Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

SILVBE FULMINATE 159
concentrated solution of sodium nitrite (3-5 g.) is added. Without
further cooling 4 2\f-sulphuric acid is run in from a dropping funnel
until the solution, which is at first deep red, has just become yellow
and does not yet turn potassium iodide-starch paper blue. The
mixture is now extracted twice with ether and the aqueous layer is
again cooled. Sulphuric acid is again dropped in until the evolution
of nitrous acid becomes distinct and the solution is then again made
so strongly alkaline with 52V-sodium hydroxide solution, that a
deep orange colour results. Once more the solution is acidified to
such an extent that nitrous acid cannot yet be detected, and is again
extracted twice with ether. The combined etKer extracts are dried
for two hours over calcium chloride in a vessel kept on ice. The
ethereal solution is now transferred to a small round flask and the
solvent removed by distillation with a capillary in vacuo on the water
bath at 15°-20°. A residue consisting of about 1 g. of well-crystallised
pale yellow methylnitrolic acid remains. The preparation decomposes
in the course of a few hours. Test its behaviour towards
alkalis.
Silver Fulminate. 1 —Freshly-prepared methylnitrolic acid (0-5 g.)
dissolved in 4 c.c. of water is heated to boiling in a wide test tube over
a naked flame with 1 c.c. of 52V-nitric acid (concentrated nitric acid
of density 1-4 diluted with an equal volume of water) and 4 c.c. of
10 per cent silver nitrate solution. After a short time the reaction
begins, a vigorous evolution of gas (NO) occurs, and crystalline
silver fulminate is precipitated. Boiling is continued for a few
minutes longer with constant shaking. The mixture is then cooled
and the product filtered at the pump and washed with water. On a
small piece of porous plate a small sample weighing about 10 mg. is
dried without rubbing and its shattering power is tested in the flame
and under a blow from a hammer. (Wear goggles.)
While still moist the bulk of the material is transferred to a test
tube ; even in the moist condition pressing with a metal spatula or
other hard object is to be avoided. Then 2 c.c. of concentrated
hydrochloric acid are poured into the test tube, when the odour of
free fulminic acid can be perceived. This odour so closely resembles
that of hydrocyanic acid as to make confusion possible. After half
an hour the contents of the test tube are heated for a short time in the
boiling water bath, 4 c.c. of water are added, silver chloride is
removed by nitration, and the nitrate is evaporated to dryness on
1 Ber., 1907, 40, 419.