A Manual of the Chemistry of the Carbon Compounds

336 THE CHEMISTRY OJP
water, and crystallizes in long, shining yellow needles; by heat and
by percussion it explodes with an extraordinary violence, and is
therefore used for the preparation of explosives,
The picrates of sodium, ammonium, barium, and silver are readily
soluble in. water.
Ethyl pkrate CjH^NO^OCgHj is produced by the action of ethyl
iodide upon dry silver picrate. It crystallizes in long, pale-yellow
needles, which oa heating first melt, and then decompose with a
slight explosion.
By the action of phosphorus pentacbloride upon picric acid, triniirocMorobenzene
CjHiNOjJgCl is obtained, a crystalline solid, having
an aromatic smelL Ihis compound has been also called picryl chloride,
because it is decomposed by water, analogous to other acid chlorides,
into picric acid and hydrochloric acid.
This reaction shows how the character of an aromatic compound is
modified when hydrogen is replaced by nifcroxyL Whilst monochlorobenzene
is not acted on by caustic potash, its trinitro-couipound
is readily decomposed by water.
Ttimlro-amidobanzene, or JHeramide CjHJNO-JgBHj, is produced
by acting with ammonium carbonate on picryl chloride, or by heating
ethyl picrate with alooholic ammonia. It crystallizes from glacial
acetic acid in glistening yellow plates, melting at 187°. On heating
it stronger, it decomposes without explosion ; and, by boiling it with
caustic potash, it yields ammonia and potassium picrate.
Picric acid combines with aromatic hydrocarbons, forming compounds
which are distinguished by their characteristic colours
or crystalline forms. This acid is, therefore, often used for the
detection or separation of such hydrocarbons. Thus on dissolving
picric acid in not benzene, the compound C6H0 -f- C0H2(NOg).OH
separates out on ocoling in pale-yellow transparent crystals, melting
at 149°; it dissolves, without decomposition, in alcohol and ether;
but when exposed to the air, benzene is slowly given off, whilst;
alkalis decompose it at once,
Isopurpitric Add, or Picramjamie Add CQHJNJO,.—The potassium
salt of this acid is formed by dissolving picric acid in a solution of
potassium cyanide -,—