This salt, when decomposed by the exact quantity of sulphuric acid, yields the free acid, which on evaporation of its aqueous solution may be obtained in the form of an acid, thick syrup. Its salts are mostly soluble in water and crystallisable.

Its calcium salt is thrown down in pearly scales on boiling its cold saturated solution.

Glycerine phosphoric acid occurs as one of the decomposition products of lecithin (§ 697), and is physiologically important from its supposed existence in brain substance, &c.

Salts of Glycerine with Organic Acids. Fats.

692. Glycerine combines with the acids of the CnH2n-10.OH series when heated, water being eliminated. The number of hydroxyl groups replaced depends greatly on the temperature of the reaction and the quantity of acid present.

The neutral salts of the form C3H5(O.CnH2n-10)3 occur in most natural fats, and are in fact, in many, the principal substance. Most solid animal fats, tallow, &c., are composed of glycerine fats of palmitic and stearic acids. As yet no known fat consists entirely of the salt of one acid; they are generally mixtures of several, not only of the above-mentioned series, but also with salts of acids of the oleic series, C3H5(O.CnH2n-30)3. These latter salts confer liquidity (animal oils) or buttery consistency on many fats, according to the extent of their admixture.

Fatty or animal oils also frequently contain acids of still lower hydrogen contents, which oxidise easily on exposure to air, becoming hard and resinified, the same property being imparted in some degree to their glycerine salts, which are hence termed drying oils.

The existence of glycerine salts of mixed acids has no doubt a great influence in causing the variety of animal fats. It appears, for instance, that mutton fat, or sheep tallow, contains a glycerine distearin palmitate, C3H5(O.C18H350)2- (O.C16H310).

To extract fats from organic tissues or substance mechanical pressure, sometimes with elevation of temperature, is generally resorted to, whereby the cells containing the fats are broken. In cases where it is desired to extract the whole amount completely, solvents, like ether or disulphide of carbon, are used. From these the fat may be obtained by evaporation of the solvent.

Natural fats may be purified from the albuminous substances which generally accompany them, when mechanically extracted, by gently warming with a little potash solution or sulphuric acid, by which the albuminoids are decomposed or dissolved. Care must be taken that the temperature employed be not too high, or the glycerine salts or fats will themselves be saponified or converted by the sulphuric acid into free fatty acid and sulpho-glyceric acid.

The decomposition of fats by water or steam at a high temperature, as well as their decomposition by ammonia into glycerine and acid amides, has already been considered.

The fats, when heated by themselves, undergo dry distillation, acroleïn being one of the constant products, depending on the presence of glycerine in the fat.

693. Only one formic ether of glycerine is known-glyceryl di

hydrate formate, or monoformin, C3H5.(OH)2(O.CHO). It is formed by heating glycerine with oxalic acid to 190°, and may be extracted from the cooled product of the reaction by ether, on the evaporation of which it remains as a colourless liquid, miscible with water and distilling unchanged in a vacuum. On heating to 200° it decomposes into CO2, water, and allyl alcohol (§ 663).

694. Acetic Acid Derivatives.-Glycerine heated with glacial acetic acid for some time to a temperature of 100° yields a mixed product, from which ether extracts

Monacetin, or glyceryl dihydrate acetate, formed according to the equation:

C2H(OH)3 + HO.C2H2O = OH2 + C2H¿(OH)2(O.C2H3O).

It is a colourless liquid, miscible with a small quantity of water, but is decomposed by a large quantity.

Diacetin, C3H5.(OH).(O.C2H3O)2, is formed by heating glycerine with a large excess of acetic acid to 200°. It may also be extracted from the cooled reaction product by ether. It is a liquid, and boils at 280°.

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Triacetin, glyceryl triacetate, CH,(O.C2H2O), obtained by long heating of diacetin with glacial acetic to about 250°, is a neutral oil of sp. gr. 1.174, boiling at 268°. It occurs naturally in small amount in the oil from the spindle tree (Evonymus europaeus).

695. In addition to the acetic ethers just mentioned, haloid acetates are also known.

Aceto-chlorhydrin, C3H5Cl(OH)(O.C2H3O), prepared by the action of acetylic chloride on glycerine:

C3H5(OH)3 + Cl.CO.CH, H2O + C3H5.Cl.(OH)C2O2Hз, as a liquid of boiling point 250°.

