by treatment with baric carbonate, the sulphuric acid is removed and free creatinine obtained by evaporation of the filtrate.

In

Creatinine does not occur in flesh, but does in urine, a fully grown man excreting about 6-13 gram creatinine in 24 hours. order to prepare it from urine, this is concentrated to about of its bulk, then made faintly alkaline by means of milk of lime, and calcic chloride added so long as a precipitate-consisting mainly of calcic phosphate-falls down. The filtrate is evaporated to a syrup, the sodic chloride which crystallises out removed, and the mother liquor mixed with a syrupy solution of zincic chloride. The difficultly soluble creatinine zincic chloride soon separates, which is purified by crystallisation and decomposed by boiling with water and plumbic oxide. Basic plumbic chloride and zincic oxide precipitate whilst the solution contains creatinine and creatine-formed from the former by union with water-which, after evaporation to dryness, are separated by means of alcohol.

Creatinine crystallises in long colourless monoclinic prisms, which dissolve readily in water and alcohol, and have a strongly alkaline reaction. It unites with acids to form salts of neutral reaction, which contain an equivalent of acid to each molecule of creatinine. hydrochloride yields with platinic chloride a double salt :

(C4H,N2O,HCl)2,PtC14,

pretty soluble in water, difficultly in alcohol.

The

A very characteristic creatinine salt is creatinine zincic chloride, (C,H,N30)2ZnCl2. In this hydrogen has been replaced by zinc somewhat in the fashion of the formula:

It crystallises in groups of fine needles, difficultly soluble in water, insoluble in alcohol.

With hydrochloric acid it yields a further very readily soluble crystalline salt, (C1H,N2O.HCÎ)2ZnCl2.

By long contact with water creatinine is converted into creatine, especially in the presence of basic hydrates, so that it can only be obtained in part unaltered from its salts.

By boiling with solution of baric hydrate, ammonia is first evolved, methyl hydantoin being formed (§ 725):

CH2.N-CH3

C-NH + H2O = NH3

CO.NH

CH2.N-CH3
CO

CO. NH

which soon decomposes into methyl glycocine, baric carbonate, and ammonia. With mercuric oxide or plumbic dioxide and sulphuric acid it yields the same products as creatine.

On heating creatinine for a long time at 100° with alcohol and ethylic iodide, ethyl creatinine hydriodide, C1H6(C2H5)N3O,HI, is formed, from which argentic oxide liberates ethyl creatine:

C1Hg(C2H5)N3O2,

crystallising in needles grouped in bundles, of strongly alkaline reaction.

Lactic Acids, C3H603.

729. The isomeric lactic acids occupy the second place in the series of hydroxy acids. So far as these are hydroxy-propionic acids there can only be two isomers, namely:

CH3

CH.OH

CO.OH

a-Hydroxy-propionic acid,

B-Hydroxy-propionic acid, or ethylidene hydrate carbonic acid. or ethylene hydrate carbonic acid There are, however, four isomeric monobasic acids known of this formula, C3H6O3, of which two, ordinary lactic and paralactic acids, have the structural formula of a-hydroxy-propionic acid; ethylene lactic acid is ß-hydroxy-propionic acid, whilst in the case of the fourth, hydracrylic acid, the order of arrangement of the atoms has not yet been determined with certainty.

1. Ordinary or Fermentation Lactic Acid.

Optically Inactive Ethylidene Lactic Acid, CH3.CH(OH).CO.OH.

730. Ordinary lactic acid occurs in small quantity in the animal organism, especially in the gastric juice, and is formed under certain circumstances in the fermentation of some sugars. In the latter way it is formed in sour milk, in sauerkraut, &c.

It is prepared from propionic acid by means of the halogen substitution products. On heating dry propionic acid with a molecule of bromine in closed tubes to 130°, the liquid soon decolourises, and then contains, together with much hydrobromic acid, principally a-brompropionic acid:

+

CH..CH,CO.OH + Brg =CH,.CHBr.COOH + HBr. The salts of this latter, on boiling with water, alkalies, or argentic oxides, are converted into a-oxypropionic acid, just as the haloid acetic acids are converted into glycollic acid:

CH..CHBr.C0.0Ag + H,O = AgBr +CH,.CH(OH)COOH. Its structure is shown by its synthetical preparation from ethylidene compounds, especially from ethylidene oxide or acetic aldehyde ($ 390). On mixing the latter with hydrocyanic acid, they unite together to form ethylidene hydrate cyanide, which on treatment with strong hydrochloric acid is converted into lactic acid even at the ordinary temperature. Aldehyde ammonia is converted by prussic acid into ethylidene-amide cyanide, this by aqueous hydrochloric acid into alanine, and the latter is converted into lactic acid by nitrous acid (formule and equations, § 705, 5, a and b).

