180 METHODS FOR THE ANALYSIS OF BLOOD 



Ammonium Oxalate, 0.5 Per Cent. 



Ammonium Stearate Reagent. Dissolve 4 gms. of stearic 

 acid and 0.5 c.c. of oleic acid in 400 c.c. of hot alcohol. Add 20 

 gms. of ammonium carbonate dissolved in 100 c.c. of hot water 

 and allow the mixture to boil for a few moments. Cool. Add 

 400 c.c. of alcohol, 100 c.c. of water, and 2 c.c. of ammonium 

 hydroxide (sp. gr. 0.9). Filter. This solution should be as clear 

 as freshly distilled water and perfectly colorless. If well stoppered 

 it keeps indefinitely. Before using for analysis, test as follows: 

 Into two flasks pipette respectively 10 and 5 c.c. of the calcium 

 oxalate standard and to the 5 c.c. add 5 c.c. of nitric acid, 0.05 N. 

 Treat both with 25 c.c. of the ammonium stearate reagent and 

 read on the nephelometer. If they do not read exactly 2 to 1 

 there is some impurity present in the chemicals used. The alcohol 

 if, as is usual in laboratories, it has stood in a wooden barrel will 

 give a yellow coloration with ammonia and will contain suspended 

 particles which reflect light in the nephelometer. It should be 

 redistilled with a little calcium carbonate. Stearic acid may be 

 purified by recrystallizing from boiling alcohol. Ammonium car- 

 bonate may be resublimed. 



Calcium Oxala.te .Standard, 10 c.c. to contain 0.2 mg. of Cal- 

 cium in 0.05 N HNOz. Dissolve 72.9 mg. of pure calcium oxalate 

 (CaC2O4+lH2O) in 25 c.c. of nitric acid, 2 N, and make up to 

 1000 c.c. with water. Since the presence of chlorides affects the 

 solubilities of calcium soaps, nitric acid is used as a solvent through- 

 out instead of hydrochloric. 



CALCIUM OF THE BLOOD 



Method of Marriott and Howland l 



Principle. The protein blood serum is destroyed by heating 

 with strong nitric acid. The calcium is then precipitated as 

 calcium oxalate dissolved in hydrochloric acid and determined 

 colorimetrically by means of standard oxalate solutions. 



Procedure. 2 c.c. of clear serum are measured into a 50 c.c. 

 conical beaker, 10 c.c. of concentrated nitric acid are added, and 

 the beaker is heated on an electric stove just below the boiling 

 1 Marriott and Howland: Jour. Biol. Chem., 1917, 32, 233. 



