A Manual Of Photography

CHAPTER VII. THE COLLODION PROCESS. With the advance of this beautiful art, there appears to be a progressively increasing desire to produce more artistic results; and numerous improvements have recently been introduced. Collodion, as the basis of the photographic agents, beyond all other preparations, offers, in its exceeding sensibility, beauty of details in the finished pictures, and ease of operating, so very many decided advantages, that a separate chapter has been devoted to its consideration. Collodion is a peculiar preparation, formed by dissolving gun- cotton in ether. It is a very mucilaginous solution of a volatile character, and the ether evaporating leaves a film of the utmost transparency behind. It is not al1 kinds of gun-cotton which dissolve equally well in ether. According to my experience the most easily soluble is prepared by soaking good cotton in a saturated solution of nitrate of potash for some time ; it is then, in a moist state, plunged into sulphuric acid with which but a small quantity of nitric acid has been mixed: after remaining in the acid for about a minute, it is well washed witli water until no trace of an acid taste is discovered, and then dried at a temperature but very slightly elevated above that of the apartment. Mr. Archer, to whom, in conjunction with Mr. Fry, we are mainly indebted for the introduction of this preparation as a photographic agent, gives the following as his processes for preparing gun-cotton. "There are two receipts for making gun-cotton, from either of which a good dissolving cotton may be obtained. Several others have been described, but I should only be confusing the subject to attempt to give the whole ; and it would be foreign to the limited purpose of this work to do so. The results, however vary so much witli the strength and proportion of the acids used, as to render it extremely difficult to name any one in particular whicli would entirely succeed under all circumstances all cases it is more easy to prepare a cotton which will explode readily, and yet not Lc at all soluble, than one which will entirely dissolve in rectified sulphuric ether.