A Manual Of Photography

46 HISTORY OF PHOTOGRAPHY. discovering the properties of these different metals, one of which aids in promptitude, the other in the vigour of the im- pression, &C.1 " From the concurrence of these substances arises a power which neutralises all the unknown,effects which so often oppose the formation of the image.2 I think, besides, that Science and Art should not be interrupted by the consideration of a more or less long manipulation; we should be contented to obtain beautiful results at this price, especially when tire means of execution are easy. The galvanic preparation of the plate does not present any difficulty. The operation is divided into two principal parts: the first, which is the longest, may be made a long time previously, and may be regarded as the completion of the manufacture of the plate.* This operation, being once made, serves indefinitely; and, without recommencing it, a great num- ber of impressions may be made on the same plate. The new substances employed are :—Aqueous solution ^ of bichloride of mercury : Solution of cyanide of mercury ; White oil of petro- leum, acidulated with nitric acid: Solution of chlorine of gold and platinum. These are prepared as follows:— “ Aqueous Solution of Bichloride of Mercury.—8 grains of bichloride of mercury in 10,000 grains of distilled water. “Solution of Cyanide of Mercury.—A flask of distilled water is saturated with cyanide of mercury, and a certain quantity is decanted, which is diluted with an equal quantity of dis- tilled water. “ Acidulated White Oil of Petroleum.3—This oil is acidulated by mixing with it one-tenth of pure nitric acid, leaving it for at least 48 hours, occasionally agitating the flask. The oil which is acidulated, and which then powerfully reddens litmus paper, I I will only observe that the employment of all the metals which I indicate further on is indispensable; but the mode of applying them may be varied. 2 For, by multiplying these elements as in a pile, this power is aug- mented'and we are thus enabled to make the most indolent radiations act in the same time ; sueli as those of green and red. 3 The most suitable oil of petroleum is of a greenish yellow tint, and takes, at different angles, azure reflections. I have given the preference to tins oil over the fixed oils, because it always remains limpid, although strongly acidulated. My object in employing an acidulated oil is to reduce the metals to powder, and to retain this powder on the surface of the plate, at the same time giving greater thickness to the layer by its unctuous properties ; for the naphtha which, results from the distillation of this oil does not produce the same effect, because, being too fluid, it carries away the powder of the metals. It is for the same reason that I have lately recommended the employment of essence of lavender ratlier tlian that of essence of turpentine.