174 On a new Photo-Lithographic Process. 



Without entering too minutely upon a description of 

 the manipulatory details peculiar to my process, I shall 

 simply give a concise account of the several operations, so 

 far as they are of scientific interest. 



In the first instance a sheet of paper is prepared with 

 albumen in the usual way known to photographers; it is, 

 when quite dry, passed through a copperplate or lithographic 

 press, upon a polished steel or copper plate, by which opera- 

 tion it receives a very smooth and regular surface ; it is then 

 coated on the same side with a solution of gelatine, to which 

 an addition of bi-chromate of potash has been made ; this is 

 then carefully dried in the dark, and again passed through 

 the press to ensure the finest surface. This operation com- 

 pletes the preparation of what I shall call the sensitive 

 paper. Having made a negative of the original map bearing 

 the desired proportions to it, I place a suitable piece of the 

 sensitive paper, just described, under and in close contact with 

 the map, and the whole is exposed to daylight in such a way 

 that the luminous influence passing through the transparent 

 parts of the negative, shall strike directly upon the prepared 

 surface, while the greater part of the paper is protected from 

 its influence by the dark parts of the negative, which cor- 

 respond to the white places on the original map. In the 

 presence of the organic matter, the actinic agency effects the 

 decomposition of the bi-chromate of potash, and the liberated 

 nascent oxygen in all probability re-acts upon the gelatine, 

 altering its chemical characteristics in a peculiar manner. 

 The visible effect after removing the negative is the forma- 

 tion of a picture in brown upon the clear yellow of the 

 paper, corresponding to the transparent portions of the nega- 

 tive, or to the black lines upon the original drawing. 



This positive photographic print is next covered with an 

 even coating of lithographic transfer ink, by passing it 

 through the press face downwards upon an inked-in litho- 

 graphic stone ; the pressure causes the whole of the sensitive 

 surface to lay hold of the ink, and bear away with it an 

 even coating, hiding the brown photographic positive from 

 view. The altered parts of the gelatine which have been 

 exposed to the luminous action appear to be possessed of a 

 certain amount of affinity for the grease of the ink, so that 

 they will be found to retain it with considerable tenacity. 



The next operation is to coagulate the albumen which still 

 exists under the prepared surface ; this is done by floating 

 it upon boiling water, with the paper-side downwards. A 



