190 METHODS FOR THE ANALYSIS OF BLOOD 



of the potassium pyroantimonate is precipitated by the addition 

 of alcohol in the proportion used in the method. This is accom- 

 plished by adding to 10 c.c. of the reagent in a platinum dish 

 2 c.c. of distilled water and 3 c.c. of 95 per cent alcohol. 



Details of the Method 



Serum. The serum may be separated from the clot any time 

 within twenty-four hours after collection of the sample, as it has 

 been found that the sodium content of normal serum is not changed 

 during this time by contact with the clot. 



Platinum. The platinum dishes must be scrupulously clean, 

 otherwise the precipitate has a tendency to adhere to the sides. 

 The dishes are cleaned with fine sand, then rinsed with distilled 

 water. 



Addition of Reagent and Alcohol. No special precautions 

 are necessary for the addition of the reagent. The 95 per cent 

 alcohol has to be added drop by drop while the mixture is stirred 

 with a rubber-tipped rod. Redistilled alcohol should be used. 



Precipitation. Precipitation is complete from thirty to 

 forty-five minutes after the addition of the alcohol. 



Gooch Crucibles. The Gooch crucibles are prepared by 

 placing one layer of No. 40 Whatman filter paper in the bottom, 

 on top of this a thin layer of asbestos, then a second layer of filter 

 paper, and finally a second layer of asbestos. The precipitate is 

 so fine, however, that for the first four or five determinations 

 results will be obtained which are from 3 to 10 per cent low. After 

 this the results are generally accurate within 1 or 2 per cent. It 

 is recommended that four crucible^ be prepared as outlined above, 

 and before any quantitative determinations are made, between 

 300 and 400 mg. of sodium pyroantimonate be filtered through 

 each pad, thus clogging the pores of the filter. The sodium 

 pyroantimonate may be prepared by the addition of 10 c.c. of 

 the reagent and 3 c.c. of 95 per cent alcohol to 2 c.c. of a sodium 

 chloride solution containing from 3 to 5 mg. of sodium per cubic 

 centimeter. After standing about five minutes 60 to 100 mg. 

 of precipitate will be obtained. This is transferred to the Gooch 

 crucible and washed with 30 per cent alcohol. The procedure is 

 repeated until 300 to 400 mg. have been transferred. One set of 

 crucibles has been used over 25 times anc} at the end of that time 



