634 PHYSIOLOGICAL CHEMISTRY 



Folin-Wu Blood Sugar Reagents. 1 (a) Standard Sugar Solutions. 

 Three standard sugar solutions should be on hand: (i) a stock solution, 



1 per cent glucose or invert sugar, preserved with xylene or toluene; 

 (2) a solution containing i mg. of sugar per 10 c.c. (5 c.c. of the stock 

 solution diluted to 500 c.c.); (3) a solution containing 2 mg. of sugar per 

 10 c.c. (5 c.c. of the stock solution diluted to 250 c.c.). The invert 

 sugar solution has the advantage that it can be easily prepared from 

 cane sugar, which is pure. 



When good quality glucose is available, it is, of course, the one to use. 

 The diluted solutions should be preserved with a little added toluene 

 or xylene; it is probably better not to depend on such diluted solutions 

 to keep for more than a month, but the stock solution should keep 

 indefinitely. 



(b) Alkaline Copper Solution. Dissolve 40 gm. of pure anhydrous 

 sodium carbonate in about 400 c.c. of water and transfer to a liter 

 flask. Add 7.5 gm. of tartaric acid, and when the latter has dissolved 

 add 4.5 gm. of crystallized copper sulfate. Mix and make up to a 

 volume of i liter. If the chemicals used are not pure a sediment of 

 cuprous oxide may form in the course of i or 2 weeks. If this should 

 happen, remove the clear supernatant reagent with a siphon, or filter 

 through a good quality filter paper. The reagent seems to keep 

 indefinitely. To test for the absence of cuprous copper in the solution, 

 transfer 2 c.c. to a test tube and add 2 c.c. of the molybdate phosphate 

 solution; the deep blue color of the copper should almost completely 

 vanish. In order to forestall improper use of this reagent attention 

 should be called to the fact that it contains extremely little alkali, 



2 c.c. by titration (using the fading of the blue copper tartrate color 

 as indicator), requiring only about 1.4 c.c. of normal acid. 



(c) Molybdate-tungstate Solution. Transfer to a liter beaker 35 gm. 

 of molybdic acid and 5 gm. of sodium tungstate. Add 200 c.c. of 

 10 per cent sodium hydroxide and 200 c.c. of water. Boil vigorously 

 for 20 to 40 minutes so as to remove nearly the whole of the ammonia 

 present in the molybdic acid. (The molybdic acid which may be 

 obtained from the Primos Company, Primos, Pa., contains consider- 

 able ammonia.) Cool, dilute to about 350 c.c., and add 125 c.c. of 

 concentrated (85 per cent) phosphoric acid. Dilute to 500 c.c. 



Formalin Solution (Neutral). 2 To 50 c.c. of commercial formalde- 

 hyde solution. (30-40 per cent) add i c.c. of phenolphthalein solution 

 and then standard alkali solution until the mixture assumes a faint 

 red color. The solution should be freshly prepared for each set of 

 determinations. 



1 Folin-Wu blood sugar method, p. 283. 2 Formol titration procedure, p. 521. 



