362 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



decrease in the constant. Kasterine,* and Ramsay and Shields f have 

 pushed the observations to the critical point and have shown that the 

 constant becomes zero at this point. This had been studied qualitatively 

 many times, but the above-mentioned observers have carried out quanti- 

 tative investigations. 



The vanishing of the capillary constant of the interface noticed by these 

 observers is to be attributed not to the vanishing of the constant of the 

 liquid, but to the fact that the values for the liquid and vapor have ap- 

 proached equality, causing the boundary surface to disappear. 



The capillary constant of the boundary between two liquids at high 

 temperatures and pressures, and between a liquid and the saturated vapor 

 of another liquid has not been investigated. The following research is 

 an attempt to supply to some slight extent these missing data. It will 

 be readily seen that the choice of liquids is limited, 

 if the experiments are to be pushed to temperatures 

 much above the room temperatures. The sub- 

 stances should be as nearly insoluble as possible in 

 each other, should not act upon each other chemi- 

 cally ; the vapor density of one, at least, should be 

 very small in experiments on vapors. As yet little 

 more than a beginning has been made, as the larger 

 part of the available time has been spent in devising 

 and testing the apparatus and methods. 



^y 



B 



s 



Theory of Experiments. 



The method of experimenting on the surface 

 between a liquid and the saturated vapor of another 

 liquid will be described first. The substances were 

 placed in a glass tube of the general appearance 

 shown in Figure 1. 



The part A contaius the liquid to be vaporized, 

 the part B, the liquid whose surface is to be studied. 

 C is a small capillary tube suspended inside B. 

 The surface tension is found by measuring the height 



of the meniscus in the capillary above that in the large tube, the diameters 



of the two tubes, and the ang;le of contact. Then 



Figure 1. 



* Kasterine, Journ. ile Phys. (3), 2, 529 (1893). 



t Ramsay and Shields, Phil. Trans., 184, (547 (1893). 



