THE RISE AND PROGRESS OF PHOTOGRAPHY. 155 
and could not be washed out again. In this and various other 
interesting experiments he may be said to have been the father 
f all the various processes having for their base bichromate of 
e 
potash and gelatine. 
gelatine coating and reach the paper, all was good so far as 
washing away the insoluble parts was concerned, but the image 
ined n 
the picture through the transparent medium, and, after 
necessary exposure to light, washed away the soluble portions 
i i i attached 
glass previously coated with collodion; in this manner he was. 
enabled to separate it from the glass, expose it to light, and 
remount it again for development. This he called the tissue, and 
greatly improved his. 
y 
Support of paper. r many important improvements and the 
establishment of the single and double transfer, Mr. R. Sawyer, 
im 1874, introduced his flexible support for the purpose of cl 
