304 On the Decomposition of Water by Charcoal. 



preceding Number of the Annales, M. Figuier adduces an 

 example of the explosions which sometimes take place in 

 soap-works, which he ascribes to the hydrogen cas mixed 

 with atmospheric air, existing in the interior of the 

 vat, above the caustic lixivium ; and he explains the for- 

 mation of this gas, by supposing that the sulphurets which 

 crude soda contains, set free a quantity of hydrogen ex- 

 ceeding that which is necessary for the formation of the 

 hvdrogenated sulphured when we treat this kind of soda 

 with water. 



We know that when an alkaline sulphuret is put into 

 water, the latter is partly decomposed. A sulphate is 

 formed, and the hydrogen set at liberty is combined with 

 the remains of the sulphur and the base, in order to form a 

 hydrogenated sulphuiet. We know also that in this ex- 

 periment there is no extrication of gas if we operate at a 

 low temperature. 



Hence it is evident that the hydrogen gas which swims 

 over the soap-maker's ley, does not proceed from the de- 

 composition of the water by the alkaline sulphuret. 



I have been led to ascribe the production of this gas to 

 the charcoal always met with in the soda of commerce, by 

 a remark which I made several months ago. I had ob- 

 served that potash purified by lime, which had been long in 

 contact with vegetable substances, and which was strongly- 

 coloured by the charred substances which it had taken up 

 from them 4 , when fused in a crucible, gave out a great deal 

 of gas which took fire spontaneously ; and when the alkali 

 was red hot, its combustion resembled that of hydrogen 

 gas. 



It appeared to me on reading the memoir of M. Figuier, that 

 the hydrogen of which he speaks might have been pro- 

 duced by a nearly similar cause. I made some experiments 

 on this subject, and the object of this note is to detail the 

 results. 



The potash, on which I made the first observation, be- 

 sides charred substances, also contained a quantity of water, 

 the more considerable, as it had not been reddened in the 

 desiccation 5 and all circumstances being favourable, it ap- 

 peared tome that the carbonic acid might have been formed 

 in this case by the resulting attraction of charcoal for oxy- 

 gen, and of potash for this acid ; and that the hydrogen gas 

 must have been extricated pure or carburelted. 



In order to ascertain if this was really the case, 1 distilled 

 in a stone retort, potash similar to that which I had used in 

 the crucible : in an instant the heat was sufficient to drive 



off 



