232 Royal Institution. 



ciful speculations. Their principal objection, reasonable or not, was 

 that this oethyle was a purely ideal substance. From hydrochloric 

 acid, or from water, we readily procure hydrogen. We separate 

 metals from their combinations ; but oethyle could not thus be ob- 

 tained, and there was a point where it seemed that this analogy 

 failed. Frankland however has silenced this objection in the most 

 satisfactory manner, namely by procuring and isolating this oethyle. 



He prepared it by a modification of the form of experiment by 

 which hydrogen itself is prepared. He placed together zinc and 

 iodide of oethyle in tubes hermetically sealed, and heated them con- 

 siderably above the boiling-point of water. On opening the tubes, 

 the oethyle escapes as a colourless combustible gas. There is only 

 one property of oethyle on which I need dwell — its specific weight ; 

 it is about twice the weight of air. 



JEthyle, however, when procured, did not realize all the antici- 

 pations formed of it, and there was one very important difference 

 between the actual and the anticipated oethyle. It was supposed 

 that when zinc acts upon iodide of hydrogen, it takes away (so to 

 say) the iodine, and the hydrogen becomes what is termed free, and 

 the same with oethyle. On this view, oethyle would have a certain 

 atomic constitution, O H 5 . Now there is mueh reason to believe, 

 that in the gaseous form the molecules of all bodies occupy the 

 same space, whether this molecule consist of 2 only, or, as may be 

 the case, of 100 atoms. Hence to ascertain of how many atoms the 

 molecule of a substance consists, we have simply to compare its 

 weight in the gaseous form with that of some other gas of which 

 the molecule is already determined. When this experiment was 

 made with oethyle, it was found to be just twice as heavy as it should 

 be ; that is to say, the space which should have contained 2 atoms 

 of carbon and 5 of hydrogen was found to contain just twice that 

 quantity, or C 4 H 10 . 



Some chemists considered that oethyle was an exception to the 

 general rule, and that the molecule of oethyle only occupied half the 

 space of the molecule of other bodies, so that the same space which 

 contained 1 molecule of water truly contained 2 molecules of oethyle. 

 This however is evidently but an arbitrary assumption to meet the 

 case. Others said that, after all, the true oethyle remained yet to be 

 discovered, and that this body was not it, but a hydrocarbon iso- 

 meric with it, for that the real oethyle would have only half the 

 density of this body. 



There is however a third view, on which the oethyle of theory is 

 also the oethyle of fact. On a former occasion, I showed reasons 

 for believing that the elements are in a certain sense compound 

 molecular groups, consisting of 2 or more atoms, which (in the pre- 

 sent state of our knowledge) we must regard as similar, united to 

 form a compound molecule. On this idea, the gas hydrogen is 

 represented, not by the symbol H, but as HH ; and oethyle, the 

 analogue of hydrogen, would also consist of a double atom, and be 

 represented, not as C 9 H 5 , but as C 2 H 6 C 8 H*. 



The old view, however, had always a certain advantage over this, 



