LACTIC ACID (from lacte, milk) is the substance that gives the well known acidity to sour milk. It is produced from the milk-sugar by the fermentive action of the casein or cheese portion. This acid is also met with in many other processes where starches or sugars other than milk-sugar are undergoing fermentation. It occurs in the fluids of the muscular tissue. When required in quantity lactic acid is most conveniently prepared by adding one part of common cheese to a solution of eight parts of milk-sugar in about fifty of water, stirring in three parts of powdered chalk and setting the whole aside for two or three weeks- in a warm place (80° Fahr.). Tho mixture slowly becomes filled with crystals of lactate of lime, these are separated by straining, purified by re-crystallisation from water, decomposed with about one-third of their weight of sulphuric acid, and the liquor, freed from the sulphate of lime by filtration, is decolorised by treatment with animal charcoal, and concentrated by evaporation.
Lactic acid is uncrystallisable. When pure it has the consistence of strong syrup, is transparent, colourless, inodorous, of intensely acid taste, and has a specific gravity of P21. Exposed to the air it absorbs water, iu which it is soluble in all proportions. It is also very soluble in alcohol and ether. An exceedingly minute quantity of it at once causes the coagulation of boiling milk. Nitric acid converts it into oxalic acid. By careful application of heat to lactic acid, contained in vessels from which air is excluded, it may be distilled ; but at a tem perature of 500° Fahr. is converted into carbonic acid, aldehyd, citraconic acid, lactide and lactone By the continued action of a heat of about 266° Fahr. lactic acid is gradually converted into lactic anhydride a fusible, bitter substance of yellow colour, insoluble in water, but gradually re-converted by prolonged contact with that liquid into lactic acid. • Lactose is a pungent volatile liquid. Boiling point 198° Fahr.
Lactide obtained in the manner just described, crystal lises from alcohol in clear white rhomboidal tables. It may be sublimed without undergoing decomposition. Water gradually con verts it into lactic acid, and ammonia forms with it lactamide.
lAebasside N,0,) Is also obtained by the action of lactic acid ass ammonia. It 14 interesting as being identical in composition with bodies, akrune, sartosine, and urethane (carbaunate of the oxide of ethyl). They lava all of them, however, very distinct this substance differs from the others in yielding lactic MA.1 ammonia when acted on by adds and bases; hence its name. It is very soluble in alcohol and water, and crystallises in plates or prisms.
Lectinde add, in combination with ammonia, results from the action of the dry gas upon lactic anhydride. The salt contains Metallic derirataceo of lactio acid. One or two equivalents of the hydrogen In lactic acid may be replaced by one or two equivalents of metal forming respectively acid and neutral salts ; the latter are more stably than the former. The salts of the alkalies do not crystallise; those of tetra and lime with difficulty ; that of sane (neutral) in four-aided preen*.
The true coastiortita of lactic add is not yet clearly determined. Wurta has recently succeeded in obtaining a lactic ether which may be said to contain four equivalents of ethyl in the place of an equal number of hydrogen in lactic, acid. Wurtz, however, eon/riders that lactic acid is the alcohol of a biatoinie radical lady' and fa thus formulated : C.fl.o." Rif j In addition to lactic ether just mentioned, Wurtz has obtained lacto butyric ether by the re-action of ehlarolactic ether (C,II,O,", CI, on butyrate of potash. The following are his for these two ethers :— C.ft,O," C.II,O," ;It,. J • C,I1,0" Lactic ether. Lsetobutyrie ether.
Corresponding metallic derivatives are said to have been produced hut not without difficulty in the case of the second atom of hydrogen in the lactic acid as represented by Wurtz. Those containing one atom only of hydrogen replaced correspond to the salts already men tioned under the name of neutral salts of lactic acid ; while the acid salts described at the same place would, under \Vurtz'e view, some what resemble quadrosalates, and be derived from a double equivalent of his lactic acid by substitution of an atom of metal for one of hydrogen.