Other methods of formation of ordinary lactic acid, as from glyceric acid and pyrotartaric acid, will be mentioned later at their respective places.

Lactic acid is most readily prepared by a peculiar fermentation of

sugar. For this purpose 3 kilograms of cane sugar and 15 grams of tartaric acid are dissolved in 17 litres of boiling water. Thereby the cane sugar, C12H22O11, is split up under the influence of the tartaric acid, and with combination with a molecule of water, into 2C6H12O6 (grape sugar and fruit sugar). There is then added, to sow the necessary ferment, 100 grams of old cheese or of putrid flesh, mixed with 4 litres of sour milk, and 14 kilogram of zinc white or zinc carbonate, and the whole allowed to stand for a long time, best at a temperature of 40°-45°. After eight to ten days the change :

C&H12062C3H6O3,

is finished, and at the bottom of the vessel, in place of the basic zinc salt, crusts of zincic lactate are found, which are purified by recrystallisation from hot water and then decomposed in boiling solution by sulphuretted hydrogen. The liquid, freed from zincic sulphide, is then evaporated to a thin syrup on the water bath, and separated from any undecomposed zinc salt or mannite by solution in ether. The separated ethereal solution is distilled from the water bath, and finally warmed for some time in an open vessel.

In this way there is obtained a colourless, strongly acid syrup, from which, however, pure lactic acid of the formula C3H6O3 cannot be obtained. If much water is present there is no doubt a body of the formula:

CH3.CH(OH).C(OH)3,

which, on further evaporation, decomposes into water and lactic acid. As soon as the latter has attained certain proportions, single lactic acid molecules etherify, and both ethereal anhydrides are formed in greater proportion the further the concentration is carried. The syrupy preparation termed lactic acid is therefore a mixture of CH.CH(OH).C(OH)3, CH3.CH(OH)CO.OH, C6H1005, and often also of CHO. On further drying in vacuo over sulphuric acid it becomes quite stiff, and then consists essentially of the two ethereal anhydrides.

By distillation of an aqueous solution much unaltered lactic acid passes over in the aqueous vapour; by heating the syrupy preparation, on the other hand, the formation of the ethereal anhydrides is increased. If the temperature is raised slowly, much of the second anhydride (lactide) volatilises, whilst by quick heating to higher temperatures the greater part is decomposed into aldehyde, carbonic oxide, and

water:

CH,.CH(OH).CO.OH = CH.CHO + CO + H,O.

By heating with dilute sulphuric acid to 130° it is decomposed into aldehyde and formic acid :

CH,.CH(OH).CO.OH=CH,.CHO + HCO.OH. Oxidising agents, e.g. chromic acid, oxidise it to acetic acid, carbonic anhydride, and water:

CH3.CH(OH).CO.OH+20= CH3.CO.OH + CO2 + OH2.

By heating with concentrated hydriodic acid, lactic acid is reduced to propionic acid (a-iodo-propionic acid being first formed):

CH3.CH(OH).CO.OH + 2HI = H2O + I2 + CH3.CH2.CO.OH.

Putrefactive ferments convert a solution of lactic acid or its salts into normal butyric acid.

731. Lactates. In the replacement of hydroxylic hydrogen by metals, lactic acid acts as a monobasic acid, which is also a monhydric alcohol. Carbonates only replace the acid hydrogen, as do also most of the basic hydrates; the alkaline salts, on heating with alkali metal, have their alcohol-hydroxylic hydrogen atom replaced also.

The neutral alkali salts of lactic acid are deliquescent, also soluble in alcohol, and yield on evaporation of their solutions solid amorphous masses, which melt on gentle heating.

Sodic lactate, CH3.CH(OH).CO.ONa, after long drying in vacuo forms a solid mass, consisting of fine hair-like crystals. When fused it dissolves sodium with evolution of hydrogen, and is converted partially into the compound CH3.CH(ONa)CO.ONa, which, like the sodic alkylates, is decomposed by water into free alkali and neutral salt.

