1877.] 



Repulsion of Bubbles by Heat. 



147 



in the water-oven, and not that communicated to it by the spatula, caused 

 attraction. 



To ascertain at what temperature attraction became repulsion, and 

 vice versa, the specimen was placed upon a Strieker's hot stage, and the 

 platinum wire was heated in oil contained in a test-tube. 



A succession of experiments yielded the following notes : — ■ 



Effect cm bubble. 

 Eepulsion feeble. 



Neither repulsion nor attraction. 



5? J) 55 



Feeble attraction. 

 ?? )j 



On another occasion the wire was maintained at 100° C, and a number 

 of experiments gaye like results : — 



Temperature of crystal. Effect on bubble, 



o 



42 Feeble repulsion. 



45 Neither attraction nor repulsion. 



53 Slight attraction. 



Above and below these limits attraction and repulsion were feeble. 



I next ascertained the critical point of the carbonic acid in this cavity 

 and found it to be as low as 21° C. Prof. Andrews kindly informs me 

 that 14 per cent, of nitrogen lowers the critical point of carbonic acid 

 to about 20° 0. It is by no means unlikely that nitrogen is the gas 

 present in this cavity in something like the same proportion, and that the 

 tension is something very considerable. 



It seems to be a matter of great interest to know whether the dif- 

 ference in temperature between the attracting wire and the bubble was 

 so slight as when repulsion occurred ; the specimen was therefore 

 heated on the Strieker's stage to such a temperature as to ensure 

 attraction by a hotter body. The following is an account of the ex- 

 periments. The bulb of a fine thermometer was often used as the 

 attracting body ; at other times a platinum wire heated in mercury. 



Temperature Temperatun 

 of crystal. of wire. 



400 110 0. 



42 110 



45 110 



50 100 



52 100 



52 100 



