ON THE VOLATILITY OF FIXED SALTS. 
259 
gen. It is at this moment, and during the whole time of 
the formation of nitrous vapors that the volatilization of the 
silver takes place, and the designs are produced. After 
twenty or forty minutes of exposure, according to the shade 
wished for, the papers are withdrawn and replaced by 
others. s When the solution of the silver is complete, and all 
re-action has ceased, the liquor is evaporated and crystallized; 
the nitrate of silver obtained, is used in commerce in large 
quantities, so that papers are thus prepared without any 
expense. 
According to the length of time the paper is submitted to 
the vapors of the silver, and according to the distance from 
the point of emission of the vapors at which the papers are 
placed, so a plain colored paper or a dotted one is obtained, 
the latter much resembling granite. If white designs are 
required, such as leaves, laces, &c,, it is only necessary to 
place on the paper cut pieces of paper of the designs wished 
for before submitting it to the vapors. The Society has 
seen several specimens of this class, and amongst others the 
leaves of several plants, and some lace patterns, which were 
well executed. 
The papers thus prepared are very strong, and they do 
not undergo and change by exposure to the light and air ; 
this may readily be conceived as silver is the coloring prin- 
ciple. In what state does the silver exist in these papers ? 
Is it in the metallic state, in the state of liberated oxide, or 
combined with organic matter ? M. Larocque has made 
several experiments with a view to solve this question, but 
the results have not enabled him to decide definitely. 
Nevertheless, he appears to be in favor of the last opinion, 
for it seems to him difficult to account in any other way for 
the decoloration of the papers thus acted on by the simple 
contact of a solution of hyposulphite of , soda, iodide, bro- 
mide, or cyanide of potassium. This latter salt, especially, 
easily removes the stains, of whatever age they may be, 
which the nitrate of silver produces on organic tissues. 
