358 PHYSIOLOGICAL CHEMISTRY 



10 grams of Co(N0 3 ) 2 .6 aq. are added. After a day or two the 

 solution is filtered from any precipitate, K 2 Na [Co(N0 2 ) 6 ]. aq. 

 and diluted to 400 c.c. (Bray.) 



Special Sodium Acetate Solution (for Uranium Acetate 

 Method for Phosphates.) 



Dissolve 100 grams of sodium acetate in 800 c.c. of distilled 

 water, add 100 c.c. of 30% acetic acid to the solution, and 

 make the volume of the mixture up to 1 liter with distilled 

 water. 



Stokes' Reagent. 



A solution containing 2% ferrous sulphate and 3% tar- 

 taric acid. When needed for use a small amount should be 

 placed in a test tube and ammonium hydroxide added until 

 the precipitate which forms on the first addition of the hy- 

 droxide has entirely dissolved. This produces ammonium 

 ferrotartrate, which is a reducing agent. 



Toepfer's Reagent. 



Dissolve 0.5 grams of dimethylamino-azobenzene in 100 c.c. 

 of 95% alcohol. 



Uranium Acetate Solution (Standard). 



Dissolve about 35.0 grams of uranium acetate in 1 liter 

 of water with the aid of heat and 3-4 c.c. of glacial acetic 

 acid. Let stand a lew days and filter. Standardize against 

 a phosphate solution containing 0.005 gram of P 2 5 per cubic 

 centimeter. For this purpose dissolve 14.721 grams of pure 

 air-dry sodium ammonium phosphate (NaNH 4 HP0 4 . 4H 2 0) 

 in water to make a liter. To 20 c.c. of this phosphate solution 

 in a 200 c.c. beaker add 30 c.c. of water and 5 c.c. of sodium 

 acetate solution (see above) and titrate with the uranium 

 solution to the correct end reaction as indicated in the method 

 proper. If exactly 20 c.c. of uranium solution are required, 

 3 c.c. of the solution is equivalent to 0.005 gram P 2 5 . If 

 stronger than this, dilute accordingly and check again by 

 titration. 



