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plaintiff's patent, it appeared that this patent was for obtaining a certain useful product by subjecting a mixture of sulphur and caoutchouc to heat. The mixture was first made mechanically, and then, by the operation of heat, the character of the caoutchouc was changed so that it ceased to be liable to stiffen from cold, it was not decomposed by heat, and it was improved in elasticity. The patent extended to the incorporation of sulphur, and of sulphur only, with the caoutchouc by means of heat. The defendant subsequently obtained a patent for the combination of hyposulphate of lead and artificial sulphuret of lead with caoutchouc; that combined mass, acted upon by heat, was alleged by the defendant to produce more beneficial results, but the results were of the same character as those which were produced by the plaintiff's patent. 'Assuming,' said Turner, V. C., the materials thus used by the defendant to be different, the process of the defendant would per se be no infringement of the plaintiffs' patent. The plaintiffs confined their patent to sulphur; the defendant had used hyposulphate of lead and artificial sulphuret of lead. But it was alleged by the plaintiffs that the materials were not in truth. different, or at least that the materials which produce the result are the same. It was said that sulphate and sulphuret of lead do not of themselves produce the change, but that the change is produced by the sulphur which they contain, and which forms one of their several constituent parts; and that those parts being decomposed by heat, the sulphur combined with the caoutchouc and left a residuum of lead, which had no operation in the change which was effected. If the qualities conferred upon the caoutchouc by the process were imparted by the sulphur, it would no doubt be an infringement of the plaintiff's patent.' The judge's opinion, after examining the evidence, was, that the

evidence preponderated very considerably in favour of the plaintiffs.

The case of Talbot v. Laroche (15 C. B. 310) deserves attentive study for the questions raised in it as to the substitution of one chemical equivalent for another. The plaintiff was the inventor of a photographic process, patented in 1841. The specification claimed, amongst other things, the employment of gallic acid or tincture of galls, in conjunction with a salt of silver, to render paper more sensitive to the action of light; and also the making visible photographic images upon paper by washing them with liquids (meaning only, as other parts of the specification showed, gallo-nitrate of silver), which act upon those parts which had been previously acted on by light. Subsequently to the date of this patent, the collodion process was discovered, and the defendant having practised it, the plaintiff brought this action, alleging that this process was an illegal copy of his process. It was argued by the defendant-firstly, that the plaintiff had claimed only the rendering of paper more sensitive to light; whereas collodion, the substance he employed, was a different thing, being a solution of gun-cotton in ether; secondly, that when the collodion was put into the camera, it contained no gallic acid, a material essential to the plaintiff's process: thirdly, that in developing the image, he employed pyrogallic acid, and not gallic acid. Several scientific persons gave evidence that collodion was not only a different material from paper, calling into play processes not needed when paper was employed, but that it possessed peculiar photographic properties, as was proved by the fact that no gallic acid was required to render it sensitive, as in the case of paper; also, that pyrogallic acid was much more rapid in its action than gallic acid, and that it was, in many respects, a different thing from gallic acid. The questions

submitted by the judge to the jury upon this part of the case were these: Is the use of collodion with nitrate of silver and iodide of potassium the same as the use of paper prepared with nitrate of silver, iodide of potassium, and gallic acid? Is pyrogallic acid the same as, or a chemical equivalent for, gallo-nitrate of silver? The jury returned a verdict implying that, in practising the collodion process, the defendant had not infringed the plaintiff's process.

The difficulty that sometimes exists in determining whether one chemical process is, in contemplation of law, distinct from, or an illegal copy of another, is exemplified in the history of the case of Heath v. Unwin.

Under a patent for improvements in the manufacture of iron and steel, the patentee claimed the use of carburet of manganese in any process whereby iron is converted into cast steel;' and his specification stated, that the invention consisted in adding from one to three per cent. of the carburet to iron or blistered steel whilst in the crucible. The carburet of manganese was separately prepared, by subjecting oxide of manganese and carbonaceous matter to a strong heat, and the resulting carburet was then added to the crucible containing the metal to be converted into cast-steel. Upon the trial of an action for an infringement, it appeared that the defendant did not use any single substance answering to the description of carburet of manganese; but he placed in the crucible containing the iron or blistered steel some oxide of manganese and carbonaceous matter. These two substances would form during the process of conversion, and before actual union with the melted iron, carburet of manganese in a state of fusion; but the quantity of the carburet so formed was less than one per cent. of the weight of iron in the crucible. It was held by the Court of Exchequer, that

since the defendant had not contemplated the use of carburet of manganese, and had not known prior to the investigation that took place in consequence of the action, that the result of his adding the oxide and carbon was to produce the carburet-since, moreover, the patentee had expressly stated his invention to be the addition of the substance called carburet of manganese to the crucible, there was no infringement on the part of the defendant, for there was no imitation of the patentee's process behind a colourable variation. The specification was construed as claiming the use of one particular combination of carbon and manganese, namely, the carburet of that metal; and a particular mode of using that combination, namely, by putting a certain quantity by weight, in an unmelted state, into the crucible.

Heath v. Unwin subsequently went before the Court of Exchequer Chamber. A majority of the judges of that Court held that, inasmuch as the plaintiff had not limited his claim to the particular mode of using the carburet described in his specification, the defendant's process was an infringement of the patented invention, since it effected the manufacture of cast-steel by the employment of either carburet of manganese or a chemical equivalent. A minority of the judges thought that the defendant had not infringed the patent; for, though he had used a chemical equivalent for the carburet of manganese-viz. its component parts-it was not known at the date of the patent that such component parts were equivalent to the carburet, in such special applications of it as were described in the specification, and for the purpose there mentioned. Moreover, they thought that the defendant's process was an improvement upon the plaintiff's, for the same quality of steel was made at less expense, one crucible and one heating effecting the desired result.

When this extraordinary case came before the House of Lords, the judges were called upon to attend the argument, and give their opinions. Eleven judges attended, seven of whom concurred with the Court of Exchequer Chamber, and four disagreed. Notwithstanding this large majority, the two law lords who heard the case (Lord Cranworth and Lord Brougham) gave judgment for the plaintiff in error, thereby deciding that Heath's patent had not been infringed. 'I think,' said Lord Cranworth, that the use of substances thus producing carburet of manganese in a state of fusion was no violation of the patent. The substance for the use of which (inter alia) the patent was granted was a solid metallic substance capable of being broken into fragments and weighed, so that certain definite quantities might be put into the crucible with the steel. There is no evidence whatever tending to prove that, at the date of the patent, it was known to persons acquainted with the subject of manufacturing steel, that coal-tar and oxide of manganese would be a chemical equivalent for the carburet of manganese claimed by Heath. Indeed it is obvious

that the discovery of such an equivalent was made after the use of the carburet as a distinct metallic substance had been some short time in operation. It was itself a most valuable discovery, and would have legitimately formed the subject of a new patent. The costly nature of the substance claimed in the patent might, and probably would, have prevented its use altogether; and if, at the date of the specification, it was known to Heath, that by the use of two common substances, well known in commerce, more than one hundred fold cheaper than carburet of manganese, the same results precisely would be obtained as by the use of that material, the specification would have been bad, as not truly disclosing the invention. On the short ground,