1878.] io the Beproduction of Maps and Finns. 93 



tical working. It is much to be regretted that owing to the many difficulties 

 met with in manipulating the gelatine films in the hot damp climate of 

 Calcutta, and in getting printers with the special artistic skill required to 

 produce the best results, our efforts have not been quite successful, and, as 

 photozincogra^Dhy is found more convenient for most of the work passing 

 through the office, the photocoUotype process has not been brought into 

 general use. 



As the process previously described in the Proceedings has since then 

 been modified and is, I know, exceedingly good for line work, the following 

 description of the manipulations, extracted from the Annual Reports of the 

 Surveyor General's Office for 1871-72 and 1872-73, may prove of interest, 

 especially as the working details of few of the other processes have been 

 published. 



The printing plates are of plate glass, about f or half an inch in thick- 

 ness, evenly ground on one side with fine sand. When required for use 

 they are thoroughly cleaned to remove all grease, and then carefully levelled. 

 The composition of the gelatine coating is as follows : — 



Gelatine, 1 ounce. 



Glycerine, 1 dram. 



Distilled water, 6 ounces. 



= { 



C. 



Albumen,* 1 ounce. 



Distilled water, 1 ounce. 



Tannin, 10 grains. 



\ Water, (in hot weather, Spirits of wine,) ... 1 ounce. 

 The above quantity will be sufficient for two square feet of plate. 

 As soon as the gelatine in solution A is quite dissolved, B is added and 

 then C is poured in gradually with constant stirring. The whole is strained 

 through two thicknesses of cotton cloth and poured evenly over the plates 

 on the ground side, any air bubbles being carefully removed. The plates 

 are then covered over with a light paper cover, to prevent dust falling on 

 them, until they are set, when they may be removed into the open air and 

 turned face downwards to dry. Or they may be dried with gentle heat in 

 a drying box, but too quick drying is to be avoided because the gelatin© 

 films will dry unevenly. 



When the plates are dry, they may be put away till required or 

 sensitised in a bath of — 



Bichromate of Potash, 1 part. 



Water, 20 parts. 



They are allowed to remain in this for 5 minutes, then removed to a 

 drying box and dried with a gentle heat. When dry, the deposit at the back 

 of the plates, and any inequalities at the corners of the gelatine film arq 

 * 30 grains of carbolic soap may be used instead of thu albumen. 

 13 



