238
ELEMENTS OF MATERIA MEDICA.
ride of mercury, which remains in the retort, and two equivalents or 54parts of hydrocyanic acid, which distil over.
INGREDIENTS REACTING. RESULTS.
2 eq. Hydrochi'. Acid 74 J | chltridl" ~2 eq. Elydrocyanic Acid 54
1 eq. Bicyan' 1 ' 1 . Mercury 254 ^ eq- Cyanogen ^ { e q. Bichloride Mercury 274
(i d.) By the action of tartaric acid on cyanide of potassium. —Thisprocess was proposed by Dr. Clarke, and adopted by Mr Laming. Theformula of the latter is the following:—22 grains of the cyanide ofpotassium are to be dissolved in 6 fluidraclims of distilled water, and tothis solution are to be added 50 grains of crystallized tartaric acid,dissolved in 3 fluidraclims of rectified spirit. One fluidrachm of thedecanted clear liquor contains one grain of pure hydrocyanic acid.
The objections to this process (which, however,has several advantages)are the trouble and expense of procuring pure cyanide of potassium,and the liability of the salt to undergo spontaneous decomposition.
The theory of the process is the following:—Two equivalents or 150parts of crystallized tartaric acid, one equivalent or 9 parts of water, andone equivalent or 66 parts of cyanide of potassium, react on each other,and produce one equivalent or 189 parts of the crystallized bitartrate ofpotash, which precipitates, and one equivalent or 27 parts of hydrocyanicacid, which remains in solution.
INGREJJIENTS REACTING. ' RESULTS.
1 eq. Water. 9
1 eq. Cyanide Pot". 66 j | e< P Cyanogen . 26(1 eq. Potasium . 40f 2eq.DryTart.A d . 1322eq. Crys.Tart'. A' 1 .150 jl eq. Water . . 9
tl eq. Water . . 9
c 1 eq. Hydrogen . 1
(1 eq. Oxygen . . 8
leq.Pot h .48
1 eq. Hydrocya". A d . 27
leq.Crys.Bitar c .Pot h . 1891 eq. Water. 9
Properties, (a.) Of anhydrous hydrocyanic acid. —Anhydrous hydro-cyanic acid is a solid at 0° F. (some state at 5° F.), having then theappearance of crystallized nitrate of ammonia : it readily melts, forminga limpid, colourless liquid, with an intense and peculiar odour; itstaste is at first cool, then hot; at 45° its sp. gr. is (P7058, and at 64| is0'6969. In this state it is exceedingly volatile: a drop placed on paperfreezes by its ovvn evaporation. It unites with water and alcohol inevery proportion. At 79° or 80° F. it boils, forming hydrocyanic acidvapour, which is combustible ; and when mixed with oxygen, explodes.Two volumes of the vapour require two and a half volumes of oxygen gasfor their complete combustion. The products are two volumes of car-bonic acid gas, one volume of nitrogen, and one volume of aqueousvapour.
Anhydrous hydrocyanic acid undergoes speedy decomposition. Dr.Christison says he has kept it unchanged for a fortnight in ice-coldwater.
(b.) Of dilute hydrocyanic acid. —Dilute or medicinal hydrocyanic acidis a colourless, transparent liquid, having the taste and smell of thestrong acid, but in a lesser degree. Heated in a tube it gives off a com-bustible vapour.
Composition. —The ultimate constituents of pure hydrocyanic acidare carbon, nitrogen, and hydrogen.