connected with the Boiling of Liquids, 441 



The boiling was singularly vigorous, every part of the smear 

 originating rapidly ascending bubbles of vapour, which boiled 

 over. 



Such experiments as these may be multiplied to any extent. 

 Their results seem to me to be eloquent in favour of the action 

 of nuclei in liberating vapour. Such action may be explained 

 by M. Verdet's theory, or by that of M. Gernez, or by my own. 

 I say they are active because the vapour adheres to them and 

 the water does not; but I think it can hardly be maintained 

 that their action is due to air, seeing that in the course of these 

 repeated boilings air is expelled while the nuclei continue as 

 active as ever, and it is only after twelve hours or so of repose 

 that air is reabsorbed in any appreciable quantity. 



The following cases of nuclear action are taken from a paper 

 read by me before the Society of Arts on the 7th of April, 1869, 

 entitled " On the Theory of Boiling in connexion with some 

 Processes in the Useful Arts/'' 



1. In some of the old colliery engines of Scotland, when the 

 steam becomes slack and there is no time for cleaning out the 

 boiler, the engine-men are accustomed to throw into it about a 

 bushel of the radicles of barley, produced during the malting 

 and separated in cleaning the malt. The effect of these radicles 

 (or comings as the men call them) becomes immediately appa- 

 rent on again raising the steam ; for not only is there an 

 abundant supply for producing the full working-speed of the 

 engine, but an excess going to waste at the safety-valve. This 

 singular effect will continue during several days*. 



2. In the distillation of ardent spirits on a large scale it is cus- 

 tomary, when converting the wash intowhatarecalled^lowwines," 

 to throw a lump of soap into the still every time it is charged. 

 This has the effect not only of causing the steam to rise more 

 quietly, but the vapour is more free from the residual matter of 

 the process. 



3. The sugar-boilers are accustomed to throw a lump of 

 butter into the vacuum-pan for the purpose of preventing that 

 irregular boiling which displays itself in furious bursts, separated 

 by apparently almost passive intervals. Solid paraffin is now 

 preferred to butter in producing regular boiling. 



4. Professor Oersted f noticed that if a metallic wire be sus- 

 pended in a boiling liquid, it instantly becomes covered with 

 bubbles of vapour. To show the application of this fact, 10 lbs. 

 of brass wire_, -J- of a line in diameter, were put into a still con- 

 taining ten pints of brandy ; seven pints came over at a heat 

 which, in the absence of the wire, would have sent over only four. 



* Edinburgh Philosophical Journal, O. S. vol. ii. p. 340. 

 t Gehlen's Journal, vol. i. p. 277- 



