166 METHODS FOR THE ANALYSIS OF BLOOD 



small casserole or a platinum dish and used for magnesium deter- 

 mination. The calcium oxalate remaining in the centrifuge tube 

 is dissolved in 0.5 c.c. of concentrated nitric acid. This is best 

 accomplished by first adding the acid and then 5 or 10 c.c. of water; 

 the tube is then heated by immersion in a beaker of hot water 

 and the contents are stirred by bubbling air through the tube by 

 means of a capillary glass tube reaching to the bottom of the 

 centrifuge tube and connected with a rubber bulb. The contents 

 of the tube are then transferred to the beaker and evaporated to 

 a volume of about 5 c.c.; the calcium is then reprecipitated and 

 determined exactly as described above. 



The liquid syphoned off into the dish contains the magnesium J 

 present, to this is added 0.5 c.c. of concentrated sulfuric acid, and 

 the liquid is evaporated to dryness on an electric stove. Ashing 

 is completed over a Me"ker burner. If a small amount of black 

 residue remains, a drop of sulfuric acid is added, after cooling, 

 and the ashing repeated. To the residue is added 0.5 c.c. of con- 

 centrated hydrochloric acid and a little water. The dish is warmed 

 and the contents are transferred to a small (25 c.c.) beaker with 

 several washings of hot water. The beaker is put on an electric 

 stove and the contents are evaporated to a volume of about 3 c.c., 

 a drop of phenolsulfonephthalein is added, and then 1 c.c. of 

 ammonium phosphate solution. 2 1 c.c. of concentrated ammonia 

 is run in with stirring and the beaker allowed to stand over night. 

 Crystals of ammonium magnesium phosphate separate out on the 

 sides and bottom of the beaker. 



The contents of the beaker are transferred to a conical 15 c.c. 

 centrifuge tube and centrifuged for a couple of minutes. The 

 liquid is syphoned off in the manner above described and the pre- 

 cipitate in beaker and tube washed with 10 per cent ammonia 

 (one part concentrated ammonia to nine parts of water), the pre- 

 cipitate in the tube being stirred up each time with the capillary 

 blowing tube. It is unnecessary to dislodge the precipitate from 



1 Approximately 0.2 c.c. of liquid remains in the centrifuge tube, and this 

 amount, which is about 2 per cent of the total, may be allowed for in the final 

 calculation, if extreme accuracy is desired. 



2 Ammonium phosphate solution is made as follows: 25 gms. (NH4) 2 PO 4 

 are dissolved in 250 c.c. H 2 O. 25 c.c. of concentrated ammonia are added 

 and the mixture is allowed to stand over night. The following day it is 

 filtered, the filtrate is boiled to remove the excess of ammonia, cooled and 

 made up to 250 c.c. 



