LACTIC ACID. 85 



lactic acid stands to metacetonic acid ; and, in point of fact, 

 Cahours,* and subsequently Strecker,f arrived at the discovery of 

 some such acids by a perfectly different train of ideas from that 

 which we have pursued. The latter, in employing Piria's method 

 of decomposing the amide compounds, (given in p. 36,) with the 

 view of ascertaining whether certain nitrogenous animal substances 

 were amides, found two such acids constituted according to the 

 above general formula. In treating glycine with nitrous acid, he 

 discovered an acid=C 4 H 3 O 5 .HO, corresponding to acetic acid, 

 and on treating leucine in a similar manner, he obtained an acid 

 = C 12 H 11 O 5 .HO, analogous to caproic acid. 



Acetic acid .... C 4 H 3 O 3 . HO corresponds to glycic acid C 4 H 3 O 5 . HO 



Metacetonic acid .... C 6 H 5 O 3 . HO lactic acid C 6 H 5 O 5 . HO 



Caproic acid ... C 12 H U O 3 . HO leucic acid C 12 H U O 5 . HO 



In the decomposition of hippuric acid, according to the same 

 method, Strecker obtained a new acid, whose composition is not 

 in accordance with the above formula, but is very similar to that of 

 lactic acid: it is represented by the formula C 18 H 7 O 7 . HO; hence 

 it is analogous in its constitution to the neutral carbo-hydrates of 

 the vegetable kingdom (starch, sugar, woody fibre) ; that is to say, 

 in addition to carbon it contains hydrogen and oxygen in the 

 exact proportions to form water. Here, too, we should place the 

 cholestericacid=C 8 H 4 O 4 .HO, discovered by Redtenbacher, which 

 also presents much similarity in its characters with the above- 

 named acids of the carbo-hydrates. 



There is little to be said regarding the general properties of the 

 acids of this group, as in truth, lactic acid is the only one of them 

 with whose characteristics we are accurately acquainted. It appears, 

 however, from Strecker's communications, that all these acids, 

 when deprived as much as possible of water, occur as oily, non- 

 crystallisable fluids, redden litmus strongly, undergo decomposition 

 when heated, and form soluble and in part crystallisable compounds 

 with bases. 



LACTIC ACID. C 6 H 5 O 5 .HO. 



Chemical Relations. 



Properties. In its most concentrated state lactic acid is a colour- 

 less, inodorous, thick, syrupy fluid, which cannot be solidified by 

 the most intense cold; its specific gravity = 1*215; it dissolves 

 * Compt. rend. T. 27, p. 267. 

 t Ann. d. Ch. u. Pharm. Bd. 68, S. 52-55. 