Calcic lactate, [CH3.CH(OH).CO.0],Ca,5 H2O, crystallises in aggregates of small thin needles, soluble in 9 parts of cold water and also in alcohol. If the aqueous solution is mixed with two molecules of lactic acid, an acid salt, C6H10CaO6,2C3H6O3,2H2O2, crystallises on evaporation. This may be expressed by a formula similar to that given for the acid acetates:

The double salt, C6H10CaO6,2C3H,KO3, obtained by evaporation of equivalent quantities of the calcic and potassic salts, has a similar constitution.

Zincic lactate, C6H10ZnO6,3H2O, is the most characteristic salt of lactic acid. It crystallises in small colourless monoclinic prisms, generally united to crusts. It requires for solution about sixty parts of cold, and only six parts of boiling, water. It is nearly insoluble in alcohol. Ferrous lactate, [CH.CH(OH)CO.O],Fe,3H2O, possesses similar properties.

732. Ethereal Anhydrides of Lactic Acid.-As already mentioned, the ethereal anhydrides are obtained from lactic acid in a dry atmosphere even at ordinary temperatures, as also on heating, especially at temperatures above 100°.

First ethereal anhydride, lactyl lactate :

is a yellow amorphous mass, scarcely soluble in water, but readily in alcohol and ether; on boiling with water or alkalies it is reconverted into lactic acid.

The dehydration easily proceeds further, yielding the second ethereal anhydride, or lactide:

This is obtained in larger quantity when lactic acid or the first ethereal anhydride is heated for a long time at 150° in a tubulated retort through which a slow stream of air is drawn. The neck of the retort is soon coated with a crystalline coating of lactide, which is from time to time removed by fusion, washed with cold alcohol, and finally crystallised from boiling alcohol.

Lactide forms colourless rhombic tables, melting at 124·5° and distilling at 255. The vapour density is 4.81. It is insoluble in water, but is slowly decomposed thereby into the first ethereal anhydride, and finally into lactic acid. It is much more readily saponified by

alkalies.

733. Ethylic lactate, CH3.CH(OH).CO.O.C2H,, is formed by heating lactic acid, or still better a mixture of the anhydrides, with alcohol to 170°. Ethylic lactate is separated from the products by fractional distillation as a colourless liquid of peculiar odour, boiling at 156°, which mixes with water, but is soon decomposed by this into alcohol and acid.

Sodium dissolves in pure ethylic lactate with evolution of hydrogen, as in an alcohol, yielding the so-called ethylic sodio-lactate :

CH3.CH (ONa)CO.O.C2H ̧,

a solid mass decomposed by water into free alkali and ethylic lactate which then further react on each other as above.

734. On mixing ethylic lactate with an acid haloid, e.g. with acetyl chloride, the alcoholic group of the former reacts energetically with the halogen compound (§ 608), ethylic aceto-lactate being formed:

CH.CH.OH

со.о.с.н,

+ Cl.C2H2O HC1 +

= =

CH,CH.O.C,H,O

со.о.с.н,

It boils at 177°, has an agreeable odour, sp. gr. 1·0458 at 17°, and is insoluble in water. If heated with a little water to 150°, and then submitted to distillation, ethylic alcohol passes over, whilst a strongly acid syrup of aceto-lactic acid, CH3.CH(O.C2H30)CO.OH, remains behind. This yields in general gummy salts, completely decomposed on long heating, or more readily by boiling with alkalies, into lactic and acetic acids or the respective salts.

735. Nitro-lactic acid, or lactic acid nitrate, is prepared by introducing syrupy lactic acid into a mixture of concentrated sulphuric and nitric acids:

CH3.CH.OH

COOH + HO.NO2 + H2SO, =

CH3.CH.O.NO,

CO.OH

+ H1SO

and is extracted from the reaction mass after dilution with water by shaking with ether. It forms a thick, strongly acid liquid but little soluble in water, readily soluble in alcohol and ether, and decomposes on standing.

736. Halogen Compounds of Lactyl.-On saturating lactic acid with hydrochloric or hydrobromic acid and heating in sealed glass tubes, a-halogen propionic acids are formed: