MICROCHEMICAL METHODS FOR BLOOD ANALYSIS 307 



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

 c.c. of 10% sodium hydroxide and 200 c.c. of water. Boil vig- 

 orously for 20 to 40 minutes so as to remove nearly the whole 

 of the ammonia present in the molybdic acid. Cool, dilute to 

 about 350 c.c. and add 125 c.c. of concentrated (85%) phos- 

 phoric acid. Dilute to 500 c.c. 



It will be seen that the preparation of this reagent is much 

 simpler than the preparation of the phenol reagent. The solu- 

 tion has none of the yellow color of the phenol reagent, yet 

 gives an intense blue color with cuprous oxide. Since the reac- 

 tion takes place in acid solution the blue color of the alkaline 

 copper tartrate is also eliminated. The sodium tungstate con- 

 tained in this reagent is added because there is sodium tung- 

 state in our blood nitrates, and tungstates modify somewhat the 

 shade of blue obtained in the reaction. 



Alkaline Copper Solution. The alkaline copper solution has 

 not been changed. 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 1 liter. If the chemicals used are not pure a sedi- 

 ment of cuprous oxide may form in the course of 1 or 2 weeks. 

 If this should happen, remove the clear supernatant reagent 

 with a siphon, or filter through a good quality filter paper. Our 

 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. 



Standard Sugar Solution. Three standard sugar solutions 

 should be on hand : ( 1 ) a stock solution, 1 % dextrose or invert 

 sugar, preserved with xylene or toluene; (2) a solution contain- 



