L. TECHNOLOGY. 501 



negative, and treated as in the Albert process, after which it 

 is to be attached to a plate of zinc, which is accomplished by 

 a special manipulation, and it is then ready to furnish impres- 

 sions. These are obtained by treating as on a lithographic 

 stone, namely, by sponging with water, removing the surplus, 

 and then pressing over the surface of the plate a sheet of blot- 

 ting-paper. The ink rollers are next passed over it, the ink 

 adhering according to the action of the light. The advantage 

 of using the zinc plates in printing instead of glass, as is found 

 in the original Albert process, lies in the greater durability 

 of the former, and the immunity from the danger of cracking. 

 A very great pressure is necessary in this class of printing to 

 bring out certain tints,, and the glass plate, however thick, is 

 apt to be fractured. It is stated that fifteen hundred uni- 

 formly good prints can be obtained from a single film ; and, 

 if a larger edition than this be required, it is a very easy mat- 

 ter to prepare a number of films at the same time, so as to 

 have a sufficient supply for any purpose. 13 C, February 3, 

 1870,37. 



IMPROVED PHOTOGRAPHIC PROCESSES. 



Iii a late number of Nature we find a concise summary of 

 the most important advances in photographic processes for 

 the last two or three years, in which it is stated that the great 

 point arrived at is in dispensing almost entirely with the sil- 

 ver salts, the action of light upon the bichromates of potash 

 and ammonia being substituted. This is considered a matter 

 of great importance, as replacing a very transitory and uncer- 

 tain method by one that is permanent, since, as is well known, 

 the silver pictures of a comparatively late date sometimes be- 

 come almost obliterated. Of the several novel methods re- 

 ferred to, the first is the so-called carbon process, as devised 

 especially by Mr. J. W. Swan, and familiar to all photogra- 

 phers. The autotype process of Mr. Johnson is said to be es- 

 sentially the same in principle. The most satisfactory meth- 

 ods, however, are those in which light is not required at all for 

 the reproduction of successive impressions from the original 

 negative, this being the case in the Albertype and other meth- 

 ods. The Woodbury process also is especially mentioned as 

 being extremely simple, and, at the same time, perfect in its 

 work. In this a thin sheet of gelatine is sensitized by im- 



