“Care must be taken that on boiling, the weak acid reaction must be retained, and that this manipulation only lasts a few minutes.
“The insoluble portion is filtered off, and the filtrate evaporated, either in the gas-oven or on the water-bath, to syrupy consistency. If the substances are offensive, as alcoholic and watery extracts of flesh usually are, the use of Bocklisch’s simple apparatus (see [diagram]) is to be recommended. The filtrate to be evaporated is placed in a flask provided with a doubly perforated caoutchouc cork carrying two bent tubes; the tube b terminates near the bottom of the flask, while the tube a terminates a little above the level of the fluid to be evaporated. The tube a is connected with a water pump which sucks away the escaping steam. In order to avoid the running back of the condensed water forming in the cooler part of the tube, the end of the tube a is twisted into a circular form. Through the tube b, which has a fine capillary bore, a stream of air is allowed to enter, which keeps the fluid in constant agitation, continually destroying the scum on the surface, and avoiding sediments collecting at the bottom, which may cause fracture of the flask. According to the regulation of the air current, a greater or smaller vacuum can be produced. The fluid, evaporated to the consistency of a syrup, is treated with 96 per cent. alcohol, filtered, and the filtrate precipitated with lead acetate.
“The lead precipitate is filtered off, the filtrate evaporated to a syrup, and the syrup again treated with 96 per cent. alcohol. This is again filtered, the alcohol got rid of by evaporation, water added, the lead thrown down by SH2, and the fluid, after the addition of a little hydrochloric acid, evaporated to the consistence of a syrup; this syrup is exhausted with 96 per cent. alcohol, and precipitated with an alcoholic solution of mercury chloride. The mercury precipitate is boiled with water, and by the different solubility of the mercury salts of certain ptomaines some separation takes place. If it is suspected that some of the ptomaines may have been separated with the lead precipitate, this lead precipitate can be decomposed by SH2 and investigated. I have only (says Brieger) in the case of mussels been able to extract from the lead precipitate small quantities of ptomaines.
“The mercury filtrate is freed from mercury and evaporated, the excess of hydrochloric acid being carefully neutralised by means of soda (for it must only be slightly acid); then it is again treated with alcohol, so as to separate as much as possible the inorganic constituents. The alcoholic extract is evaporated, dissolved in a little water, neutralised with soda, acidulated with nitric acid, and precipitated with phospho-molybdic acid. The phospho-molybdic acid precipitate is decomposed with neutral lead acetate, which process may be facilitated by heating on the water-bath. After getting rid of the lead by treatment with SH2, the fluid is evaporated to a syrup and alcohol added, by which process many ptomaines may be eliminated as hydrochlorates; or they can be converted into double salts (of platinum or gold) for the purpose of separation. In the filtrate from phospho-molybdate, ptomaines may also be found by treating with lead acetate to get rid of the phospho-molybdic acid, and then adding certain reactives. Since it is but seldom that the hydrochlorates are obtained in a state of purity, it is preferable to convert the substance separated into a gold or platinum salt or a picrate, since the greater or less solubility of these compounds facilitates the purification of individual members; but which reagent is best to add, must be learned from experience. The melting-point of these salts must always be taken, so that an idea of their purity may be obtained. It is also to be noted that many gold salts decompose on warming the aqueous solution; this may be avoided by the addition of hydrochloric acid. The hydrochlorates of the ptomaines are obtained by decomposing the mercury, gold, or platinum combinations by the aid of SH2, while the picrates can be treated with hydrochloric acid and shaken up with ether, which latter solvent dissolves the picric acid.
“Considerable difficulty in the purification of the ptomaines is caused by a nitrogenous, amorphous, non-poisonous, albumin-like substance, which passes into all solutions, and can only be got rid of by careful precipitation with an alcoholic solution of lead acetate, in which it is soluble in excess. This albuminoid forms an amorphous compound with platinum, and acts as a strongly reducing agent (the platinum compound contains 29 per cent. platinum). When this albuminoid is eliminated, then the hydrochlorates or the double salts of the ptomaines crystallise.”
§ 651. The Benzoyl Chloride Method.—The fatty diamines in dilute aqueous solutions, shaken with benzoyl chloride and soda, are converted into insoluble dibenzoyl derivatives; these may be separated from benzamide and other nitrogenous products by dissolving the precipitate in alcohol, and pouring the solution into a large quantity of water.[656] Compounds which contain two amido groups combined with one and the same carbon atom, do not yield benzoyl derivatives when shaken with benzoyl chloride and soda. Hence this reaction can be utilised for certain of the ptomaines only. The solution must be dilute, because concentrated solutions of creatine, creatinine, and similar bodies also give precipitates with benzoyl chloride; no separation, however, occurs unless these bodies are in the proportion of five per thousand.