§ 270. The action of both sodic and ammonic cyanides is precisely similar to that of potassic cyanide. With regard to ammonic cyanide, there are several experiments by Eulenberg,[263] showing that its vapour is intensely poisonous.
[263] Gewerbe Hygiene, p. 385.
A weak stream of ammonic cyanide vapour was passed into glass shades, under which pigeons were confined. After a minute, symptoms of distress commenced, then followed convulsions and speedy death. The post-mortem signs were similar to those produced by prussic acid, and this substance was separated from the liver and lungs.
§ 271. With regard to the double cyanides, all those are poisonous from which hydric cyanide can be separated through dilute acids, while those which, like potassic ferro-cyanide, do not admit of this decomposition, may be often taken with impunity, and are only poisonous under certain conditions.
Sonnenschein records the death of a colourist, after he had taken a dose of potassic ferro-cyanide and then one of tartaric acid; and Volz describes the death of a man, who took potassic ferro-cyanide and afterwards equal parts of nitric and hydrochloric acids. In this latter case, death took place within the hour, with all the symptoms of poisoning by hydric cyanide; so that it is not entirely true, as most text-books declare, that ferro-cyanide is in no degree poisonous. Carbon dioxide will decompose potassic ferro-cyanide at 72°-74°, potass ferrous cyanide being precipitated—K2Fe2(CN)6. A similar action takes place if ferro-cyanide is mixed with a solution of peptone and casein, and digested at blood heat[264] (from 37° to 40° C.), so that it is believed that when ferro-cyanide is swallowed HCN is liberated, but the quantity is usually so small at any given moment that no injury is caused: but there are conditions in which it may kill speedily.[265]
[264] Autenrieth, Arch. Pharm., 231, 99-109.
[265] The presence of ferro-cyanide is easily detected. The liquid is, if necessary, filtered and then acidified with hydrochloric acid and a few drops of ferric chloride added; if the liquid contains ferro-cyanide, there is immediate production of Prussian blue. It may happen that potassic or sodic cyanide has been taken as well as ferro-cyanide, and it will be necessary then to devise a process by which only the prussic acid from the simple cyanide is distilled over. According to Autenrieth, if sodium hydrocarbonate is added to the liquid in sufficient quantity and the liquid distilled, the hydric cyanide that comes over is derived wholly from the sodium or potassium cyanide. Should mercury cyanide and ferro-cyanide be taken together, then this process requires modification; bicarbonate of soda is added as before, and then a few c.c. of water saturated with hydric sulphide; under these circumstances, only the hydric cyanide derived from the mercury cyanide distils over. If the bicarbonate of soda is omitted, the distillate contains hydric cyanide derived from the ferro-cyanide.