XI. “With peroxide of hydrogen, natural blood gives effervescence from escape of oxygen, but no discoloration. Blood containing HCN gives a brown colour, the spectroscopic bands disappearing, and no effervescence.” (Schönbein.) Hæmatocrystallin, the colouring matter of the blood corpuscles, combines, in fact, with HCN, giving a dark coloured compound which appears to be crystallizable and definite in composition (Hoppe Seyler), does not act as a carrier of oxygen like the natural hæmatocrystallin, and possesses a distinct spectrum (see Thudichum, Chem. Physiology). The blue masses in the blood described by Ralph (Journ. Microsc. Science, Oct. 24, 1866) have not been found by others.
XII. Mercurous nitrate gives at once with HCN solutions, a black deposit of metallic mercury, and a solution of mercuric cyanide. With calomel, a similar reaction takes place according to Allen, but I have found that the solution is not deodorized even by large excess of calomel, the odour becoming stronger and more pungent than the original HCN. On evaporating, mercuric chloride is left. Probably some cyanogen chloride is formed. The odour is so much intensified that it might be of use as a test. In view of the possible administration of calomel, the reaction is interesting.
Of course it will not be necessary to employ all these methods. The odour, and the silver, Prussian blue, and “sulphur” tests will be sufficient. I would suggest a form of apparatus by which all the latter could be obtained from the original substance without distillation in a retort.
A shallow beaker or glass jar is closed by an india-rubber stopper, through two holes in which are passed glass rods ending in glass spoon bowls bent at right angles, so as to be horizontal when mounted. The bowls should be one inch in diameter, and will have to be specially made. In the first bowl a few drops of silver nitrate are placed, in the second a little potash. The apparatus is put in a warm place for six or eight hours, then the two rods are removed, a third rod substituted, its bowl containing a drop or two of yellow ammonium sulphide, the other hole plugged, and the apparatus put back in the warm place for two or three hours more. The first bowl will have the silver cyanide, the second should be treated with ferric and ferrous salt and hydrochloric acid for Prussian blue (vide), the third evaporated and ferric chloride added for the sulphocyanide test. This arrangement prevents loss of HCN by volatilization, and also, with a little care, avoids any danger of the reagent dropping back into the solution. The three rods cannot safely be placed in together, as the sulphide vapour would blacken the silver.
For the modifications in testing necessitated by the presence of mercury, &c., see under the different Salts.
SALTS.
Hydrocyanic acid combines with bases to form the cyanides, which may be thus grouped:—
A. Cyanides of the Alkalies (potassium, sodium, ammonium), and of the Alkaline Earths (barium, strontium, calcium, magnesium). These are all soluble in water, are alkaline to test paper, and are decomposed by all acids, even carbonic, hence they exhale an odour of HCN, and are nearly as poisonous as prussic acid itself. If they are present, the stomach contents must be alkaline. The only member of this group likely to be met with is
Potassium Cyanide, KCN. Broken opaque white lumps, or small crystals, deliquescent, smelling strongly of HCN, soapy to the feel, often containing much carbonate, and therefore effervescing with acids, easily fused by heat to a clear liquid, very soluble in water, less in alcohol. Used for removing silver stains in the form of “cyanogen soap,” but very dangerous, as a cut or scratch may cause absorption, and even the unbroken skin, according to Allen, may absorb enough to cause symptoms. Its aqueous solution decomposes spontaneously into formiate of potassium, ammonia, and a brown substance. Its taste is bitter and acrid, causing constriction and a burning heat in the throat. It is very strongly alkaline. Distilled with dilute acids it gives off all its HCN. It easily responds to the other tests. In a case of poisoning investigated by Dr. Bernays, a piece of potassium cyanide was found in the deceased’s mouth, which was much inflamed by its acridity. The alkali being strong, and the acid weak, cyanide of potassium has most of the effects of an alkaline irritant.
The potassium may be found by incinerating a portion of the substance and testing for it in the ash. Taylor (Med. Jurisprudence) improperly says that the salt itself (cyanide of potassium) may be recovered from the organs by incinerating them in close vessels and treating the ash with water. I have already mentioned that cyanide would be formed in this way from the organic matters themselves, even if not originally present.