The double salts of the bases and mercury thus obtained, after freeing from the mother liquor, are recrystallized from a solution in water and from the pure product thus obtained the mercury is removed after solution in water, by hydrogen sulfid. The filtrate, after separating the mercury, contains the bases as chlorids (hydrochlorates). The solution of the chlorids is evaporated slowly in (pene) vacuo to a thick sirup and set over sulfuric acid to facilitate crystallization. The hydrochlorates are obtained in this way colorless and in well-shaped crystalline forms.
In a quantitive determination, a small amount of the fine meal is extracted at once with one per cent hydrochloric acid in seventy per cent alcohol, the salts obtained purified as above and weighed.
The following process serves to determine the relative proportions of cholin and betain in a mixture of the two bases.
A definite weight of the chlorids, prepared as directed above, is extracted by absolute alcohol. This treatment dissolves all the cholin chlorid and a little of the betain salt. The alcoholic solution is evaporated and again extracted with absolute alcohol. This process is repeated three times and at the end the cholin chlorid is obtained free of betain. In a sample of cottonseed cake examined in this laboratory the two bases were found present in the following relative proportions, viz., cholin 17.5 per cent, betain 82.5 per cent. Thus purified the cholin is finally precipitated by platinum chlorid. For a description of the special reaction, by means of which cholin and betain are differentiated, the paper cited above may be consulted.
These bodies have acquired an economic interest on account of their occurrence in cottonseed meal, which is so extensively used as a cattle food. It is evident from the relative proportions in which they occur that the less nocuous base, betain, is the more abundant. It is possible, however, that the base originally formed is cholin and that betain is a secondary product.
Experience has shown that it is not safe to feed cottonseed meal to very young animals, while moderate rations thereof may be given to full-grown animals without much expectation of deleterious results. In the case of toxic effects it is fair to presume that a meal has been fed in which the cholin is relatively more abundant than the betain.
389. Lecithin.—Lecithin is a nitrogenous body, allied both to the fats and proteids and containing glycerol and phosphoric acid. Its percentage composition is represented with some accuracy by the formula C₄₂H₈₆NPO₉, or according to Hoppe-Seyler, C₄₄H₉₀NPO₉. It appears to be a compound of cholin with glycerolphosphoric acid. It is widely distributed both in animal and vegetable organisms, in the latter especially in pease and beans.
From a physiological point of view, lecithin is highly important as the medium for the passage of phosphorus from the organic to the inorganic state, and the reverse. This function of lecithin has been thoroughly investigated in this laboratory by Maxwell.[359]
In the extraction of lecithin from seeds (pease, beans, etc.) it is not possible to secure the whole of the substance by treatment with ether alone.[360]
The extraction of the lecithin may, however, be entirely accomplished by successive treatments for periods of about fifteen hours with pure ether and alcohol. This is better than to mix the solvents, since, in this case, the ether having the lower boiling point is chiefly active in the extraction. When the extraction is accomplished by digestion and not in a continuous extracting apparatus the two solvents may be mixed together and thus used with advantage. After the evaporation of the solvents, the lecithin is ignited with mixed sodium and potassium carbonate whereby the organic phosphorus is secured without loss in an inorganic form. Where greater care is desired, the method described for organic phosphorus in soils may be used.[361] The inorganic phosphorus thus obtained is estimated in the usual way as magnesium pyrophosphate.