2-39
Carbion .
Eq.
. . 2 .
Eq.Wt.
. . . 12 . .
Theory.
. . 44*4 »
Carbon vapour
Vols.
1 or 2 .
Sp. Gr.
. 0*8333
Nitrogen
. . 1 .
. . . 14 . .
. 51-9 .
. . . 51-85
Nitrogen gas. .
. . . 1 .
. 0-9722
Hydirogen
. . 1 .
. . . 1 . .
. . 3-7 .
. . . 3-70
Hydrogen gas .
. . . 1 .
. 0-0694
Hydirocy c .
A d . 1 .
... 27 . .
. 100-0 .
. . . 100-00
Hydrocyanic vapour . 2 .
. 0-9374
But it is more usual to regard this acid as a compound of hydrogen andcyanogen, the latter substance being a bicarburet of nitrogen. On thisview the composition will be as follows:—
Eq.
Cyanogen.1 .
Hydirogen.1 .
Eq.Wt.
. . 26 . .
. . 1 . .
Per Cent.
. . 96-3
. . 3-7
Cyanogen gas ....Hydrogen gas ....
Vols.
. . 1 . .
. . 1 . .
Sp. gr.. 1-8055
. 0-0694
Hydrocyanic Acid. . 1 .
. . 27 . .
. . 100-0
Hydrocyanic vapour .
. . 2 . .
. 0-9374
The following diagrams illustrate the composition as well as theproducts of the combustion of the gaseous acid when exploded withoxygen gas:—
Constituents. Eq. Vol. Before combustion. After combustion.
Ilydr.
1 eq.Hydro-cyanicacid va-po ur —7
1 eq.
Carb. Ad.= 22
1 eq.Nitrog*.
= 14
1 eq.
Carb. Ad.= 22
1 eq.
Aq. vap.
= 9
1 eq.Hydro-cyanicacid va-pour = 27
2 eq.Oxygen= 16
1 eq.
Oxyg. = 8
2 eq.Oxygen= 16
Strength of the Dilute Acid. —In the Pharmacopoeia , hydrocyanicacid is directed to be prepared of such a strength that 100 grains of itwill exactly precipitate 12'7 grains of nitrate of silver dissolved in water:—the precipitate, which is cyanide of silver, should weigh 10 grains.Hence the dilute acid should consist of—
Real Hydrocyanic Acid. 2*0
Water. 98*0
Dilute Hydrocyanic Acid (Ph. L.).100*0
Purity. —Dilute hydrocyanic acid should be perfectly colourless;decomposed acid is frequently, but not invariably, coloured. Itshould be vaporizable by heat: this character shows the absence offixed impurities. The presence of metallic matter is recognized byhydrosulphuric acid, which has no effect on the pure acid. If the acidstrongly redden litmus, it must contain some other acid, most probablythe sulphuric or hydrochloric. The presence of any foreign acid iseasily determined by the hydrargyro-iodo-cyanide of potassium. This saltis easily formed by adding a concentrated solution of bicyanide ofmercury to a solution of iodide of potassium: a precipitate of white orpearly crystalline plates immediately takes place: these are the salt inquestion. If a small portion of this salt be placed in diluted hydrocyanicacid, no change is observed unless some foreign acid be present: inthe latter event the red biniodide of mercury immediately makes itsappearance. For this test we are indebted to Dr. Geoghegan (DublinJournal, Nov. 1835). Sulphuric acid may be detected by a solution ofchloride of barium: hydrochloric acid by nitrate of silver, which forms