Technical Chemistry. 419 
for dyeing purposes, it may be prepared by mixing a solation of a picrate 
with sulphate of copper. Picric acid was introduced as a dye about five 
or six years since, by MM. Guinon, Marnas, and Bonney, eminent silk 
dyers of Lyons. Many of the cheap products sold as picric acid are of a 
with a solution of carbonate of ammonia. By this means a crimson 
solution, containing the rosolic acid, is obtained. This solution is then 
evaporated nearly to dryness, during which process ammonia is given off, 
* See the f Mr. Lea on Picric acid and its derivatives, in the late volumes 
of this pt aaa < 
