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PROCEEDINGS OP THE AMERICAN ACADEMY. 



not a vapor spreads out on another liquid depends on the values of the sur- 

 face tension of the liquid, of the condensed vapor, and of the interface ; 

 i. e., when the liquid from the condensed vapor wets or spreads out over 

 the second liquid, the vapor will be condensed even when the tempera- 

 ture is above the saturation temperature. In order to keep such a surface 

 dry, the temperature must be maintained several degrees higher than the 

 saturation temperature. This makes observation with such a pair of 

 substances very difficult. In the earlier parts of the experiment several 

 months were spent determining whether this condensation was due to 

 the above-mentioned phenomenon or to unequal heating, bringing about 

 a distillation. The appearance of the condensation was always noticed 



100 120 HO 160 180 200 220 240 



Figure 12. 



by the change in shape of the meniscus. Ethyl ether and glycerine, while 

 serving admirably in every other way for experiment, belong to the 

 second class of substances. The condensation was very rapid as the 

 critical point of ether was approached, and the following very curious 

 effect was noticed. After the critical point had been passed by several 

 degrees, the liquid ether had entirely disappeared in the ether part of the 

 tube, while in the glycerine part of the tube liquid ether still persisted 

 and appeared to be permanent, though no trial was made for a long period 

 of time. The temperature was pushed several degrees higher and all 

 liquid ether disappeared ; then the temperature was lowered gradually 

 and liquid ether appeared first in the capillary above the glycerine, then 

 in the outer tube above the glycerine, and finally in the ether tube. 



