Mr.W. G. Armstrong 07i the Electricity of Effiuent Steam. 5 



plete dilution by water (see vol. xix. pp. 25 and 179). Hence 

 K O . S Og in combining with S O3 had disengaged the same 

 quantity of heat as if the free acid had been fully diluted, and 

 hence much more than an atom of water could. Hence 

 K O . S O3 and H O are not thermometrically equivalent, as 

 Graham's theory should require. 



The total quantity of lieat evolved by the formation of 

 K O + 2 S O3, M. Hess represents as made up of the following 

 quantities : — 



K O, evolves by combining with water x units. 



SO3 510 



K O and S O3, each fully diluted with water,"! . ^ 

 evolve by combining with each other j 



A' + 917\ 



K O. S O3 combining with S O3 510J 



If we place the numbers which represent the quantities of 

 heat between the symbols of the bodies which evolve it, we 

 have K O . .r + 917 S O3 . 510 S O3. 



To know with certainty the place of the water in the for- 

 mula of the hydrated salt, we must estimate the quantity of 

 heat evolved by its union, but it is so small that the exact de- 

 termination is very difficult. If we term it .y . then the ex- 

 pression becomes K O , a; + 917 S O3 . 510 S O3 . 3/ H O. 

 The dry salt is therefore K. O + 2 S O3, and the ordinary salt 

 (KO + 2SO3) -H HO. 



M. Hess concludes with some observations on the necessity 

 of a knowledge of the quantity of heat evolved by the com- 

 bination of every essential element of a compound, to a cor- 

 rect knowledge of its theoretical nature, and suggests the de- 

 termination of the relation between the quantities x and 917, 

 and 510 and y as an object of additional researches. 



II. On the Cause of the Electricity of Effluent Steam. By 

 Wm. George Armstrong, Esq.'^ 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 A FTER an interval of several months, I have lately re- 

 -^^ sumed my experiments on this curious subject, and have 

 at length ascertained, that the flace where the excitation of 

 electricity is effected, is that at which the steam is subjected 

 io friction. 



In reflecting upon many of the experiments of which I have 



[* On the subject of this paper see Phil. Mag., 3rd series, vol. xviii. pp. 

 93, 9J, 100.— Edit.] 



