THE INDIVIDUAL GROUPS OF. PROTEINS 507 



The 3 -way tap of one of the bulbs (A) is connected by a piece of bent 

 capillary tubing (B) and thick rubber joints with a i c.c. pipette (C) graduated 

 in iJ^ths. The lower end of the pipette is connected by thin rubber tubing 

 to a second graduated pipette (D). The pipette -C is placed in the water-bath 

 with the flask which is being calibrated. Water is poured into pipette D 

 which is levelled so that the water reaches the zero mark of pipette C, the 

 tap of the manometer being opened to the air by removing the stopper. 

 When the temperature is constant (in about 5 minutes) the tap is replaced and 

 arranged so as to connect A with the manometer and the flask. The tap of 

 the other flask is turned so as to close it from the air. The level of the 

 manometer is read, say 9/2 cm. on each side. By raising D a volume of air 

 (25 to -4 c.c.) is slowly introduced into the apparatus and the manometer 

 is read again. Supposing '28 c.c. or 280 cmm. were introduced and the 

 manometer levels were 5-8 and 12 -6 cm., the pressure difference (/) is 



12-6 - 



6-8 cm. or 68 mm. 



280 



A correction must be made for the dead space (S) between the level of the 

 water in C and the 3 -way tap. This is determined by raising D and filling 

 the apparatus as far as the tap with water, noting the volume which runs out 

 of D. Supposing it to be 75 c.c. (= 750 cmm.), the correct constant is 



K = K -- 

 10,000 



4'12 - '075 = 4-045. 



This constant 4*045 is the constant for the empty bottle. When any 

 volume (v) of liquid is in the bottle the constant is different. Thus for 3-2 c.c. 

 of liquid (the amount generally used) the value is 



k " = k> " ~ = 4 45 " 32 = 3 ' 73 



3-73 is the working constant of the apparatus in those cases where the 

 total volume of blood plus reagents is 3-2 c.c. The constant must be 

 determined in this way for each bottle. 



Note. It is important that the bottles and stoppers on which they fit are 

 designated by some mark, as the constant so determined only applies for the 

 same bottle connected with the same side of the same manometer. Any 

 confusion in making determinations is disastrous. 



The difference in volume of the two bottles is compensated by adding 

 more ammonia solution to the larger bottle. The difference in volumes 

 (V V) in cmm. of the two bottles may be found from their constants (K and 

 K'), thus V - V = 10,000 (K - K'). 



Determination of the Oxygen Capacity of Blood. 



The bottles and stoppers of the apparatus are cleaned with hot alcoholic 

 potash, rinsed with water and dried. 



A saturated solution of potassium ferricyanide is meanwhile prepared by 

 grinding the solid with distilled water in a mortar and decanting the 

 supernatant solution. 



The necks of the bottles are greased with lard or vaselin ; 2 c.c. of 

 ammonia solution (4 parts of '880 ammonia in 1000 c.c. of distilled water) are 

 put into each bottle. 



