90 METHODS FOR THE ANALYSIS OF BLOOD 



taining 2 c.c. of 0.05 normal hydrochloric acid. The rest of the 

 process is as described under 1. The only precaution likely to be 

 overlooked is that the rubber tubing used for connections needs to 

 be rinsed with water before being used the first time, and, later also, 

 if the tubing has been idle for any length of tune. The talcum 

 powder with which the inner and outer surface of rubber tubing 

 is coated is probably the source of the trouble in the case of new 

 rubber tubing. It is probably contaminated with ammonia. 



3 and 4. Urea Determination by Means of Autoclave 

 Decomposition 



To 5 c.c. of blood nitrate in a 75 c.c. test-tube is added 1 c.c. 

 of normal acid ; the mouth of the test-tube is covered with tin-foil, 

 and the test-tube with contents is then heated in the autoclave 

 at 150 C., for ten minutes. 



Allow the autoclave to cool to below 100 before opening. The 

 ammonia is then distilled off exactly as in the first process described, 

 except that 2 c.c. of 10 per cent sodium carbonate are substituted 

 for the borax, or the ammonia may be removed by aeration as 

 described in the second method. 



DETERMINATION OF PREFORMED CREATININE 



Principle. The same as that for the determination of creatinine 

 in urine. 



Procedure. Transfer 25 (or 50) c.c. of a saturated solution of 

 purified picric acid to a small clean flask, add 5 (or 10) c.c. of 10 

 per cent sodium hydroxide, and mix. Transfer 10 c.c. of blood 

 filtrate to a small flask or to a test-tube, transfer 5 c.c. of the 

 standard creatinine solution, to be described below, to another 

 flask, and dilute the standard to 20 c.c. Then add 5 c.c. of the 

 freshly prepared alkaline picrate solution to the blood filtrate, 

 and 10 c.c. to the diluted creatinine solution. Let stand for eight 

 to ten minutes and make the color comparison in the usual manner, 

 never omitting first to ascertain that the two fields of the colorim- 

 eter are clear when both cups contain the standard creatinine 

 picrate solution. The color comparison should be completed 

 within fifteen minutes from the time the alkaline picrate was 



