292 Mr. M. Donovan on the supposed Identity of the Agent 



in order to form a comparison, the number of discharges of the 

 Dutch chemists was in effect but 42'677. But it was afterwards 

 shown by Dr. Pearson, that in these experiments not more than 

 half the quantity of electricity employed by the Dutch chemists 

 was active in decomposing the water, owing to the too great 

 distance of the conducting wires from each other within the tube ; 

 thus would their estimate be at once reduced to 21,389 discharges. 

 Faraday's estimate for the same duty is 800,000 such discharges, 

 or nearly thirty-eight times greater than that of the Dutch 

 chemists. 



In 1797, Dr. Pearson, assisted by Mr. Cuthbertson, made a 

 set of experiments on this subject with unexampled labour. In 

 the only experiment completely reported by Dr. Pearson, it ap- 

 pears that from 16,836 discharges of a jar, containing 150 square 

 inches of coated surface, he obtained almost half a cubic inch of 

 the mixed gas*. Hence 33,672 discharges would furnish almost 

 a cubic inch of the mixed gas ; and we may call 35,000 such 

 discharges equal to an exact cubic inch. Therefore to obtain 7863 

 cubic inches of the two gases, which together constitute one grain 

 of water, 275,205 discharges should be employed if the resulting 

 mixed gas were pure. But five-eighths of it only were pure ; 

 hence 440,328 discharges would be required to produce 7863 

 cubic inches of pure gas from Dr. Pearson's Leyden jar of 150 

 square inches of coated surface. Now as Pearson's discharges 

 were made from a Leyden jar of 150 square inches of coated 

 surface, while Faraday's were from a battery containing 24*4 

 square feet, when the former are converted into the latter, the 

 number of Pearson's discharges required for the decomposition 

 of one grain of water would be reduced to 18,817, which is forty- 

 two times less than Faraday's estimate. 



The estimate of Van Troostwyk and Deiman, corrected accord- 

 ing to Pearson, is 21,184 discharges for the decomposition of 

 one grain of water ; that of Pearson is 18,817; the difference is 

 2367. This is as close an agreement as could well be expected 

 in a comparison of such experiments. But the vast difference 

 of Faraday's 800,000 discharges, forty-two times greater than 

 Pearson's estimate, is very striking, and leads to some suspicion 

 of the universality of the law as laid down by that philosopher, 

 namely, that water when subjected to the influence of the electric 

 current, no matter what the intensity or the acting surface so 

 that the quantity be the same, the quantity decomposed will be 

 exactly proportionate to the quantity of electricity which has 

 passed-)-. All this may be very true when applied to the voltaic 

 influence ; but if so, the law seems to individualize common 



* Philosophical Transactions, vol, lxxxvii. p. 152. 

 t Researches, pars, 732, 726. 



