical. The number of these tests may be multiplied indefinitely, for the skill, the experience, the scientific ingenuity of the chemist, will ever devise new ones in the future, as they have the old ones in the past. Some of these tests will be of great significance; some, almost crucial; others will be of but minor importance. Their relative value, no doubt, may change as science goes sweeping on from point to point; but it must be sound law, as it is reasonable common sense, to hold that the tests of prime importance in a suit for infringement are those which the patent itself prescribes. The inventor certainly may be assumed to know what it is that he has invented. If any one is able to describe the product of his inventive *918skill, it is himself. He surely knows the earmarks of the thing he seeks to patent, and when, out of the multitudinous qualities which his product may exhibit under varying conditions and in different relations, he has selected and set forth in his j)atent a chosen few, surely these should be accepted as the distinguishing earmarks,— the characteristic stigmata of the product his patent is to coArer. It may be that, after it is found that the body under investigation responds to all the tests of a patent, science may yet be able to demonstrate by other tests that, nevertheless, it is not the new' product therein patented;, that the patentee had selected identifying tests broader than he was entitled to, and which would cover products not within the range of his discovery. But, when the body under investigation fails to respond to the specific tests the pat-entee has himself selected, he certainly cannot fairly insist that it is identical with his product.
In framing the patent in suit, care was taken to avoid the difficulty pointed out in Cochrane v. Badische Anilin & Soda Fabrik, supra. Certain identifying tests were set' forth, so that the inventors might be able to contend that a chemical compound which responded to them all was, prima facie at least, an infringement of their patent. The tests of the patent are:
First. The dye stuff is a black paste or in solid form; and, though the patent does not say so, this test would be fairly responded to if the black solid had been mechanically transformed into a black powder.
Second. It produces on the fiber, in an acidulated bath, dark-blue shades.
Third. It is very soluble in water.
Fourth. It is insoluble in spirit.
Fifth. It dissolves in strong sulphuric acid with green color.
Sixth. Keducing agents destroy the color-forming alpha-naphtliylamine besides other products.
The dye stuff as to which it is to be determined whether or not it infringes is the dye stuff sold by defendant, of which a can was, by stipulation, put in evidence, as “Complainant’s Exhibit, Defendant’s Color.’’ There is no evidence at all in the case by what process the dye stuff was made. Complainant therefore undertook to prove infringement by the application of “tests.” His expert testified that he had applied 34 tests, and that of those tests 5 are named in the patent. We have carefully examined his enumeration of the tests he applied, and fail to find therein more than 4 of the tests of the patent, viz. the third, fourth, fifth, and second. In applying the fourth test, he used both methylic alcohol, in which it was soluble, and ethylic alcohol, in which it was not; but he evidently does not mean lo imply that these are to be taken as two tests under the patent, for, if the various double and triple tests of his enumeration are to be thus split up, the list will number more than 34. The evidence supports the conclusion of the circuit court that the words “insoluble in spirit” refer to ethylic alcohol, not to methylic alcohol. To the four tests of the patent which complainant’s experts applied, the defendant’s dye stuff responded.
The testimony as to the first test of the patent is not very satisfactory, but, in view of the sense in which the word “black” appears to be used in this art, we are not prepared to say that de-*919fondant’s color failed to respond fairly to this test. Tlte sixth test above quoted from the patent brings up a question of construction. It reads “reducing agents destroy the color-forming alplia-naphthylamine besides other products.” Even without any evidence, it is apparent that the sentence is awkwardly expressed. It seems to imply that the black paste or solid consists of alpha-naphthylamine, which forms the color, and of other x«'oducts, and that reducing- agents destroy them all. The proof shows conclusively (all the experts agreeing) that there is no alpha-naphthyl-amine in the black paste or solid. The alpha-naphthylamine perished long before the ultimate black paste of the patent-appeared. Complainant's expert suggests that the sentence means that, “by reducing agents, alpha-naphthylamine, which was used to form the color of the patent in suit, and therefore in the patent, is named the color-forming alpha-naphthylamine, is destroyed.” But this is not materially helpful, for he says that reducing agents would not change alpha-naphthyhunine at all, and he most certainly concedes that, in the ultimate product of the patent, alpha-naphthyl-amine does not exist as such. The sum of his testimony is that the reducing agents are to he applied to the color. In the light of the testimony, the sentence, as it stands, is, if not meaningless, at least ambiguous. It is apparent that the awkwardness of the sentence arises from the use of the hyphen between “color” and “forming.” If that were eliminated, all concede that the plain meaning of the sentence would he that reducing agents would destroy the color, and alpha-naphthylamine would be formed. And the same result would follow if the hyphen were made a little longer, so as to become a printer’s dash. It is not necessary, however, to theorize upon this point, or to guess at the meaning of 1he sentence. It is demonstrable by evidence well recognized as compete:! it in patent causes that the presence of the hyphen is due to a printer’s error.
