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248 THE PHOTOGRAPHIC NEWS. [May 21, 1869. volumes, full of different specimens, show to what extent and with what success it has been practised. Mr. Swan commenced by coating his plate with gelatine, like Fargier, but poured the collodion upon it and removed it previous to exposure : this he called a tissue ; ho subse quently made this tissue more easily manipulated by backing it with paper, and this being successful, he ultimately found that he could dispense with the collodion coating. The evi dence of a most respectable and influential inhabitant of Newcastle, who followed with much interest Mr. Swan’s ex periments, has been made on oath to show that these modifica tions were made by Mr. Swan himself before their publication by others, and were therefore legitimately inserted in the com plete specification, the law allowing six months’ delay for the express,purpose of making such improvements and modifi cations. The tissue thus formed may be either made sensitive by the introduction of the bichromate at once, or by subsequent floating. When dry, it is exposed under a negative, and the hardened insoluble image or potential image is then on the surface, and would become undermined and wasted away if the tissue were immersed in water, as in the process of Poitevin and Bouncy. Mr. Swan therefore mounts the tissue upon a support pre vious to development; this support may be either tempo rary or permanent. If permanent—that is, if the picture be intended to remain upon the support finally—albumen co agulated by alcohol or heat is the cement employed, but in this case the images are reversed if ordinary negatives be employed. Mi. Swan therefore proposed to mount the pic ture previous to development on a “temporary support,” using india-rubber as the cementing substance, heavy pres sure being required to bring the surface of the coated gelatine and the paper coated with the caoutchouc into per fect contact. He then mounted the developed print upon another paper by means of gelatine or other similar cement, and re moved the temporary support by softening the caoutchouc with benzine, and then tearing the two papers asunder. The gelatine was afterwards rendered insoluble by the immersion of the print in alum. In the Yeak-Book of the Photo- GRAPIIIO News of 1868, Swan described a peculiar manipu lation, by which the use of the press and tl e subsequent immersion in alum were dispensed with. He took a weak solution of gelatine, and added a small quantity of chrome alum to it. He then immersed both the developed print and the paper upon which it was to be mounted in this solution, and brought the two surfaces together under it, thus expelling all air. The adhesion was perfect with cer tain precautions. Edwards substituted the gelatine compound of Swan, just referred to, spread upon paper, for the albumen-paper rendered insoluble by spirit, a modification of very doubtful value ; but the substitution of Mr. Swan’s manipulations, hitherto only used in one part of the pro cess, for those which Mr. Swan had alone used in another part, is due to Mr. Edwards, and their advantages were first recognized and applied by him. They were suggested, long previously to Mr. Edwards’ Patent, to Mr. Swan, but he failed to see their importance. In the preceding observations I have omitted to mention in its proper place that M. Despaquis, the holder of M. Poitevin's patent for carbon printing, has, for some time past, made very beautiful carbon prints upon talc, by coating that substance with the sensitive compound, and printing through it, washing away the soluble gelatine from the back. In the British Journal of Photography, April 17th, 1868, Mr. Carey Lea shows a very similar plan, but substitutes glass for talc, to which he confines himself, finding that paper rendered transparent will not do, but predicts that in the future the difficulty of using transparent paper may be overcome. The only novel features in Mr. C. Lea’s contri bution are, the use of reflected sunlight for printing through the glass, and a method of coating the plate before the ex posure with gelatine, previously spread upon paper, which, inasmuch as it contains sugar, and sticks readily to the moistened fingers, and only too often to the negative, is a very obvious proceeding. I have thought it necessary to bring before you these matters (although they are well known to many of you, and have been already recorded very fully, and in a most lucid manner, by Mr. Simpson, in his work on pigment printing), because they have lately been the subject of much comment and much distorted statement in the pages of an obscure publication. I venture to think, Sir, that the history of the invention of carbon printing is a worthy subject of discussion for this Society, and I recapitulate these known facts as a challenge to those who dispute them, in the hope of raising that discussion. II.— PRINCIPLES INVOLVED IN THE New PROCESS. I will now proceed to describe the process which is the chief subject-matter to which I have to call your attention. I venture to think that its main features are new, and that they are founded upon several observations which have escaped previous experimenters. 1. The first observation is one which I arrived at by a process of exhaustion. Being desirous of attaching the exposed film to a plate of metal for the purpose of develop ment, I tried every form of cement, until at last I found that no cement at all was necessary, but that, if the film was well washed in water, the sugar being removed, the insolu ble, inadhesive film would readily adhere to any plane surface impermeable to water, if air were excluded. The novelty of this fact has been called in question by Mr. Carey Lea, on the ground of his having previously stuck the soluble, adhesive tissue upon glass previous to development. I appeal to you whether there is any analogy between the two cases, with the single exception that water is the common medium employed. The immediate object is different; the substance employed is different; and the ultimate end is different, his sole object being to obtain transparencies on glass, my chief object to obtain perfect photographs on paper. 2. The second important observation is, that, if we cover the surface of a plate of glass or metal with a minute layer of some solid fatty or resinous body, the adhesion still takes place, and is sufficient during development while the film is wet, but prevents the adhesion after the film is dry. Hence a plate of metal or glass so prepared may be used as the temporary support during development, provided that that body used for coating it is infusible at the tempera ture employed. 3. The third important observation is, that the dry film, when separated from the greased plate of glass or metal, has exactly the surface of the support. If this be polished, the surface of the film is polished ; if this be matt, the film has a matt surface; and if the surface of the plate bo grained or tooled, the removed film of gelatine presents corresponding granulations or tool-marks. Prints, may, therefore, be obtained at will with every kind of surface, from the highest polish to the grain of coarse sketching paper or its imitation. 4. The fourth important fact is, that the gelatine film, which, although insoluble, absorbs water readily, and softens under its action, and which is usually attached to paper by gelatine and alum, forming a cement which is likewise more or less absorbent, may be rendered entirely non absorbent, and may be so fixed to paper that no friction, even under water at a boiling temperature, will remove it. This is effected by using a solution of shellac in ammonia as the cement, and allowing sufficient of this to be absorbed into the gelatine film before it is attached to the paper. The result is no longer gelatine, but insoluble gelatine (leather), rendered waterproof by resinous cement, and attached firmly to paper by the same- cement.