LACTOSE. 19 



When these solutions have cooled mix them, add 450 cubic 

 centimeters of concentrated ammonia (sp. gr. 0.9) and dilute to 

 1000 cubic centimeters. 



For the titration use 35 cubic centimeters copper solution 

 diluted with about twice its volume of water. Heat this to boil- 

 ing, then drop in slowly from a burette the urine or glucose solu- 

 tion until the blue has been destroyed. Three to five seconds 

 should elapse between the drops. When this has occurred 0.02 

 gramme of glucose has been added. The solution should then be 

 colorless. If it is yellow an excess of sugar has been added. From 

 the volume of solution used calculate the per cent, of glucose by 

 weight. 



LACTOSE (MILK-SUGAR: C 12 H 22 1;l + H 2 0). 



Lactose is found in the milk of all mammals and occa- 

 sionally during pregnancy in the urine. It can be obtained 

 from the milk by crystallization after the removal of the 

 nitrogenous constituents. 



It is a crystalline substance, soluble in water, with a 

 faint sweetish taste. With pure yeast it does not ferment. 

 By the action of certain other ferments, however, it under- 

 goes alcoholic fermentation, with the production at the 

 same time of lactic acid, forming the drinks known as 

 <r koumiss," when made from mares' milk, and "kephyr" 

 when from cows' milk. The ordinary souring of milk is 

 due to the formation of lactic acid from the lactose by 

 micro-organisms. 



Milk-sugar gives with many reagents the same results 

 as glucose. It can be distinguished from glucose by its not 

 fermenting with yeast and by its having a less strong power 

 of reduction, it is unable to reduce cupric compounds to 

 cuprous in acetic acid solutions (Barfoed's test). 



34. PREPARATION OF MILK-SUGAR. Dilute 200 

 cubic centimeters of milk with 800 cubic centimeters of 

 water, and add very cautiously not more than 0.1 per cent. 



