DETERMINATION OF C H 



421 



(2) No froth preventer is necessary or advisable. It merely acts on the 

 tap lubricant. 



(3) All quantities are reduced to 1/5 of those given above, e.g. 0-2 c.c. 

 plasma, 0-1 c.c. water, and 0-1 c.c. acid. In all, exactly 0-5 c.c. of fluid 

 is used. 



Calculation of Results. 



TABLE LXXXI. 



TABLE FOR CALCULATION OF C0 2 -CoMBiNiNG POWER OF PLASMA 

 (from Van Slyke and Cullen). 



Intermediate values may be obtained by interpolation. 



B = observed barometric pressure. 



Normal range adult 53-77 c.c., infants about 10 per cent, lower. 



44. Alterations of the Surface Tensions of Oil- Water Interface by Alter- 

 ations in Hydrogen Ion Concentration (Hartridge and Peters, Jour. Physiol. 

 LIV., Proc. XLL). Oil free from fatty acids or soaps is essential. Pure 

 olive oil, castor oil, or cod-liver oil may be freed from these bodies by boiling 

 for a number of hours with frequent changes of a considerable excess of 

 tap water. A series of test tubes 6 x 5/8" each receives 5-10 c.c. of the 

 treated oil. Into each is put a capillary tube 4" long, open at both ends. 

 The test tube is almost filled with the fluid to be tested. Try solutions 

 having a pH of 9, 8, 7, 6. Measure the height to which the oil rises in the 

 capillary. 



45. Principle of Measurement oi H-ion Concentration by Potentiometer. 

 The principle is much the same as that of the conductivity measurements 

 (Fig. 78), only instead of having a single source of potential and an unknown 

 resistance, one has known resistances and two sources of E.M.F., one of 

 which is of unknown value. 



In Fig. 78, b may be taken as a cell of standard E.M.F. sending its current 

 through the wire bridge R l - R 2 . If we lead into R 1 - R 2 the wires from 

 another battery x, taking care that the direction of the difference of potential 

 is the same, e.g. both negative poles leading to R lt as the fall of potential 

 along R l - .R 2 is regular, we can readily divide the wire so that the difference 

 of potential between the point of entrance and exit of the current from x 

 is equal and opposite to the difference of potential between the same points 

 caused by the standard cell, i.e. the galvanometer or electrometer will 



