294 CONSIDERATION OF CARBON COMPOUNDS. 



Bismuth citrate, BiC 6 H 5 O 7 , is obtained by boiling a solution of 

 citric acid with bismuth nitrate, when the latter is gradually 

 converted into citrate whilst nitric acid is set free ; the insoluble 

 bismuth citrate is collected, washed and dried ; it forms a white, 

 amorphous powder, which is insoluble in water, but soluble in 

 water of ammonia. 



Bismuth ammonium citrate is a scale compound obtained by 

 dissolving bismuth citrate in w^ater of ammonia and evaporating 

 the solution at a low temperature. 



Ferric citrate, Ferri citras, Fe 2 2(C 6 H 5 O 7 )6H 2 O. Obtained in 

 transparent, red scales, by dissolving ferric hydrate in citric 

 acid and evaporating the solution as mentioned heretofore. By 

 mixing solution of ferric citrate with either water of ammonia, 

 or quinine, or strychnine, evaporating to the consistence of 

 syrup and drying on glass plates, the following three scale com- 

 pounds are obtained respectively : Citrate of iron and ammonia, 

 citrate of iron and quinine, citrate of iron and strychnine. 



Lactic acid, Acidum lacticum, HC 3 H 5 3 = 90. This acid is the 

 second member of a group of monobasic, diatomic acids which 

 have the general composition C n H 2n O 3 , and which contain two 

 hydroxyl groups, the hydrogen of one being capable of replace- 

 ment by metals, the other by alcohols. The first member of 

 this series is glycollic acid, HC 2 H 3 O 3 , a white, deliquescent, crys- 

 talline substance. 



Lactic acid occurs in many plant-juices, it is formed from 

 sugar by a peculiar fermentation known as " lactic fermentation," 

 which causes the presence of this acid in sour milk and in many 

 sour, fermented substances, as in enselage, sauer-kraut, etc. 

 The formation of lactic acid from sugar may be expressed by 

 the equation : 



C 6 H 12 6 : : 2(HC 3 H 5 o 3 )- 



Sugar. Lactic acid. 



For practical purposes lactic acid is made by mixing a solution 

 of sugar with milk, putrid cheese, and chalk, and digesting this 

 mixture for several weeks at a temperature of about 30. The 

 cheese acts as a ferment, and the chalk neutralizes the acid 

 generated during the fermentation. The calcium lactate thus 

 obtained is purified by crystallization and decomposed by oxalic 

 acid, which forms insoluble calcium oxalate. 



