386 Mr. C. Tomlinson on the Action of Solids and 



such as antimony, and crystalline metals such as bismuth, which 

 contain a good deal of occluded gas. The strong adhesion be- 

 tween the gases and the pores of bodies in this class may be stri- 

 kingly exhibited by placing one of them in soda-water, when it 

 becomes apparently saturated with the gas, whilst more gas seek- 

 ing to precipitate itself upon the innumerable surfaces already 

 occupied gives rise to the appearance of a stream of gas con- 

 stantly ascending from the porous surface until the liquid seems 

 to be exhausted ; but the action may be renewed by reducing 

 the pressure or raising the temperature. In the latter case, 

 when the gas is expelled and the liquid is at or near its boiling- 

 point, it is constituted exactly like the soda-water, which may be 

 called an aqueous supersaturated solution of CO 2 , while the 

 other may be termed an aqueous supersaturated solution of 

 steam"*. A strip of aluminium (If inch by f inch) cleaned by 

 being rubbed between two corks in the strongest oil of vitriol, 

 and rinsing in water, was active in disengaging gas from soda- 

 water ; and when taken out and put into water over a spirit- 

 lamp, it liberated such copious streams of vapour, when the 

 water boiled, as to be supported vertically on one of its long 

 edges, while innumerable bubbles issued from both sides, and 

 continued to do so for about a minute after the lamp had been 

 removed. When taken out and cooled in cold water and again 

 transferred to soda-water, it was as active as before in occluding 

 and liberating gas. 



The fourth class of bodies are those w T hich are soluble in water, 

 and act by lessening the adhesion between the gas and the w T ater, 

 as when powdered white sugar is put into a glass of sparkling 

 Moselle wine. A piece of gamboge in soda-water is also a good 

 example of this class, while bodies so little soluble as phosphorus 

 and iodine belong to it. 



The results obtained with all four classes of solids in their 

 action on soda-water may, with proper precautions, be obtained 

 with aqueous solutions of ammonia, of hydrochloric acid, of chlo- 

 rine, and of nitrous oxide, and also with liquids at or near their 

 boiling-points. 



Next as to the effect of friction. It has long been known to 

 chemists that certain saline solutions^ which show no disposition 

 to deposit crystals, may be started into crystalline action by rub- 

 bing the inside of the vessel below the level of the solution with 

 a glass rod. This effect is produced although every part of the 

 arrangement be chemically clean ; and it has not, so far as I 



* This definition is given in a paper read before the Royal Society, 

 January 21, 1869 (Proc. Roy. Soc. vol. xvii. p. 240), "On the Action of 

 Solid Nuclei in liberating Vapour from Boiling Liquids." I may state 

 that Professor Schrotter (Pogg, Ann, vol. cxxxvii.) accepts this definition, 



