106 METHODS OF ANALYSIS [Chap. 



DEXTROSE. 



50 Approximate Volumetric Method for Rapid Work. — Tentative. 

 Proceed as directed under 21 . Standardize the reagent against pure dextrose. 



51 Soxhlet Method.— Tentative. 



Proceed as directed under 23. Under these conditions 100 cc. of the reagent 



require 0.475 gram of anhydrous dextrose for complete reduction and the formula 



100 X 0.475 . r ^ . 



becomes ; = per cent of dextrose. 



VW 



52 General Gravimetric Method. — Tentative. 



Proceed as directed under 25 and obtain, from 27, the weight of dextrose equiv- 

 alent to the weight of copper reduced. 



Allihn Gravimetric Method. — Tentative. 



53 REAGENT. 



Allihn' s Modification of Fehling's Solution. — Prepare by mixing, immediately 

 before use, equal volumes of (a) and (b). 



(a) Copper sulphate solution. — Dissolve 34.639 grams of copper sulphate 

 (CuS045H,0) in water and dilute to 500 cc. 



(b) Alkaline tartrate soZuh'on.— Dissolve 173 grams of Rochelle salts and 125 

 grams of potassium hydroxid in water and dilute to 500 cc. 



54 DETERMINATION. 



Place 30 cc. of the copper sulphate solution, 30 cc. of the alkaline tartrate solu- 

 tion, and 60 cc. of water in a beaker and heat to boiling. Add 25 cc. of the solution 

 of the material to be examined, prepared so as not to contain more than 0.25 gram 

 of dextrose, and boil for exactly 2 minutes, keeping the beaker covered. Filter 

 immediately through asbestos, and obtain the weight of copper by one of the methods 

 given under 26, 29-34 inclusive. The corresponding weight of dextrose is found 

 in 55. 