Aceto-dichlorhydrin, C3H5.Cl2.(O.C,H,O), is formed, together with dichlorhydrin, by passing hydrochloric acid gas into a mixture of glycerine and glacial acetic acid heated to 100°; also from dichlorhydrin and acetyl chloride. There appears to be two isomers of this body, the one prepared in the former manner having a boiling point 205, the latter, which is possibly CH,Cl.CH(O.C2H2O)CH2Cl, boiling at 1940-195°, and having sp. gr. 1.274 at 8°.

Both compounds give epichlorhydrin on saponification with potash :

C3H5.Cl2(O.C2H30) + 2KOH= KCl + KO.C2H2O + OH2
+ C3H,(:O).Cl.

Diaceto-chlorhydrin, C3H5Cl(OC2H3O)2, is best prepared by heating glycerine with acetic acid and acetyl chloride simultaneously. It boils about 245°.

Several corresponding bromine compounds are also known.

696. Analogous bodies to the acetins are produced by heating glycerine with the homologues of acetic acid. Many of these bodies. have been prepared.

Tributyrin, C3H5(O.CO.C3H7)3, occurs naturally in butter along with tricapronin, tricaprylin, tricaprinin, trilaurin, trimyrisin. tripalmitin, tristearin, and trioleïn.

Monopalmitin, C2H ̧(OH2)O.C1H310), is solid, and melts at 58°; dipalmitin, C3H(OH)(C16H31O2)2, at 59°; tripalmitin, CH(CH31O2)3, at 63°. The latter is found in nearly all animal and vegetable fats. It is most easily obtained from olive oil, which is a mixture of that substance with trioleïn, C3H5(O.C18H330)3, by cooling, and pressing the solid palmitin from the liquid oleïn, and recrystallising from a mixture of alcohol and ether. It forms pearly plates difficultly soluble in alcohol. It melts about 46°.

Mono-, di-, and tristearin can be artificially prepared from stearic acid and glycerine. The latter is a very general constituent of natural fats, animal fats or tallows being composed principally of that body with a little tripalmitin and trioleïn.

On treating tallow with cold ether, the two latter bodies may be extracted, most of the tristearin remaining behind. It may be dissolved and crystallised from warm ether, and got in pearly scales almost insoluble in cold alcohol and only very slightly so in warm ether. It melts at 63°. If it be not heated above 65° during the experiment it solidifies again at 61°, and then only melts again at 66. If it be heated, however, higher than 67°, it solidifies again at 51°, and then melts at 53°, but returns to the melting point, 63°, after some time.

Other ethers occurring in natural fats will be considered under the respective acids.

697. Lecithin. This name is applied to several bodies of very similar chemical and physical properties derived from brain substance, nerves, blood corpuscles, gall, &c., and also from some vegetable substances (maize, &c.), and which appear, indeed, as constant constituents of the cell substance of organised bodies. All these bodies, when decomposed by water, acids, or bases, give glycerinephosphoric acid, neurine, and fatty acids.

Every lecithin is a fat containing only two fatty acid radicals, the third hydroxyl group being replaced by ethylen-trimethyl ammonic hydrate (neurine) in combination with phosphoric acid.

The following general formula, in which X may be supposed to represent the acid radicals of palmitic, stearic, and oleic acids, exhibits the constitution of lecithin, and the equation, its decomposition by alkalies:

C2H,(OX)2.O.PO

-N(CH3)3

O.CH. CH2

+ 4KOH= 2KOX

+ C2H(OH)2.0.PO(OK)2 + HO.CH2.CH2.N.(CH3)3.OH.

Brain and nerve substance appear to contain the palmitic oleic lecithin, C42H82NPO:

O.C16H31.O
O.C1H33.O

C3H5

O.N.(CH3)3

O.PO

O.C2H,

The preparation of lecithin from brain substance is only accom

plished with great loss.

The brain substance must be freed as far as possible mechanically

Ꭰ Ꭰ

from blood vessels, cuticular substance, &c., rubbed up to a thin paste with water, and this repeatedly shaken out with ether, at a temperature of about 0°, until no more fat or cholesterine is taken up. The insoluble residue is then filtered from excess of water and pressed, after which it is heated with 80 % alcohol to between 40° and 45°. The warm alcoholic solution, after filtration and cooling, separates crude lecithin as a flocculent substance, which is again washed many times with ether to remove traces of fatty bodies, and finally crystallised from alcohol at a temperature of 45°. Lecithin may be obtained in a similar manner from amniotic liquid.