The hie wrapper shows that as to tests the original specification read as follows:
“These new dye stuffs produce on wool and silk, in an acidulated bath, violet to dark-blue shades. They are very soluble in water, insoluble in spirits, and dissolve in strong sulphuric acid with green color. They ¡ire destroyed by reducing agents, forming aiplia-naphtylendiainine besides other products.”
Subsequently this part of the specification was amended so as to read as follows:
“Naphthol-blaek produces on the fiber, in an acidulated bath, dark-blue shades, It is very soluble in water, insoluble in spirit, and dissolves in strong sulphuric acid with green color. Tteducing agents destroy the color, forming alpha-naph-thylamine, besides other products.”
And in this form it wras allowed by the patent office. That the hyphen was inserted in the printed copies issued by the office through a printer’s blunder is manifest. It is apparent, then, that the inventors prescribed, as one of the tests which would disclose the identity of any body with their product, the action of reducing agents thereon. This action must he such as to destroy the color, and form certain products. The characteristic product of *920those thus formed, the orce which they selected as determinative under this test, they originally declared to be “alpha-naphtylendia-mine.” Subsequently, and before patent issued, they changed that declaration to “alpha-naphthylamine.” There is no evidence that one skilled in the art would know, when he saw “alpha-naphthyl-amine” named as the identifying product, that it was a misnomer for “alpha-naphtylendiamine.” We know no reason why they should not be held to the selection they thus declared to the public as one of the characteristic tests of their product. If this were a blunder of an ignorant solicitor, they had ample opportunity to correct it by reissue; but, having allowed it to stand in their patent, they must be'held to their declaration that reducing agents will produce this result. It has been suggested that since the evidence shows that alpha-napthylamine would not be formed out of the product of the patent by reducing agents, and that persons skilled in the art would know that fact, the entire test may be rejected as nonsensical surplusage. jBut there must be some limit to a court’s functions in rewriting patents. Assuming that all the imperfections in this patent were due to an ignorant solicitor, remote from his clients, — and it may be noted that there is no evidence of this, — it does not follow .that all should be disregarded. We held, as to the error and omission of paragraph 4, that the omission was really supplied elsewhere in-the patent; that the error was harmless, since the skilled workman would himself substitute “nitrite” for “nitrate”; and that, although the error must stand in the patent where the patentee’s careless solicitor had placed it, we would not infer from its presence that it was due to a fraudulent design to mislead, formed and carried out by the pat-entees. But here there has been an identifying test put into the patent by the solicitor; the patentee accepts such patent, and applies for no reissue, alleging no mistake; and the court is asked to strike out the test altogether, as ridiculous surplusage. In the absence of any authority for such action, we are unwilling to establish the precedent. By what their solicitors do, patentees should abide. If they are dissatisfied with the letters patent their solicitors obtain, they may, in proper cases, apply for a reissue; but, when they accept their original patents without objection, they must be assumed to have assented to such changes as were made by their solicitors in specification or claim while their application was on its way through the patent office.
When the defendant’s coloring matter is treated with reducing agents, it is destroyed, but no alpha-naphthylamine is formed.. We have, then, a case where the inventor has prescribed six tests in his patent, and an alleged infringing body responds to five of them, but fails to respond to the sixth. Manifestly, it is not absolutely' identical with the product of the patent, as the inventor has defined that product by distinguishing characteristics. It may be that the variance results from some immaterial change in the process, from the use of starting material, which is within the fair range of equivalents; but, having failed to prove identity by the p'rescribed tests, the burden is on the holder of the patent to show *921that tlie variances in process are immaterial, or the starting materials equivalents of those of the patents. There being no such proof here, tlie complainant must stand or fall by the results of the tests of the patent; and, since the defendant’s color does not respond to these, it cannot be held to be an infringement. The conclusion thus reached renders it unnecessary to discuss the other points raised in the case. The decree of the circuit court is reversed, with costs, and cause remanded, with instructions to dismiss the bill. >