CALCIUM IN BLOOD 163 



oxalate solution is not found. On the other hand some samples 

 of nitric acid contain appreciable amounts of calcium. 



Preparation of Solutions. Standard Calcium Oxalate Solution. 

 The standard calcium oxalate solution is made by dissolving 

 0.0630 gm. of pure oxalic acid (H 2 C 2 4 -2H 2 O) in water. To 

 this are added 200 c.c. of N hydrochloric acid and sufficient 

 calcium chloride solution to correspond to 20 mg. of calcium. 

 The whole is made up to 1 liter with water. One c.c. of this solu- 

 tion is equivalent to 0.02 mg. of calcium as calcium oxalate. 



Ferric Thiocyanate Solution. The ferric thiocyanate solution 

 is made from two solutions which are mixed one-half hour before 

 use. Solution A is 0.3 per cent ammonium thiocyanate. Solu- 

 tion B is 0.3 per cent ferric chloride, made up from the salt with 

 its contained water of crystallization, adding a few drops of acid, 

 if necessary, to clear the solution. Five c.c. portions of Solutions 

 A and B are mixed and the whole is diluted to 25 c.c. with water. 

 This is the proper dilution for use with ordinary serum, but when 

 smaller amounts of calcium are present the solution should be more 

 dilute; with larger amounts it should be more concentrated. 



CALCIUM IN BLOOD 



Method of Kramer and Howland 1 



Principle. The blood serum is ashed. The calcium is precip- 

 itated by a procedure which in principle is identical with that of 

 McCrudden. A definite amount of 0.1 N oxalic acid in 0.05 N 

 sulfuric acid equal to about four times the equivalent of calcium 

 present is added. The final volume is made up to 2 c.c. and an 

 aliquot of the filtrate is titrated with 0.01 N potassium perman- 

 ganate. 



Procedure. 1 or 2 c.c. of serum or plasma are measured into 

 a platinum crucible, evaporated to dryness on the water bath, and 

 dehydration is completed in the oven at 110 C. The crucible is 

 then placed in a quartz dish over a Meker or Fisher burner. It is 

 heated gently at first and then more vigorously. The outer dish 

 is then covered with a quartz plate and the heating continued 

 until ashing is complete. The platinum crucible is then removed 

 and the ash dissolved in a small quantity of N HC1. It is 

 1 Kramer and Howland: Jour. Biol. Chem., 1920, 43, 35. 



