A liquor composed of 75 per cent. of absolute lactic acid and 25 per cent. of water.

Characters. - A nearly colourless syrupy liquid, odourless, having a very acid taste, and an acid reaction. Sp. gr., 1.212. It is freely miscible with water, alcohol and ether, but nearly insoluble in chloroform. It is not vaporised by a heat below 160° C. (320° F.); at higher temperatures it emits inflammable vapours, then chars, and is finally entirely volatilised, or leaves but a trace of residue.

Preparation. - By adding chalk to sour milk and decomposing the lactate of calcium with sulphuric acid (vide p. 566).

Impurities. - Hydrochloric acid, sulphuric acid, sarcolactic acid, lead, iron, sugars, glycerin, organic impurities.

Tests. - When diluted with water, lactic acid should afford no precipitate with test solutions of nitrate of silver, chloride of barium, sulphate of copper, nor with sulphide of ammonium after the addition of excess of water of ammonia. It should not reduce warm test-solution of potassio-cupric tartrate. When mixed and heated with excess of hydrated zinc oxide and extracted with absolute alcohol, the latter should not leave a sweet residue on evaporation. Cold concentrated sulphuric acid shaken with an equal volume of lactic acid should assume at most only a pale yellow colour.

Dose. - 1 to 3 fl. dr. per diem, diluted or sweetened, like lemonade.

When used as a caustic it may either be applied on lint covered with gutta percha or as a paste of silica saturated with the acid. After being left on for 12 hours it should be washed off, and the application renewed as necessary.

Preparation.

B.P.

Dose.

Acidum Lacticum Dilutum (acid 3, water up to 20)......

1/2-2 fl. dr.

Action. - It has been employed in a solution of 1 part to 5, to dissolve the false membrane in croup and diphtheria. In cases of dyspepsia it is used to aid digestion in somewhat the same way as hydrochloric acid, and it has been given also to lessen the alkalinity of the urine and prevent phosphatic deposits. In diabetes it has been employed with considerable success along with an exclusively meat diet in doses of 1/2 oz. in 1 pint of water daily, though it is said to have given rise to rheumatism in a diabetic patient. Buttermilk has been recommended in place of it, but the difficulty of obtaining this in towns is very great.