MICROCHEMICAL METHODS FOR BLOOD ANALYSIS 299 



ture down the double portion of the filter paper and withhold- 

 ing the remainder until the whole filter has been wet. Then the 

 whole of the mixture is poured on the funnel and covered with 

 a watch glass. If the filtration is made as described the very 

 first portion of the filtrate should be clear as water and no re- 

 filtering is necessary. 



It will be noted that the precipitation is not made in vol- 

 umetric flasks. By the process described 6 or 7 or 11 or 12 c.c. 

 of blood can be used, whereas with volumetric flasks one is com- 

 pelled to use 5, 10 or 20 c.c. because flasks suitable for other 

 volumes are not available. Special graduated * ' blood pipettes, ' ' 

 made by Emil Greiner Co., New York, are very useful for the 

 measurement of the blood, the tungstate and the acid. 



The protein blood filtrates are not acid enough to prevent bac- 

 terial decomposition. If the filtrates are to be kept for any 

 length of time, more than two days, some preservative, a few 

 drops of toluene or xylene should be added. 



Nonprotein Nitrogen Determination. (Folin and Wu: 

 Jour. Biol. Chem., xxxviii, 90, 1919). The acid digestion mix- 

 ture is made as follows : Mix 300 c.c. of phosphoric acid syrup 

 (about 85% H 3 POJ with 100 c.c. of concentrated sulfuric acid. 

 Transfer to a tall cylinder, cover well to exclude the absorption 

 of ammonia, and set aside for sedimentation of calcium sulfate. 

 This sedimentation is very slow, but in the course of a week or 

 so the top part is clear and 50 to 100 c.c. can be removed by 

 means of a pipette. (It is not absolutely necessary that the 

 calcium should be thus removed, but it is probably a little safer 

 to have it done.) To 100 c.c. of the clear acid add 10 c.c. of 6% 

 copper sulfate solution and 100 c.c. of water. Two c.c. of this 

 solution are substantially equivalent to 1 c.c. of the acid solu- 

 tion previously described by Folin and Denis. 



Introduce 5 c.c. of the protein-free blood filtrate into a dry 

 75 c.c. test tube graduated at 35 c.c. and at 50 c.c. Add 1 c.c. 

 of the sulfuric-phosphoric acid mixture described above. Add a 

 dry quartz pebble and boil vigorously over a microburner until 



