attending the Efflux of condensed Air and Steam. 331 



ruptly start open, the action being accompanied by a peculiar 

 sound indicating the ejection of drops of water from the tube 

 through which the air is escaping. It would be a curious fact 

 if the sound thus occasioned were proved identical with that 

 which Dr. Schafhaeutl mentions as uniformly accompanying 

 the development of electricity in his experiments on the 

 steam evolved from a Marcet boiler. This sound, however, 

 often occurs after the electricity has appeared, but it is uni- 

 formly the signal for the electroscope to open when the de- 

 velopment has not previously taken place. I cannot say that 

 I have ever noticed a similar noise in any of my experiments 

 on steam. 



I am wholly at a loss for an explanation of these singular 

 phaenomena. It is well known that a copious precipitation of 

 vapour, and a greatly accelerated evaporation, are the simul- 

 taneous effects of the sudden dilatation of condensed air in a 

 receiver— the precipitation being caused by the extreme cold 

 produced by expansion, and the increased evaporation by the 

 diminution, which the precipitation occasions, of the quantity 

 of transparent vapour contained in the air— and to the agency 

 of these two principles I was at first inclined to attribute the 

 effects in question, conjecturing that the variation in the 

 kind of electricity developed in the receiver, might be owing 

 to the predominance, sometimes of evaporation, and some- 

 times of precipitation. The remarkable influence of heat 

 and moisture, and the effect of a slow evacuation of the re- 

 ceiver, by which precipitation is known to be prevented, seem 

 to point out the connexion of the phaenomena with one at least 

 of the principles I have named; but I find so much difficulty 

 in accounting for many of the effects I have recently observed, 

 by reference to both or either of these causes, or to any other 

 cause I can think of, that I am at present unable to form any 

 opinion on the subject, 



I now come to the second division of this paper, and shall 

 commence with a description of the evaporating apparatus 

 which I used in the experiments on effluent steam. 



This apparatus was constructed under my own directions 

 for the especial purpose of experiment, for which it is much 

 better adapted than a steam-engine boiler; although from 

 the smallness of its size it is not calculated to exhibit effects 

 equally brilliant. It consists, chiefly, of a strong cylindrical 

 boiler, and a stove, in which the boiler is placed vertically, in 

 such a manner as to be exposed on all sides to the heat of the 

 fire. The boiler is thirty inches deep and four inches wide 

 in the inside, and is made of the alloy of copper and tin, 

 usually called gun-metal. The stove is supported upon glass 

 legs to insulate it. 



