on [Gaseous] Supersaturated Solutions. 189 



test-glass. Fragments of carbonate of soda, saltpetre, common 

 salt, &c. descended in concentrated streams visible to the eye. 

 During this descent and before the solution had time to accu- 

 mulate at the bottom of the jar and diffuse through the liquid, 

 numerous bubbles separated on introducing a glass rod or silver 

 wire ; and this continued long in action, although only very small 

 fragments of the salt were used. On using caustic alkali on air- 

 impregnated water, there arose an opaque cloud of the finest 

 bubbles as the saline streams descended ; and this cloud slowly 

 ascended and disappeared. The further course of the experi- 

 ment was as with the other salts. This experiment was tried 

 with water that had been boiled ; but it is needless to add that 

 nothing followed. 



The well-known phenomenon will be remembered, where an 

 effervescent wine, in which, after standing some time, bubbles 

 no longer rise, foams when the glass is struck or agitated, and 

 slight condensations of gas appear on the surface. If a blow be 

 struck on the side of the glass with a rod of wood, bubbles 

 immediately appear at the point struck. 



De Luc referred these phenomena to the film of air which 

 covers all bodies exposed to the atmosphere. There certainly 

 are cases in which, on immersing solids in air-impregnated 

 water, bubbles are produced in this way — as, for example, when 

 the surfaces are such as not to be wetted by the water. I have 

 made many experiments with dry, green grass halms, slightly 

 rough on the surface, which show this result. On immersing 

 them in supersaturated gaseous solutions, they became covered 

 with innumerable bubbles, especially in the more extended air- 

 spaces, such as the fine furrows &c. ; such air-spaces remain 

 longer in water exposed to the air ; while such water may not 

 give a single bubble to a metal surface. The air is evidently 

 derived from that which is carried down during the immersion of 

 the halm. All porous bodies act in the same way -when immersed 

 in liquids. Ripe grass halms with smooth surfaces behave like 

 solids generally ; they produce only a few bubbles. 



It would doubtless be very interesting to carry out an exhaus- 

 tive experimental inquiry into the cases 1 and 2, since they do 

 not involve insuperable difficulties. In the meanwhile I cannot 

 help offering a few remarks. Let us begin with the second case, 

 and consider the phenomena which arise when the attraction 

 between a solid surface and the gas in an aqueous solution pre- 

 vails. In this case the first effect can only be the condensa- 

 tion of the gases on such surface — the very opposite to a sepa- 

 ration. The adhesive attraction is but a preliminary step to the 

 chemical, with which a condensation of the less dense consti- 



