1871.] Proceedings of the Asiatic Society. 243 
separately dissolved in about 1 ounce of hot water, then mixed and 
added very gradually, and with constant stirring to the gelatine 
dissolved in the remaining 6 ounces of hot water, The mixture is 
then filtered through coarse cloth and poured on the plates. Should 
any air bubbles be formed they may be removed with the point of 
a pen-knife. The gelatine soon sets and as soon as I find the film 
is firm, I turn the plates face downwards and place them out to dry 
in the open air on suitable supports. They dry in from 12 to 24 
hours or longer according to the state of the atmosphere. I think 
the plan I have here adopted of preparing the gelatine film with- 
out the addition of the sensitive bichromate is advantageous in 
many ways. It enables the plates to be dried in the open air, 
quickly and evenly and I find that when turned face downwards 
very little dust settles on them ; another advantage is that a stock 
of plates may be prepared and kept till required to be sensitised for 
use. After sensitising the plates dry very quickly and heat may be 
used without any fear of the film becoming dissolved and flowing 
off the plate. I tried Mr. Edwards’ process of mixing together the 
gelatine, chrome alum and bichromate of potash according to his 
published formula, but I found that the plates so prepared took a 
very long time to dry and required to be kept carefully level in the 
drying box, besides this there were other disadvantages which Jed 
me to abandon the use of chrome alum and substitute tannin with 
which I had made some experiments so long ago as 1866. 
When the plates are thoroughly dry I immerse them in a solution 
of bichromate of potash about 1 oz. of the salt to 20 ounces of water 
and then place them in a drying box. As the gelatine is quite 
insoluble there is no necessity for keeping the plates level in this 
second drying and if necessary heat may be used. The plates dry 
- in 2 or 3 hours and are then ready for use. I expose under a 
reversed negative for about 10 minutes in the sun for a clear line 
subject and about half an hour for a subject in half tone accord- 
ing to the density of the negative. When sufficiently exposed 
I remove the negative and expose the back of the sensitive plate to 
light for a few minutes in order to thoroughly harden the under 
surface of the gelatine film and prevent swelling and it from 
puckering up during the printing. ~The plate is then thoroughly 
