Mr. W. G. Armstrong on the Electricity of Effluent Steam. 25 



And from hence the heat produced by mixing sulphuric acid 

 of any strength, with an excess of water, may be computed. 



In extending these researches to the combinations of other 

 bodies than water with sulphuric acid, M. Hess arrived at 

 the remarkable result, that when a combination takes place the 

 quantity of heat evolved is constant, 'whether the combination be 

 direct or indirect ,• whether it takes place at once or by successive 

 stages. This principle is supported upon evidence derived 

 from an extensive series of experiments, to the description of 

 which we shall now pass. 



[To be continued.] 



III. Further Experiments on the Electricity of Effluent Steam. 

 By W. G. Armstrong, Esq** 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN pursuing my experiments on this subject, I observed that 

 the tendency of the steam cloud to evolve negative, instead 

 of positive electricity, gradually increased as I continued to 

 use the apparatus, until at length positive electricity rarely 

 appeared in the jet, even when circumstances were most fa- 

 vourable to its development. 



Conceiving that this gradual predominance of negative elec- 

 tricity in the steam might possibly be owing to the progressive 

 oxidation of the metal in contact with the water, I examined 

 the interior of the boiler; but no change appeared to have 

 taken place in the surface of the metal, which was in the rough 

 state in which castings come from the mould. I then washed 

 out the boiler with water, but upon using it again the elec- 

 tricity of the steam remained negative as before. After this 

 the boiler was washed out with a solution of potash, by which 

 means I was agreeably surprised to find the positive electricity 

 of the jet was completely restored. This remarkable result 

 led me to try the effect of dissolving a little potash in the 

 water from which the steam was generated, and by so doing 

 the quantity of electricity was amazingly increased; so much 

 so, that I was enabled to obtain from the apparatus upwards 

 of thirty sparks, half an inch long, in a minute. 

 * See our preceding volume, p. 328. 



