306 On the Action of Solids in liberating Gas from Solution. 



It was stated by De Luc * that water purged of air cannot 

 be boiled ; and Donny f gives an experiment in which water, 

 heated in an oil-bath many degrees above its boiling-point, 

 at length suddenly bursts into steam with the force of an ex- 

 plosion. The water, it is said, cannot boil unless air be present 

 in the liquid, because, according to De Luc's theory, or, as it is 

 now called, the theory of Clausius, air is required for the steam 

 to expand into. There is a well-known experiment by Grove, 

 in which water covered with a layer of oil was repeatedly 

 boiled, and it was found impossible to get rid of the dissolved 

 air. I repeated this experiment some years ago, and found 

 that air was carried down by the oil itself. As soon as the 

 water was fairly boiling, the oil was broken up into globules, 

 and one or more bubbles of air attached to the oil was carried 

 down into the liquid. On removing the lamp, the oil rose to 

 the surface with a ring of air-bubbles beneath. But supposing 

 all these facts to be accurately represented, and that a liquid, 

 at or near the boiling-point, is constituted like soda- or Seltzer- 

 water, then I cannot admit that a solid, such as a glass rod, in- 

 troduced into a boiling liquid (water for example), becomes 

 covered with bubbles of steam by virtue of the air carried down 

 by the rod. If the rod be unclean J (that is, contaminated with 

 a greasy film), the steam-bubbles cover it precisely after the 

 manner of the gas-bubbles, because there is adhesion between 

 the steam-bubbles and the film and not between the water and 

 the film, and hence there is a separation. A chemically clean 

 glass rod has no such action, not because the act of cleaning it 

 deprives it of its adhering air, but because there is perfect ad- 

 hesion between a vaporous supersaturated solution and a che- 

 mically clean surface. 



It is perhaps a fortunate thing for science (the object of 

 which, some people suppose, is the discovery of truth) that men 

 are so enamoured of their own theories that they defend them 

 with the strongest dialectical weapons that they can furbish up ; 

 and it is out of the battle of rival theorists that truth finally 

 emerges. So that while each man pursues science with perfect 

 honesty and sincerity, but nevertheless for his own glory, 

 Nature, like one of her own stars, ohne Hast aber ohne Rast, 



* " Quand on a prealablement purge l'eau de tout l'air qu'elle conte- 

 noit, elle ne peut plus bouiller ; et la raison en est que les vapeurs ne 

 peuvent se former qu'a des surfaces libres." — Recherches &c., Geneva, 

 1772. For authorities on some interesting points in connexion with boil- 

 ing, see " Historical Notes " &c, Phil. Mag. for March 1869. 



t Mem. de V Acad. Roy. de Bruxelles, vol. xvii. 1845. 



X In a paper contained in the Phil. Mag. for October 1868, a precise 

 meaning is given to the terms "clean" and "unclean." See also 

 Phil. Mag. for April 1873 and November 1874. 



