a, Flask containing the suspected fluid, dilute sulphuric acid, and zinc.
b, Funnel.
c, Tube containing the copper-leaf or c.-riband, and heated by the lamp d.
e, Support.
f, Capillary end of tube c, with the gas inflamed.
Lassaigne’s Test. (Adopted by the French Academy.) This consists in passing the gas generated in the suspected liquid, through a solution of nitrate of silver. (See engr.) When arsenic is present black flocculi of metallic silver are deposited, and arsenious acid remains in solution mixed with nitric acid and some arsenide of silver. The filtered
liquor, treated with ammonia, will now give a characteristic yellow precipitate of arsenite of silver; or a little dilute hydrochloric acid may be cautiously added to precipitate any remaining nitrate of silver, and the liquid, after filtration, tested for arsenic either in a Marsh’s apparatus, or with any of the liquid tests; or it may be evaporated to dryness, when its arsenious acid will be converted into arsenic acid by the nitric acid present, and will then be found to give the usual brick-red precipitate of arseniate of silver with a solution of the nitrate of that metal. See Marsh’s Test.
a, Bottle containing dilute sulphuric acid, zinc, and suspected fluid.