1913.] A Study on the Action of Surface Tension. 531 



The hydrocarbon oil was employed in two ways : as an emulsion with the 

 aqueous solution or as droplets, which, being lighter than the solution in which 

 they were liberated, were allowed to ascend through a long vertical column of 

 the solution. In the first instance a definite quantity of the oil was mixed with 

 a known quantity of the solution and the mixture agitated for some hours 

 in a shaking apparatus. The droplets of oil in the resulting emulsion were 

 of approximately like diameter, which was in a large number of cases 

 measured under the microscope. The average volume of each was determined, 

 and from this and the total quantity of oil used the united surface areas of 

 all the droplets present in the emulsion were calculated. The qiiantity of 

 the solute in the emulsion, apart from that on the surfaces of the droplets, 

 was ascertained by the application of the drop-pipette or stalagmometric 

 method. As the concentration of the original solution was known, the 

 difference between it and that ascertained stalagmometrically was the amount 

 condensed on the united surface areas of all the droplets. 



In the second method the hydrocarbon oil was allowed to ascend in 

 droplets through a long column of the solution in a cylinder which 

 terminated above in a broad cup-like receptacle. The apparatus was so 

 arranged that the connection between cylinder and receptacle formed of 

 rubber tubing could be cut off by a pressure clip. The oil droplets could 

 freely ascend to the interior of the receptacle, but the flow of the contents 

 of the latter back into the cylinder was reduced to a minimum. The 

 quantity of oil used was known, and the total number of droplets which 

 ascended through the column of liquid was determined from an average of 

 counts made for several selected test periods. When the droplets had all 

 ascended the connection with the cup-like vessel above was cut off by 

 compression of the rubber tube below it, and the concentration of the fluid 

 in the cylinder, whose volume was known, was determined. The difference 

 between this concentration and that originally present, the total volume in the 

 cylinder, and the united surface areas of all the droplets were the factors from 

 which was deduced the concenttation of the solute on each cm. 2 of surface area. 



When mercury instead of hydrocarbon oil was used, the droplets, all 

 uniform in size, fell through the fluid in a cylinder which ended below in 

 a reservoir from which it could be cut off by the closure of a glass tap. 

 As the volume of the mercury used was known and the number of droplets 

 also ascertained through an average of the counts made for that purpose, 

 the united areas of the surfaces of all the droplets were determined. The 

 original concentration and volume of the solution being known and the 

 final concentration ascertained, the amount of the solute condensed on each 

 cm. 2 of the surface area of the droplets was calculated. 



