392 Transact ions. — Chemistry. 



would, I tliink, be proper for Mr. Highton to determine tlie quantity of this 

 gas which can be liberated from a certain weight of carbon by the means 

 I have indicated before assigning a limit to it in the manner he has. In 

 regard now to the " experimentum crucis " which Mr. Highton suggested to 

 me for settling the question, viz., " to keep renewing the sulphuric acid " (of 

 the battery of his just described) " till all sulphides accidentally present must 

 be fully decomposed, and seeing whether evolution of sulphuretted hydrogen still 

 went on." Upon the theory (not yet exploded) as to the infinite divisibility 

 of matter, and owing to the length of time which would be necessary to 

 detach by this means the bulk of the gas in question from the centre of the 

 carbons used, I might with propriety decline to allow my theory upon this 

 subject to stand or fall by the results of such an experiment. I have, however, 

 tried the experiments more for relative than absolute results, and, as I expected, 

 found a well-marked diminution in the yield of sulphuretted hydrogen as time 

 proceeded. 



This diminution is manifested very conspicuously to prepared lead paper 

 when held over the battery. At first this is rapidly blackened, but after 

 twenty-four hours have elapsed a light brown tint only is communicated after 

 it has been in contact one hour with the gas evolved, and when the acid was 

 renewed, the zinc cleaned, and the battery allowed to work another six hours, 

 lead paper suspended in the same position as before did not manifest a 

 change in colour for twelve hours ; and so, making renewals of acid, but still 

 retaining the same carbon pole, I at last got the evolution of sulphuretted 

 hydrogen so far reduced that even when the battery was in good action it 

 required two days' contact of the test paper with the gas issuing from the 

 battery in order to get an indication of the presence of sulphuretted hydrogen. 

 As above inferred, I do not expect that this gas could ever be wholly removed 

 from a plate of carbon by this process, but I think my results show that it is 

 given oflf in constantly diminishing quantity, no matter how often we renew 

 the sulphuric acid, and this is all I contend for, as it shows clearly that this 

 acid cannot be the source of the sulphur of the H2S given ofi*, as Mr. Highton 

 asserts, since it is obvious that were it so the gas should be given oflf in 

 quantities nearly uniform for equal times. 



Regarding the supposition that nascent hydrogen in carbon pores should, 

 according to the analogy of other chemical facts, form, with sulphuric acid, 

 water and sulphuretted hydrogen, I am at a loss to know what facts are 

 referred to by Mr. Highton, and therefore cannot debate this point. T 

 admit, however, that porous carbon or platinum is capable of exercising 

 decomposing and recomposing effects upon certain substances by what is 

 termed provisionally catalytic action ; but there is a line above which this 

 action Ls not exercised, and it seems to me that the decomposition of sulphuric 



