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To Obtain Cyanic Acid

Distill dry cyanuric acid, or cyamelide, in a retort, acid. This test may be applied by spreading a single drop of solution of potassa over the bottom of a white saucer or porcelain capsule, and inverting it over another vessel of the same size containing the matter under examination. After 2 to 5 minutes remove the upper capsule; add to the potassa upon it, a and collect the product in a well-cooled resingle drop of a solution of sulphate or tinc-ceiver. It is also formed when cyanogen ture of iron, and expose it to the air for a few is transmitted over carbonate of potassa seconds. Next add 1 or 2 drops of dilute heated to redness; a cyanate of potassa resulphuric acid, when a blue color will be developed if hydrocyanic acid is present in the matter tested.

Nitrate of silver gives a white clotty precipitate, soluble in boiling nitric acid; and which, when dried and heated in a test tube, evolves fumes of cyanogen, which burn with a violet or bluish colored flame. A watch glass, moistened with this test and inverted over matter containing hydrocyanic acid, becomes opaque and white from the formation of cyanide of silver. sults.

Or: Pass a current of sulphuretted hydrogen gas through water in which cyanate of silver is diffused. The sulphuretted hydrogen must not be passed so long as to decompose all the cyanate of silver; for then the cyanic acid is converted into other products by the excess of the sulphuretted hydrogen. 3954, Hydroferridcyanic Acid.

This is sometimes written hydroferricyanic acid, and is a compound of ferridcyanogen and hydrogen. With the oxides of metals

Liebig's test is considered the most delicate. this acid forms FERRIDCYANIDES; the ferrid- Moisten a watch-glass or porcelain capsule cyanide of potassium is the red prussiate of with 1 or 2 drops of yellow hydrosulphuret of potash used in the arts. ammonia; invert it over the matter as before, 3955. To Obtain Hydroferridcyanic and after a few minutes dry it with a gentle Acid. Prepared by decomposing recently heat. A glass rod dipped in a solution of a precipitated ferridcyanide of lead by sulpersalt or sesquisalt of iron, drawn over the phuretted by hydrogen, or by sulphuric acid glass, will form a blood-red streak if the carefully added. A yellow solution is thus smallest quantity of hydrocyanic acid is pres- obtained, which yields a deep brown powder ent. (Cooley.) when evaporated by heat, or yellow crystals A 3951. Test for the Strength of Prus- by spontaneous evaporation. sic Acid. For estimating the strength of 3956. Hydroferrocyanic Acid. the commercial acid the following plan, pro- peculiar compound of cyanogen, hydrogen, posed by Dr. Ure, will be found very exact and iron, discovered by M. Porret, and called by him ferrochyazic acid. It consists of 3964. Perchloric Acid. A colorless white or yellowish white crystals, soluble in liquid of about 1.65 specific gravity, which water and alcohol. With metallic oxides it fumes slightly in the air, attracts moisture, combines to form FERROCYANIDES or PRUS- and distills unchanged at about 392° Fahr. SIATES. The ferrocyanide of potassium is (Cooley.) With bases it forms PERCHLOthe yellow prussiate of potash of commerce. RATES.

3957. To Obtain Hydroferrocyanic