THE RISE AND PROGRESS OF PHOTOGRAPHY. 153 
will begin with the gun cotton. This Sey: rrerisens is ia by 
saturating ordinary cotton wool, certai or paper, 
in a mixture of nitric and sulphuric aah ie anith it is well 
washed to free it from all traces of acid. and allowed to 
It is then dissolved in a mixture of alcohol and ether, and forms 
a glutinous solution of he consistency of oil; ¢ ertain bodidig and 
The iodides and bro s now combine with the silver and 
by double decomposition an iodide and bromide of silver with 
an excess of nitrate of silver in solution. This is then 
exposed to the action of light in the ca obscura, when a 
cyanide of potassium or ace ere 
Perfect negatives being now easily a it os necessary 
to use another and more perfect paper to rec the positive 
image. A smooth and finely grained tases was chosen an 
prepared by laying on its — a solution of albumen in 
which was i 
These e pri 
and fixed in hyposulphite of soda; these are called silver prints, 
and the process is the one in actual use where only small numbers 
of proofs are required. 
of “ was @ sara aren in the now ninsen stage 
photo hy, but progression, the natural orde hings, 
brought Sembee aid, and as aie and uncertainty came 
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