Mydaleine is very poisonous. Small quantities injected into guinea-pigs cause dilatation of the pupil, an abundant secretion from the nose and eyes, and a rise of temperature. Fifty mgrms. cause death. The post-mortem appearances are not distinctive; the heart is arrested in diastole; the intestines and bladder are contracted. In cats it causes profuse diarrhœa and vomiting.
§ 671. Guanidine.—Guanidine may be considered to have a relation to urea; for, if the oxygen of urea is replaced by the imide group NH, guanidine originates thus:—
Hence guanidine from its structural formula is a carbodiamidimide. Guanidine may be formed by the action of oxidising agents, such as potassic chlorate and hydrochloric acid, on guanine; or by heating amide cyanide with ammonium chloride, and so forming guanidine chloride. It is also produced from the oxidation of albumin. When boiled with baryta-water it decomposes into urea and ammonia. It combines with acids to form salts; the gold salt, CH5N3HCl,AuCl3, is in the form of long yellow needles, with difficulty soluble in water. Guanidine nitrate, CH5N3HNO3, is also almost insoluble in cold water and similar to urea nitrate. By dissolving equivalent parts of phenol and guanidine in hot alcohol, triphenylguanidine is formed; on adding picric acid to a solution of triphenylguanidine, phenylguanidine picrate, CH2Ph3N3C6H2(NO2)3OH, is formed, and falls as a precipitate of slender needles, melting-point 208°; this picrate is very slightly soluble, 1 part dissolving in 12,220 parts of water at 15°. Guanidine is poisonous.[667]
[667] O. Prelinger, Monatsb., xiii. 97-100.
A method of separating guanidine from urine has been worked out by Gergers and Baumann.[668] The principle of the method is based upon the fact that guanidine is precipitated by mercurous oxide. The urine is precipitated by hydrate of baryta, the precipitate filtered off, the alkaline filtrate neutralised by hydrochloric acid, and the neutral filtrate evaporated to a syrup on the water-bath; the syrup is exhausted by absolute alcohol, and the alcoholic solution filtered; this filtrate is freed from alcohol by distillation, the alcohol-free residue dissolved in a little water, shaken up with freshly precipitated mercury oxide, and allowed to stand for two days in a warm place; the precipitate formed is collected, acidulated with HCl and treated with SH2; the mercury sulphide thus obtained is separated by filtration, the filtrate evaporated, and the residue dissolved in absolute alcohol. This solution is precipitated by platinum chloride, filtered, separated from any platinum ammonium salt, and evaporated to a small volume. After long standing the guanidine salt crystallises out. The best method to identify it appears to be, to ascertain the absence of ammonia and of urea, and then to gently warm the supposed guanidine with an alkali, which breaks guanidine up into ammonia and urea, according to the following equation:—
NH=C(NH2)2 + H2O = NH3 + CO(NH2)2.