168 METHODS FOR THE ANALYSIS OF BLOOD 



least thirty minutes, and is then filtered through a dry filter. 10 

 c.c. of this filtrate (equivalent to 2.5 c.c. of serum) are used for the 

 determination of calcium according to the method of Lyman 

 (see page 158). In this method calcium is precipitated essentially 

 according to the well known technique of McCrudden and the 

 crystals of calcium oxalate are then collected and washed by the 

 help of the centrifuge. For the determination of magnesium the 

 supernatant liquid remaining in the centrifuge tubes is collected 

 by means of a small syphon, as is also the portion of ammonium 

 oxalate solution used as wash liquid; the total amount of fluid 

 collected in this way is placed in a flat-bottomed platinum dish 

 and evaporated to dryness after the addition of 3 c.c. of 10 per 

 cent sulfuric acid; the residue in the dish is then ignited over a 

 free flame until white, an operation which should be complete in 

 two or three minutes. When cool the white residue is dissolved 

 in about 5 c.c. of distilled water, and 10 per cent hydrochloric 

 acid is added drop by drop until the solution of ash is acid to methyl 

 orange. This solution is transferred quantitatively to a 100 c.c. 

 beaker, using distilled water to conclude the operation, and evapo- 

 rated to a volume of 2 to 3 c.c.; concentrated ammonium hydroxide 

 is then added drop by drop until the solution is alkaline, and 

 finally 0.5 c.c. of 10 per cent ammonium phosphate solution con- 

 taining 50 c.c. of concentrated ammonium hydroxide per liter. 

 The beaker is covered with a watch-glass and allowed to stand 

 over night. The next day the liquid is poured into a conical 

 centrifuge tube, and the beaker washed with 20 per cent alcohol 

 containing 50 c.c. of concentrated ammonium hydroxide per liter. 

 After centrifuging, the liquid in the tube is removed by means 

 of a small siphon, and the beaker and tube are again washed with 

 about 10 c.c. of the alcohol-ammonia mixture. Three more por- 

 tions of wash liquid should be used, the precipitate being thoroughly 

 stirred after each addition of fresh liquid. 



The precipitation and subsequent washing just described are 

 essentially the process described by Marriott and Rowland in 

 their micro method for the determination of mangesium in blood 

 (see page 165, this Manual). 



This portion of the procedure is at once the most important 

 and the most unsatisfactory feature of the determination. Both 

 in the method of Marriott and Rowland and in the procedure 

 described in this paper, recourse has of necessity been had to a 



