Memoranda on poisons / [Thomas Hawkes Tanner].

  • Tanner, Thomas Hawkes, 1824-1871.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Memoranda on poisons / [Thomas Hawkes Tanner]. Source: Wellcome Collection.

    146/174 (page 134)
    aud is a very delicate test, taken in conjunction with others, of its presence. (it.) The Silver Test.—Kitrate of silver yields, with liydroc5’anic acid or cyanide of potassiuin, a vhite clotted precipitate (cyanide of silver) (a) insoluble in cold but (/i) soluble in boiling nitric acid. If this precipitate bo well dried and (c) heated, cyanogen gius will be given off, which may be known by (d) its burning with a purplish flame. Tliis test is very delicate. (6.) The Iron Test.—Of the liquid collected in the receiver above mentioned, or of the suspected acid liquid, carefully neutralised by caustic potass, a portion is to bo taken, and to this is to bo added a small quantity of a solution of sulphate qf iron. A dirty brownish or greenish precipitate will fall, consisting of a mixture of the oxide of iron and Prussian blue. On adding a few drops of dilute sulphuric or hydrochloric and, and thus dissolving the oxides, the intense colour of Prussian blue will immediately be made clear should hydi'ocyanic acid be present. (c.) The Sulphur Test.—One of the most useful tests for pnissic acid, whether in the fluid or volatile state, is the so-called sidphtir or Liebig's test. It is best adapted for detecting the acid in a state of vapour, and to this end, (a) a drop of yellow sulphide of ammonium in a watch- glass is held inverted over the suspected liquid, which may be wanned by the hand to facilitate the evolution of the acid. In this position the watch-glass should bo allowed to remain for some little time, till it has nearly dried, after which (&) a drop of a neutral solution of sulphate of iron is to bo added, which will give rise to a blood-red colour complehdy discharged by corrosire, sublimate. The colour produced by the persalts of iron