PRODUCTS, DERIVED FROM .MILK-SUGAR. 17 



to a dark red liquid : phenylgalactosazone is obtained in vellow 

 needles from ;ilcohoIic solutions, which, melt at 188'" to 19]^ C. 

 with decomposition. They are converted into osones bv treat- 

 ment with strong cold hydrochloric acid. 



Products derived from Milk-Sugar.— The most important of 

 these products is formed by the action of certain micro-organisms 

 on milk-sugar during the so-called lactic fermentation. By their 

 action the milk-sugar is split up into lactic or oxypropionic acid 

 almost quantitatively, a certain portion, however, being con- 

 verted into other products, of which carbon dioxide is the most 

 important. The micro-organisms which produce lactic acid arc 

 acted on inimically by acids, so that not much more than 1 per 

 cent, of lactic acid is usually formed, unless the solution is kept 

 neutralised bv iliiilk or other means. 

 H 



Its formula is CH,— C— (JOOH, and it contains an asvmmetric 



I 

 OH 



carbon atom ; it is not, however, optically actiN-e, though tlie 



isomeric sarcolactic acid possesses this property'. It appears tn 



be a racemic compound; but both the dcxtro- and lajvo-acids 



are produced by certain micro-organisms. It has a remarkable 



tendency to form compounds which contain less watei-. 



On evaporating a((ue<ms solutions of lactic acid, dehvdrol.ietic 



acid is formed, C',;H||,0-,, which, by further evaporation (es|)eeialh' 



at a high tempciature), gives lactide, t'^H^O^. 



La<-tie acid acts as a monobasic acid ; while dehydiolaetic 



acid behaves as a monobasic acid, monohydric alcohol and 



an ethereal salt at the same time : lactide is a. neutral 



substance. 



Sarcolactic acid gives the same lactide, which, on boiling with 



water, is converted into the inactive modification. 



The so-called syrupy lactic acid is a mixture of lactic and 



dehydiolaetic acids with probably a little lactide. Wislicenus 



has shown that by direct titration with alkali lactic, and dehydro 



lactic acids are estimated, while bv further boding with excess 



of alkali one molecule of lactic acid is produced for each molecule 



of dehydrolactic acid, and two for each molecule of lactide. 



Dehydrolactic acid has not been obtained pure, but appears to 



be amorphous and nearly insoluble in water. 



Lactide can be prepared by subliming syrupy lactic acid at 



I'lU-" in a current of dry air. It is insoluble in water, but can 



be ( rvstallised from alcohol m colourless rhombic plates melting 



atl:i4-5'C. It boils at --'.mC. 



S\ rupv lactic acid is said to have a specific gra^^ty of r248.'i. 



La( tie acid is not appreciably volatile in dilute solution, but 