It can also be easily obtained from the latter substance by means of ether alcohol. After evaporating the ether and separating from the precipitated fats, an alcoholic solution of cadmic carbonate is added, which causes a precipitate of lecithin-cadmium chloride, which is suspended in water and treated with hydric sulphide. The lecithin hydrochloride thus set free is shaken out with ether, from which solution it is obtained by evaporation.

Lecithin crystallises from its saturated solution in alcohol in fine radially grouped needles, which dry up in vacuo to a white powder, which melts on gently heating. It is slightly soluble in cold alcohol and ether, much more freely on heating. It may also be crystallised from glacial acetic acid.

With bases and acids compounds are formed on the type of

698. Mercaptans.-Thio-hydrates of glyceryl are produced by the action of haloid glyceryl compounds on alcoholic solution of potassic sulph-hydrate according to the general equation:

C3H5.Cl(OH)з_ + aKSH = aKCl + C3H5(SH),(OH)3_a

3-a

in which a may have the values 1, 2, or 3. They have all the properties of the mercaptans proper, and exchange the hydrogen of their SH groups for mercury, copper, and similar metals.

Monosulph-hydrin, glyceryl thio-dioxyhydrate, C3H5.(SH).(OH)2, obtained by double decomposition between monochlorhydrin and potassic sulph-hydrate, is a colourless, thick liquid, of sp. gr. 1-295 at 14°, which gives off a very disagreeable odour when warmed. It is only slightly soluble in water and not at all in ether.

Disulph-hydrin, C3H5(SH),OH, obtained in a similar manner, only by using dichlorhydrin, has a sp. gr. = = 1.342, and is insoluble in water and ether.

Trisulph-hydrin, C3H5(SH)3, from trichlorhydrin. It is more

liquid than glycerine, of sp. gr. 1.391, and only soluble in strong alcohol.

Glyceryl trisulphocyanate, C3H5.(SCN)3, is the only sulphethereal salt of glycerine known. It may be prepared by the action of tribromhydrin on potassic sulphocyanate, and forms hard white needles melting at 126°.

699. Sulphonic Acids. The glyceryl mercaptans pass on oxidation with nitric acid into sulphonic acids.

The reaction takes place pretty directly with the monosulph-hydrin, glycerine monosulphonic acid, which yields soluble and crystallisable salts, being formed:

Glycerine disulphonic acid is easily obtained in the form of potassic salt by boiling dichlorhydrin with a concentrated solution of neutral potassic sulphite:

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C2H¿(OH)Cl2 + 2(K.SO2OK) = 2KCl + С2H5(OH).(SO2.OK)2. Trichlorhydrin yields in a similar manner the tribasic glyceryl trisulphonic acid:

C3H5Cl3 + 3K.SO2.OK = 3KCl + C3H5(SO2.OK)3.

Nitrogen Compounds of Glycerine.

700. Very few bodies of this class are known in a pure condition. Although the haloid glycerine compounds, like the haloid combinations of all other alcohol radicals, act upon aqueous ammonia, the products, especially in the case of the di- and tri-substitution, are so numerous and complicated that a perfect separation becomes almost impossible.

As far as is known, however, they are basic compounds corresponding to the alkylamines.

By heating dichlorhydrin with aqueous ammonia, the hydrochlorate of a glyceramine, or a basic substance which may either be glyceryl hydratamide, C,H,(OH)2NH2, or glyceryl oxide amide, C3H5(:O).NH2, is formed along with ammonic chloride.

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Homologues of Allyl and Glyceryl Derivatives.

Homologues of the glyceryl compounds with four carbon atoms are not known as yet; several penta- and hexacarbon homologues are, however, known.

701. Isoamyl Glycerine.-Isoamylene dibromide is converted by strong alcoholic potash solution into potassic bromide and bromisoamylene, CH,.Br. This latter is very probably a mixture of several isomeric bodies, and gives, on fractional distillation, a mobile oil, boiling between 100° and 110° and of not unpleasant odour.

Owing to its conversion, under the influence of hydrates, into a trihydric alcohol, the following formula appears most likely to express its constitution :