1877.] 



Repulsion of Babbles by Heat. 



145 



experiments were made with the view of ascertaining the temperature 

 producing repulsion and attraction respectively in the different canities 

 of this specimen. 



Repulsion to the extreme end of the cavity, entirely in opposition to 

 the effect of gravitation, was produced by a temperature of 5° C. above 

 that of the specimen. Attraction in opposition to gravitation in cavity 

 D became active by a rise of 5° C. ; in B 14° C. were insufficient to do 

 more than give a lateral motion to the bubble. On cavity C 12° C. acted 

 energetically. 



A series of experiments were made on bubbles which contained liquid 

 carbonic acid as well as gas. 



By heating the specimen above the critical point of the carbonic acid 

 we know something of the conditions uuder which subsequent experi- 

 ments may be made. We know that the liquid is water containing a 

 gas-bubble under a pressure of not less than 109 atmospheres. The 

 following are facts which, like those preceding, were recorded at the 

 moment of observation. Fig. 4 represents a cavity in rock-crystal with 

 carbonic acid in the liquid and gaseous states floating upon water. The 

 bubble is so easily movable that it shifts about like the bubble in a 

 spirit-level. The stage of the microscope holds the section in a vertical 

 position, and when one end of the cavity is raised ^ a degree Centigrade 

 in temperature, the bubble is driven to the opposite extremity ; if the 

 specimen be turned over, this will happen in spite of the buoyancy of 

 the bubble. The bubble takes up its original position on cooling. 

 When the specimen is uniformly heated above the critical point of 

 carbonic acid, repulsion by heat still takes place. I have repeated this 

 experiment during the last twelve months an immense number of times, 

 both with fine jets of warm air and with platinum wires, always with 

 the same result. Auother exactly similar cavity being under examina- 

 tion, heat was applied by means of a hot wire spatula. When the edge 

 of the spatula was seen to approach, there was an instant repulsion 

 of the bubble from the upper to the lower end, and the liquid carbonic 

 acid was vaporized. After removal of the source of heat, the bubble 

 did not rise (i. e. apparently sink) to its original position until after 

 the liquid had condensed again ; it then slowly moved back. This ex- 

 periment was repeated again and again with other bubbles in the same 

 specimen, and notes were made each time to secure a truthful record. 

 The action in every case was precisely the same ; repulsion occurred, and 

 the bubbles sank under a uniformly diffused rise of temperature. In 

 another specimen of rock-crystal were seen two cavities, one containing 

 water only, and the other water with carbonic acid ; the bubble in the 

 latter cavity was repelled by heat (no experiment was made to ascertain 

 whether it sank on warming), but that in the water-cavity was attracted. 

 In order that there might be no possible mistake about this, the two 

 cavities were brought into the field of view at the same time, and the 



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