38 PHYSIOLOGICAL CHEMISTRY. 



oxide dissolves in ammonia without color to prepare a quan- 

 titative solution with which this difficulty may be largely over- 

 come. Pavy was the first to employ such a reagent prac- 

 tically and his solution was made by diluting the ordinary 

 Fehling's solution with ammonia in certain proportion. His 

 suggestion has received several modifications. In all of these 

 the weak sugar solution is added to the boiling ammoniacal 

 copper solution until the color of the latter is just discharged, 

 at which point the reduction of the copper hydroxide by the 

 sugar is complete. In place of using the Fehling's solution 

 it is well to make the Loewe solution with glycerol the basis 

 of the dilution. A solution of this kind may be made by the 

 formula below, in which the proportions have been found by 

 the present writer to give the best result in practical work. 

 One cubic centimeter of the solution oxidizes one milligram 

 of glucose in 0.2 per cent solution. 



It is made with the following amounts per liter : 



Copper sulphate, cryst 8.166 gm. 



Sodium hydroxide (100 per cent) 15.000 " 



Glycerol 25.000 cc. 



Ammonia water, 0.9 sp. gr 350.000 " 



Water to make 1,000.000 " 



Ex. Of this solution, measure 50 cc. into a flask and dilute with water 

 to loo cc. To prevent too rapid an escape of ammonia and avoid reoxida- 

 tion to some extent, add to the mixture, while warming, enough pure white 

 solid paraffin to make a layer 3 or 4 millimeters in thickness when melted. 

 The burette tip for discharging the sugar solution is made long enough to 

 pass down the neck of the flask and below this paraffin. By boiling gently 

 and adding the weak saccharine liquid slowly, very close and constant re- 

 sults may be obtained. At the end of the titration the paraffin is solidified 

 by inclining the flask and immersing it in cold water, or by flowing cold 

 water over it. The reduced liquid is then poured out and the cake of 

 paraffin is thoroughly washed for the next test. A flask so prepared may 

 be used for a hundred titrations. To prevent bumping and facilitate easy 

 and uniform boiling, it is well to add a few very small fragments of pumice- 

 stone. 



A solution made as above is not too strong in copper for accurate work, 

 but the volume of ammonia necessary to hold a much larger amount of the 

 reduced oxide in solution would render the process very inconvenient. 

 Some practice is necessary to show just how fast the saccharine solution 



