MAGNESIUM IN BLOOD 167 



the sides of the beaker. The washing is repeated four times, 

 each time with from 6 to 10 c.c. of ammonia. The precipitate is 

 finally washed once with 95 per cent alcohol made just alkaline 

 with ammonia. This is syphoned off and tube and beaker are 

 dried in an air oven at about 60 C. 



After drying, the contents of beaker and tube are dissolved in 

 10 c.c. of 0.01 N hydrochloric acid and an aliquot portion is 

 pipetted off for colorimetric determination. 



The colorimetric comparison is done in the same way as in the 

 calcium determination with the exception that the thiocyanatc 

 solution used is diluted to 40 or 50 c.c. instead of to 25, a standard 

 solution of magnesium ammonium phosphate 1 is used instead of 

 one of calcium oxalate, and dilutions in the Nessler tubes are 

 made with 0.01 N hydrochloric acid. The calculation of results 

 is as follows: If 2 c.c. of serum were used and a 6 c.c. aliquot 

 portion of the solution of the precipitate were taken, and the color 

 found to be the same as that of 3.2 c.c. of the standard magnesium 

 solution, then 



3.2X0.01 X-V-X^HP = 2.66 mg. magnesium per 100 c.c. of serum. 



MAGNESIUM IN BLOOD 



Method of Denis 2 



Principle. Magnesium is determined in the filtrate of blood, 

 or plasma (after removal of calcium by Lyman's Method, see page 

 158, this Manual), by precipitation of the magnesium as magnesium 

 ammonium phosphate and the nephelometric estimation of the 

 phosphate by means of a strychnine molybdate reagent. 



Procedure. 5 c.c. of citrated plasma, serum, or whole blood 

 are measured into 15 c.c. of 6.5 per cent trichloroacetic acid solu- 

 tion, and after shaking the mixture is allowed to stand for at 



1 This solution is made by dissolving 0.102 gm. of air-dried magnesium 

 ammonium phosphate (MgNH 4 PO4-6H 2 O) in 100 c.c. of 0.1 N hydrochloric 

 acid and diluting to 1 liter with water. Of this solution 1 c.c. is equivalent 

 to 0.01 mg. of magnesium. Magnesium ammonium phosphate loses water 

 of crystallization when heated and must therefore be dried at room temper- 

 ature. Commercial preparations of the salt are generally unreliable; it should 

 be prepared by precipitation of pure solutions. 



2 Denis: Jour. Biol. Chem., 1920, 41, 363. 



