THE URINE. 199 



The Determination. 



Dilute the sugar solution or the urine so that the fluid 

 contains about 0.5 per cent, of sugar or somewhat; more, and 

 put this solution into a burette. 1 Then measure off accu- 

 rately with a pipette 10 cc. of the Fehling's solution into a 

 moderately deep porcelain dish or into a flask, add about 40 

 cc. of water, heat to boiling, and then let the sugar solution, 

 run in. Red cuprous oxide or yellow cuprous hydroxide 

 very soon precipitates. On further addition of the sugar 

 solution the precipitate of the cuprous oxide increases, while 

 the blue color of the solution decreases. It is now necessary 

 to recognize the point when the blue color of the fluid disap- 

 pears, i.e., when all the copper oxide has been reduced and 

 yet no excess of sugar is present. When it is thought that 

 this point is nearly reached, filter a small quantity of the 

 fluid, removed by means of a pipette, through a small filter 

 of very close filter-paper the filtrate must contain no sus- 

 pended cuprous oxide, which very readily goes through the 

 filter acidify with hydrochloric acid and make alkaline 

 with ammonia: the fluid must not turn blue. If it does, 

 then add 0.5 cc. more of the sugar solution, heat and test 

 again for copper, etc. Of course this first titration is always 

 only an approximation. If the first test shows that the 

 solution is free from copper, it is possible that too much 

 sugar solution has been added, and the entire determination 

 must then be repeated and the sugar solution must be added 

 more carefully. The strength of the dilute sugar solution 

 in per cent, is equal to 5 divided by the number of cubic cen- 

 timeters used to complete the reaction. 



1 The specific gravity is to be used to determine the amount of the 

 dilution ; of course it is not always possible at the first attempt to make 

 the correct dilution- 



