1877.] 



Repulsion of Bubbles by Heat. 



141 



These numbers were confirmed by using the tube of water as a source 

 of heat. 



I have ascertained by experiment that at very slight elevation beyond 

 the ordinary temperature a plug of water is apparently repelled from the 

 surface of a glass tube. Mr. Sang has made similar observations. 



A capillary tube, open at both ends, had a short column or plug of 

 water within it, free to move in either direction. A warm body applied 

 to the liquid repelled it with great force, even in opposition to gravita- 

 tion. The warmth of the fingers (in other words, a rise of 21° C.) is quite 

 sufficient to drive the liquid up a tube held in a vertical position. By 

 sealing water in capillary tubes bubbles are formed which contain very 

 little, if any air ; these are likewise attracted by heat. When experi- 

 menting on the bubbles in natural cavities it was found that an increase 

 of 44° to 49° C. was required to produce the same effect ; but the fact 

 must be taken into account that the heat was more difficult of application 

 to the rock- section than to the capillary tube. 



When the tube approaches § of an inch internal diameter, the glass 

 may be heated to redness at a point in close proximity to the water 

 without causing motion ; the water is, however, instantly converted into 

 steam without previous warming, which causes a sort of slight explo- 

 sion. 



If this experiment be made in smaller tubes of ^ inch internal 

 diameter the repulsion is easily caused, and may be seen ; but a very high 

 temperature causes the repelled liquid to be evaporated and scattered in 

 drops at a further distance along the tube. 



The liquid is not repelled in a body as a liquid, but gradually as a 

 vapour. If it had only the space of a bubble to condense itself in, the 

 bubble would be attracted in the same way as carbonic-acid bubbles. 



The attraction of bubbles in cavities which contain water may be due 

 to two causes : — 1. At low temperatures, as, for instance, at 21° C, to a 

 repulsion of the liquid from the glass ; 2. At high temperatures, such as 

 60° and 70° C, to evaporation and condensation on opposite sides of the 

 bubble. 



The movements of bubbles in Iceland spar noticed by Mr. Sang 

 may thus be explained, for in that substance water-cavities are of con- 

 stant occurrence. There is no necessity to assume what seems, from my 

 observations on some hundreds of specimens of Iceland spar, to be highly 

 improbable, namely, that the liquid is carbonic acid. The mineral is so 

 soft and so easily split along its planes of cleavage, that I doubt whether 

 microscope sections could contain a liquid of such high vapour-tension. 



The following rocks contained bubbles in water-cavities which were 

 attracted by heat: — Granite from the Mourne Mountains; Aberdeen 

 granite ; quartz from Snowdon ; quartz-porphyry from Pwlheli, North 

 Wales ; granite from Ludgvan and St. Leven, Cornwall. Many other 

 specimens contained immovable bubbles. 



