Mr. C. Hockin on a Lecture- Experiment. 



299 



of anhydrous sulphate of zinc directly formed in the element ; 

 for, were this the case, the quantity of heat thus confined 

 would be 9553 instead of 6000 thermal units. Moreover, if 

 it be admitted that the hydratation of sulphate of zinc and its 

 complete solution constitute a distinct phenomenon, completely 

 independent of the phenomena directly produced in the voltaic 

 circuit, it must be conceded that the inverse phenomenon of the 

 dehydratation of sulphate of hydrogen (which would absorb 8821 

 thermal units) is equally independent ; from which it would fol- 

 low that the quantity of heat confined within the element would 

 no longer be about 6000, but rather 9553-8821, or 732 ther- 

 mal units. 



As regards the quantity of heat which the work of the adjust- 

 ment of the molecules may require, it is so small that it may be 

 neglected. 



The concentration of the liquids, their nature, the distance of 

 the plates immersed, do not exert any considerable influence on the 

 distribution of heat in the circuit, and therefore do not modify its 

 resistance to any appreciable extent. The influence of the extent 

 of surface of the plates immersed appears to be much more pro- 

 nounced. Although I am not in a position to publish now all the 

 results of my experiments, I think I may state, in conclusion, that 

 the phenomena produced in the couples, and the actions produced 

 in the interpolar circuit, may be completely explained by a cal- 

 culation of the vires vivse destroyed and the motive force produced. 



XXXV. Note on a Lecture-Experiment. 

 By C. Hocktn, M.A .* 



THE little apparatus shown in figs. 1 and 2, arranged by Dr. 

 Matthiessen and myself, p-„ j 



was lately exhibited at the Royal (Scale one-tenth of the natural size.) 

 Institution. The object of the 

 apparatus is to show the identity 

 of the conducting-power of the 

 metals for heat and for electri- 

 tricity. In fig. 1 we have a 

 number of glass bulbs with 

 tubes attached dipping into a 

 coloured solution, forming a 

 series of electrical air-thermo- 

 meters. In each bulb is fixed 

 one of the wires to be compared. 

 The ends of these wires are sol- 

 dered to thick copper wires pass- 



* Communicated by the Author. 



