298 PHYSIOLOGICAL CHEMISTRY 



Reagents required for the precipitation of the proteins : 



1. A 10% solution of sodium tungstate. Some sodium tung- 

 states, though labeled c. p. are not serviceable for this work. 

 They usually contain too much sodium carbonate. The c.p. 

 sodium tungstate made by the Primos Chemical Company, 

 Primes, Pa., is satisfactory. 



2. A two- thirds normal sulphuric solution, 35 g. of concen- 

 trated c.p. sulphuric acid diluted to a volume of 1 liter, will 

 usually be found to be correct; but it is advisable, indeed neces- 

 sary, to check it up by titration. The two-thirds normal acid 

 is intended to be equivalent to the sodium content of the tung- 

 state so that when equal volumes are mixed substantially the 

 whole of the tungstic acid is set free without the presence of an 

 excess of sulphuric acid. The tungstic acid set free is nearly 

 quantitatively taken up by the proteins and the blood nitrates 

 obtained are therefore only slightly acid to congo red paper. 



Transfer a measured quantity (5 to 15 c.c.) of oxalated blood 

 to a flask having a capacity of fifteen to twenty times that of 

 the volume taken. Lake the blood with seven volumes of 

 water. Add one volume of 10% solution of sodium tungstate 

 (Na 2 W0 4 , 2H 2 C) and mix. Add from a graduated pipette or 

 burette, slowly and with shaking, one volume of two-thirds 

 normal sulphuric acid. Close the mouth of the flask with a 

 rubber stopper and shake. If the conditions are right, hardly 

 a single air bubble will form as a result of the shaking. Let 

 stand for 5 minutes; the color of the coagulum gradually 

 changes from bright red to dark brown. If this change in color 

 does not occur, the coagulation is incomplete, usually because 

 too much oxalate is present. In such an emergency the sample 

 may be saved by adding 10% sulphuric acid, one drop at a time, 

 shaking vigorously after each drop, and continuing until there 

 is practically no foaming and until the dark brown color has 

 set in. 



Pour the mixture on a filter large enough to hold it all. This 

 filtration should be begun by adding only a few c.c. of the mix- 



