A Manual Of Photography

268 PRACTICE OE PHOTOGRAPHY. To develope the image pour the above over the plate, taking care not to carry the development too far. The proto-nitrate may he obtained by double decom- position, as recommended by Dr. Diamond: GOO grains of proto- sulphate of iron are dissolved in one ounce of water, and the same quantity of nitrate of baryta in six ounces of water ; these being mixed together, proto-nitrate of iron and sulphate of baryta are formed by double decomposition ; also, by dissolving sulphuret of iron in dilute nitric acid, as recommended by Mr. Ellis, who proceeds as follows: — To one ounce of nitric acid and seven of water, add a small quantity of sulphuret of iron broken into fragments. Stand the vessel aside, that the sulphuretted hydrogen may escape, and the acid become saturated with iron. Pour off the liquid, and filter. Then boil in a florence flask, to get rid of the sulphur, and again filter, when a dark green liquid will be obtained, which is the proto-nitrate of iron. This should be kept in well-stopped bottles, and protected from the air as much as possible, to prevent its changing into a pernitrate, in which state is is quite useless as a photographic agent. To develope the picture mix one part of the above proto- nitrate with three of water, and apply it to the plate in the ordinary way, when a most beautiful clear image can be obtained. The negative image being developed, a mixture of pyro-gallic and hypo-sulphite of soda, which has undergone partial decom- position, is poured over the plate, and then it is gently warmed. Upon this the darkened parts are rendered brilliantly white by the formation of metallic silver. This picture being backed up with black velvet assumes the air of a fine daguerreotype, without any of the disadvantages arising from the reflection of light from the polished silver surface. For this beautiful result photography is indebted to Dr. Diamond, who is still pursuing the subject with much zeal. We have also seen a similar effect produced by Mr. Fry and Mr. Berger, by the use of the proto- sulphate of iron solution and pyrogallic acid. The image is first developed by the iron and the solution poured off; immediately another of pyrogallic acid is poured on, and the effect is produced. The pictures are fixed with the hyposulphite in the usual method. A peculiar whitening process was introduced by Mr. Archer, which is as follows :— The picture being thoroughly washed in plenty of water, after fixing with hypo-sulphite of soda, is treated in the following manner.