188 S. Pern: Estimation of Small Amounts of Calcium. 



pointed out that all filter-papers, even the best Swedish, contain 

 noticeable amounts of calcium. When the crucible is cool, 1 c.c. of 

 2 per cent, acetic acid is added by means of a graduated pipette 

 with rubber teat. It is stirred round with a glass rod, rinsing the 

 rod after each use. The contents are drawn up with a pipette and 

 filtered, the same care being taken by rinsing the pipette each 

 time. Another 1 c.c. of 2 per cent, acetic acid is again added to the 

 crucible, and after agitating is filtered. 0.5 c.c. of distilled water 

 is used to wash out the crucible, and then passed througli the 

 filter-papers, making a total of 2.5 c.c. in the tube. A solution of 

 a calcium salt, phosphate or chloride in dilute acetic acid is used 

 of the strength of 0.0025 grras. of calcium per 1 c.c, for controls 

 0.6. 0.7, 0.8, 0.9, 1, 1.1, 1.2 c.c. are vised, giving a wide range 

 which represents 0.015, 0.0175, 0.02, 0.0225, 0.025, 0.0275, 0.03 

 mg. of calcium. These are placed in the tubes and filled up to 

 2.5 c.c. with distilled water. 



Now all is ready for testing. 



Add 1.5 c.c. of alcohol (ordinary methylated spirits, if calcium- 

 free, will do), then three drops of a saturated solution of oxalic acid 

 with a dropper. They are all shaken as rapidly as possible, and 

 witliin a few minutes the results can be read by looking down the 

 tubes and comparing with the controls. 



A 10 per cent, variation even in such small quantities can be 

 estimated by this somewhat crude nephelometric method, and with 

 the advent of one of the new instruments finer grades will easily 

 be obtained. 



Since completing this method Mi-. H. Lyman has shown that a 

 large percentage of the calcium can be picked up by mixing the 

 blood with twice or three times its volume of a 6.5 per cent, solu- 

 tion of trichloracetic acid, and as a clinical test the following gives 

 a fair degree of accui-acy and is rapidly carried out. 



Dilute a given quantity of blood witli twice its volume of a 6.5 

 per cent, solution of trichloracetic acid and allows to stand for twenty- 

 four hours, by then there will be a clear fluid above the precipi- 

 tated proteins, 2 c.c. of this is pipetted off and neutralised till 

 faintly acid, it is transfei-red to the nephelometric tube and equal 

 quantities of methylated spirit added, then three drops of a satu- 

 rated solution of oxalic acid, and shaken. The result can be read 

 against controls within a few minutes, giving one-third of 2 c.c. 

 of blood. 



Mv thanks are tendered to your President, Professor Osborne, 

 for much advice and help during these investigations. 



