PHARMACEUTICAL NOTICES 
103 
sulphuric acid, by four pounds of mercury, is made to pass 
through this solution. When the reaction is complete, filter 
the liquid and evaporate slowly, so as to crystallize. Decant 
the mother waters, dry the crystals between folds of bibulous 
paper, and preserve in glass stop vials. The apparatus in 
which it is most conveniently made, consists of a matrass in 
which the acid is formed, to the neck of which is adapted two 
tubes, (an S and a connecting tube,) and a couple of Wolf 
bottles; one containing the water to wash the gas, and the 
other the saline liquor. The last should be provided with a 
tube, terminating in a solution of lime, to carry off the excess 
of acid, 
Another and more simple method, according to Berzelius, 
consists in exposing to the air a concentrated solution of sul- 
phuret of sodium, which gradually becomes oxidized. 
Hyposulphite of soda crystallizes in tetrahedral prisms, 
which are colorless, transparent, and at times of large size. 
Some lately exhibited at the laboratory of Messrs. Rosengar- 
ten and Denis were remarkable for their transparency and 
volume. 
Chloride of Gold. 
This is another preparation used in the Daguerreotype, and 
is employed in very minute portions to give color as well as 
fixedness to the image represented upon the plate, which 
otherwise would be effaced by the slightest touch. To 
give the proper color and effect, it is absolutely necessary 
that the gold should be free from the contamination of other 
metals. For this purpose no better means offer than the fol- 
lowing: 
Dissolve gold coin in nitromuriatic acid, then evaporate to 
dryness and subject it to a red heat; afterwards pour upon it 
sufficient nitric acid to dissolve out all the alloy contained in 
the gold coin: filter, and again dissolve in aqua regia, in the 
proportion of one part pure gold to three parts of acid, (formed 
of pure acids.) 
Effect the solution in a porcelain capsule upon a sand bath^ 
