Intelligence and Miscellaneous Articles. 157 



ON THE ANALOGIES PRESENTED BY THE LIBERATION OF GASES 

 FROM THEIR SUPERSATURATED SOLUTIONS AND THE DECOMPO- 

 SITION OF CERTAIN EXPLOSIVE BODIES. BY D. GERNEZ. 



I established, long since*, that, in supersaturated gaseous solu- 

 tions, the excess of the quantity of gas dissolved above the normal 

 quantity (that is, above that which the liquid would dissolve in the 

 same conditions of temperature and pressure) does not escape, if 

 no mechanical action be interposed, unless any gaseous atmosphere 

 (retained, for example, at the surface of a solid body or in the capil- 

 lary cavities of a porous substance) be introduced into the interior of 

 the liquid. It is in this atmosphere, which plays the part of a vacuum 

 in relation to the different gas dissolved, that the latter escapes 

 at the free surface of the liquid. Now the sides of vessels often 

 retain, even when they appear wet, a gaseous layer localized espe- 

 cially in the anfractuosities which are almost always found at the 

 surface of solid bodies. Hence it results that, in vessels which 

 have not undergone special preparation, supersaturated gaseous 

 solutions produce in more or less abundance bubbles of gas upon 

 the sides. But if, by washing successively with potass, boiling 

 distilled water, and alcohol, the superficial layer of glass vessels 

 (in certain points of which a small quantity of air is held) be care- 

 fully dissolved, we find that not a single gas-bubble will form on 

 the side bathed by the liquid, no more than in the interior of the 

 supersaturated solution, between very wide limits of temperature 

 and pressure. 



The emission of the gas then takes place only at the free surface 

 of the liquid ; exchanges are made from layer to layer with a slow- 

 ness such that, for instance, water saturated with carbonic acid 

 under a pressure of about 2| atmospheres, and exposed in an open 

 tube at temperatures near 8° C, is still supersaturated in the layer 

 situated at 10 centims. from the surface, even after fifty days. 



"When the pressure is lessened the gas is still emitted only at 

 the surface, if the vessel has been properly prepared. Thus water 

 saturated with carbonic acid under a higher pressure than 2| at- 

 mospheres has been very easily kept in the vacuum made with the 

 mercury pump, without one bubble of gas being disengaged at the 

 interior of the solution ; and yet the manometer of the receiver in- 

 dicated only a pressure equal to the maximum tension of aqueous 

 vapour at the temperature of the experiment. The gas escaped 

 only at the surface, without a bubble appearing, and with a rela- 

 tively feeble velocity. 



If a gaseous atmosphere be introduced into this solution at the 

 surface of which a vacuum is maintained, a lively effervescence is 

 produced which resembles violent ebullition. I have realized the 

 experiment by plunging into Seltzer water a fragment of platinum- 

 sponge or of binoxide of manganese held at the end of a platinum 

 wire : all the liquid above the porous substance was violently pro- 

 jected, while below not a bubble of gas was liberated. 



* Comptes Rendus, Nov. 19, 1866, vol. lxiii. p. 883. 



