282 Action of Solid Bodies on Gaseous Supersaturated Solutions. 



solution. But if the charcoal thus treated be taken out of the 

 soda-water and be placed in distilled water in a flask over the 

 flame of a spirit-lamp, the gas reassumes its elastic form, and 

 copious torrents are poured off from it during a long time. 

 When this is exhausted, steam takes its place ; and this action 

 may be continued for any length of time, the effect being to 

 prevent the bumping of the vessel, and to increase the amount 

 of vapour given off*. 



In some of Dr. Render's experiments it appears that while in 

 the same gaseous solution platinum had scarcely any action, 

 silver became coated with numerous bubbles. The reason simply 

 was that the platinum happened to be clean and the silver un- 

 clean. So also on gently heating a solution of ammoniacal gas 

 (liquor ammonia;), no bubbles were formed either on platinum 

 or silver. The reason was that the alkali made their surfaces 

 clean. But if a platinum wire be drawn between the finger and 

 the thumb previously touched with a fatty body, such as lard, 

 the wire becomes abundantly covered with bubbles on introdu- 

 cing it into the solution of ammonia in a test-tube held over a 

 spirit-lamp so as to warm it gently. The same result may be 

 obtained with an aqueous solution of nitrous oxide under the 

 receiver of an air-pump, a slight diminution of pressure being 

 sufficient for the purpose. 



Dr. Henrici obtained no result on placing an oil or a solid 

 fattv body, such as stearine, on the surface of soda-water. Had 

 he dipped a clean glass rod into oil, or rubbed it with stearine, 

 he would have found it become abundantly covered with bubbles 

 on immersing it in soda-water. 



The fact is, that in an inquiry of this kind we cannot form 

 clear ideas unless we distinguish and classify the bodies used 

 according to the nature of their surfaces. And in this respect 

 bodies may be arranged into three or four classes, in the first of 

 which we place glass and all vitreous or vitrified surfaces, and the 

 denser metals with a smooth non-porous surface, such as plati- 

 num, gold, silver, iron, steel, lead, tin, and mercury. To all 

 these bodies, when chemically clean, the gaseous supersaturated 

 solution adheres in the most perfect manner, so that there is no 

 separation of gas at their surfaces. 



In the second class we may place oils, both fixed and volatile, 

 and fatty bodies, whether acid or neutral, various kinds of wax, 

 resin (such as shellac and amber), camphor, phosphorus, and 

 some other bodies, which, when chemically clean and placed in a 

 gaseous supersaturated solution, display a very different kind of 

 adhesion to one of its constituents as compared with the other ; 



* "On the Action of Solid Nuclei in liberating Vapour from Boiling 

 Liquids," Proc. Roy. Soc. 1869, p. 240. 



