Royal Institution. 233 



in the clear and consistent account which it gave of the mode of 

 formation of hydrogen. How is it, it may be asked, and by what 

 process, that this compound atom of hydrogen is formed? The 

 answer is by no means obvious. Indeed the investigation of the 

 nature of the process by which aethyle was formed alone gave the 

 key to its solution. 



iEthyle is not, in truth, made by the direct action of ziuc upon 

 the iodide of aethyle ; but by the intervention of another body, which 

 belongs to the class of what I may term fugitive or evanescent com- 

 binations, and which is made and decomposed again in the course 

 of the experiment. This body is zincaethyle. The molecule of zinc, 

 consisting of 2 atoms, ZnZn, splits into two parts. 1 atom, Zn, 

 combines with the iodine of the iodide of aethyle, C 2 H 5 1, to form 

 iodide of zinc, Znl, while the other atom at the same moment com- 

 bines with the aethyle, forming zincaethyle, Zn C 2 H 6 . 



The mode of action of zincaethyle upon iodide of aethyle is per- 

 fectly analogous to its action upon water. In contact with water, 

 HHO, it immediatelv decomposes, forming hydrated oxide of zinc, 

 ZnHO, and hydride of aethyle, OH 5 H. This hydride of aethyle 

 has hardly more than half the density of the aethyle gas. In the 

 same space in which, in the other case, are contained 2 heavy atoms 

 of aethyle, are here contained 1 heavy atom of aethyle and 1 light 

 atom of hydrogen. Now the zincaethyle with the iodide of aethyle 

 decomposes in a perfectly similar manner, forming iodide of zinc, 

 Znl, and aethyle gas, C 2 H 5 C 2 H*. That this is truly the mode of 

 the formation of the aethyle is proved by the fact, that by careful 

 modification of the experiment, it is possible to break up this pro- 

 cess of the formation of the aethyle into the two factors (so to say) 

 of which it consists*. At a low temperature the zincaethyle alone 

 is formed. At a higher temperature the zincaethyle disappears, and 

 the aethyle is produced. 



It is evident that the formation of the compound molecule of hy- 

 drogen, HH, must be a very different physical event to the forma- 

 tion of the single atom of hydrogen, H, if such could exist. The 

 ordinary hypothesis of the "liberation" of hydrogen gives us no 

 conception of its nature : we need some other explanation. 



It seems to me probable, that when zinc acts on hydrochloric 

 acid and water, there are, as in the case of aethyle, two steps in the 

 process, — the first, the formation of a zinchydrogen, ZnH ; the 

 second, the action of this zinchydrogen on the water, with the 

 formation of hydrated oxide of zinc, ZnHO, and hydrogen gas, HH. 

 There are various arguments in favour of this view. First, it ex- 

 plains the result, which the other hypothesis does not. Secondly, 

 the analogy of aethyle compels us to it. It is not probable that 

 bodies so similar in other respects are dissimilar in the mode of 

 their formation. Thirdly, there is at least one experiment in which 

 we are absolutely able to analyse the process of the formation of 

 hydrogen, and to prove that it does take place in this manner. 



This remarkable experiment is the formation of hydrogen by the 



* See Quarterly Journal of the Chemical Society, vol. iii. p. 405. 



