I20 Indianapolis Biochemical Meeting: Ahstracts [Sept. 



The Determination of Calcium in the Presence of Phosphates 



and Magnesium 



F. H. MCCRUDDEN 



{Hospital of the Rockefeller Institute for Medical Research, 



New York City.) 



Summary of the results of Part I. I shall summarize the 

 results by describing details of the methods which may best be tised. 



Special solutions needed: 2^ per cent, oxalic acid Solution; 

 3 per cent. ammonium Oxalate Solution ; 20 per cent. ordinary acetate 

 Solution. 



1. The Solution containing calcium (it may also contain mag- 

 nesium and phosphate and small amounts of iron) is brought to a 

 volume of fröm 75 to 150 cubic centimeters. Concentrated am- 

 monia Solution is added drop by drop until the Solution is just 

 alkaline. This point may be recognized either by the precipita- 

 tion of calcium and magnesium phosphate, if present in any amount. 

 or by change in color of an indicator which may be added. 



2. Concentrated hydrochloric acid is added drop by drop until 

 the Solution is just acid. This may be recognized by the disap- 

 pearance of the precipitate of phosphate if present, or by the change 

 in color of an indicator. If iron is present, an indicator (alizarine 

 red) should be used, for in this case the precipitate of phosphate of 

 iron does not disappear as soon as the Solution becomes acid. The 

 change in color of the indicator and not the disappearance of the 

 precipitate is the end point in this case. 



3. Ten drops of concentrated hydrochloric acid (specific gravity 

 1.20) are added. It is best to ascertain, first, that ten drops of the 

 concentrated acid with the dropper used are equivalent to 10 c.c. of 

 n/2 hydrochloric acid within about 10 to 15 per cent. 



4. Ten cubic centimeters of 2^ per cent. oxalic acid are added. 



5. Either one of two methods of procedure may be used — a or 

 h. (a) The Solution is boiled until the precipitated calcium Oxalate 

 is coarsely crystalline,^ and then an excess of 3 per cent. am- 

 monium Oxalate should be slowly added to the boiling Solution and 



* If but little calcium is present, none precipitates at this point. 



