M. TECHNOLOGY. 515 



erine. The block is then ready for the printer. Another 

 method consists in using as a substitute metallic substances, 

 as tin, brass, or zinc, preparing them first by rubbing with a 

 solution formed of one ounce of hydrochloric acid, one fourth 

 of an ounce of zinc, and one drachm of glacial acetic acid. 

 After the plate has received the impression from the stone or 

 wood in an ordinary lithographic press, or by means of a 

 "transfer," the ink thereon is dried by heating the plate, 

 which is afterwards plunged while still hot into cold water 

 this latter operation being supposed to confer permanency 

 upon the impression. The ordinary ink is used in this pro- 

 cess, which appears to consist, in reality, of "soldering" the 

 design on the plate and burning it in. 18 A, December 1, 

 1871,266. 



WINDOW PHOTOGRAPHIC PROCESS. 



A new and quite peculiar photo-lithographic process, lately 

 announced by Window, bids fair to become of much practical 

 value. For this, white paper is coated with a mixture of gel- 

 atine and birchromate of potash, and, after drying, illumina- 

 ted under a negative. The soluble chrome salt is then washed 

 out with water. If the wet picture is now touched with 

 printers' ink, the portions corresponding to the light lines of 

 the negative take up the black. This is based upon the pe- 

 culiarity of gelatine of resisting the fatty blacks, even in thin 

 sheets, and also the fact that these blacks are readily taken 

 up by the lithographic stone. A piece of gelatine paper is 

 rendered sensitive in the ordinary manner in a bath of bichro- 

 mate of potash, and illuminated under a positive matrix of 

 the object to be lithographed. After a sufficient illumina- 

 tion the paper is immersed some seconds in water, and laid 

 with the gelatine side down upon a clean, polished litho- 

 graphic stone, and then rubbed several times with a rubber 

 pad to press out the superfluous water. A few minutes after 

 warm water is poured on, of the temperature of about 97, 

 and the picture developed exactly like a carbon print. The 

 paper becomes gradually loosened, and with a little action 

 of the warm water can be completely removed. Warm wa- 

 ter is then poured carefully over the side to separate all tho 

 remaining soluble gelatine. 



The picture thus obtained is naturally a negative, because 



