VITAL PHENOMENA 



59 



101 H 





Charts showing the hydrogen ion concentration of the stomach (on the 

 ordinate) and time after eating (on the abscissa). Curves 1-4 from 

 same man with different quantities of food. Curve 14 is the average 

 curve for infants. 



is air, and the drop is hence allowed to drop out of the pipette 

 into the air. The diameter of the dropping surface = 4.6 to 5.7 

 mm (J. L. Morgan, 1915). One form of pipette is Traube's 

 (1904) stalagmometer. In its use, the weight of the drop is 

 found by multiplying the volume of the drop by its specific grav- 

 ity, the volume of the drop found by dividing the volume of the 

 pipette by the number of drops from one filling. The pipette is 

 standardized with water, whose surface tension is taken as unity. 

 Therefore the surface tension = 



specific gravity of solution X no. of drops of water 



number of drops of solution 

 Traube's (1912) viscostagmeter is a dropping burette with which 

 the volume of say ten drops is measured, and is more rapid than 

 the stalagmometer, which holds forty to 100 drops of water. 

 (Stalagmometers are made to order by Kimball Durand Co., 

 Chicago.) 



It is the presence of the substance in the surface film which 

 lowers the surface tension, but it is not until diffusion into the 

 surface film has reached an equilibrium that the lowest surface 

 tension is present. For instance, soap very greatly lowers the 

 surface tension of water, but when measurements are taken 

 on new surfaces by the instantaneous method of Rayleigh, the 

 surface tension of the soap solution is found to be the same as 



