m/WtS^d^Qnthe JFfedtof VkkiicalCmMrMtM 271 



Hhiatkln taking place at the same time, a positive logs' bf*ti^iii|)e- 

 rature ought to result ; and it occurred to me that the decom- 

 position of water by the galvanic battery might be an expeti- 

 mentum crucis. I forgot, however, the heat that is produced by 

 the resistance offered to the current in passing through the 

 water. Still, on consideration, I saw that the experiment would 

 prove whether decomposition occasioned loss of heat or not; for 

 although heat is given out by the resistance, might not the 

 amount of that heat be greater if no decomposition accompanied 

 it ? If the idea I adopted were correct, net only should such be 

 the case, but the difference should be the amount of heat the 

 liberated gases would give if again chemically combined. And 

 now the problem w^as to find, whether the heat produced by a 

 galvanic current passing through water was what was due to the 

 resistance offered, or whether decomposition made it less, and 

 how much less ? ^^ 



(9.) The manner in which I endeavoured to solve this questioil 

 was as follows : — 



Having set a battery, consisting of twelve DanieFs cells, copper 

 cylinders 5 inches high, 3 inches in diameter, with brown paper 

 diaphragms and amalgamated zinc, into action as one series, I 

 noted to what distance the needle of a tangent galvanometer 

 moved when the current passed through the copper ring, which 

 was 12^ inches in diameter. I then included in the circuit a 

 volta-electrometer holding acidulated water, and again noted to 

 what division of the scale the needle moved, the current having 

 passed through the fluid in the electrometer with the decompo- 

 sition of the w^ater. The difference of the tangents of the angles, 

 when the electrometer was included and when it was not, showed 

 the resistance the water offered to the current. I now removed 

 the electrometer, and in its place introduced a fine platina wire 

 of such a length as offered the same resistance to the current 

 that the water did, which I knew by the needle of the tangent 

 instrument being equally deflected by both. I had therefore 

 two substances offering the same amount of resistance, and con- 

 sequently developing the same amount of heat ; but in one case 

 decomposition was present, in the other it was not. What, then, 

 was the result ? Exactly what I anticipated — the heat liberated by 

 the passage of the current through the water was less than that pro- 

 duced by its passage through the wire, and to the same amount that 

 the gases given off would develope if again chemically combined. 



(10.) I tested the truth of this result by many experiments 

 varied in different ways, both as to the quantity and intensity 

 of the current, the amount of resistance aijd the duration of the 

 experiment, and in every case met with a similar result. The 

 details, therefore, of one or two experiments will suffice. 



