597 



experiments. Without going into the detail of the inquiry, I beg 

 leave to record an observation which appears to furnish an experi- 

 mental solution to the question. 



Ethylene-diamine, when submitted to the action of iodide of ethyl, 

 yields a series of ethylated derivatives, amongst which the diethylated 

 compound has claimed my particular attention. This body in the 

 anhydrous state is an oily liquid containing 



(C.HJ"] 



C 6 H 16 N 2 = (C 2 H 5 ) 2 lN 2 . 



H 2 J 



With water it forms a beautiful crystalline very stable hydrate*, of 

 the composition 



(C, HJ" 



C 6 H 18 N 2 0=(C 2 H 5 ) 2 

 *1 2 



The vapour- density of the anhydrous base was found by experi- 

 ment to be 57*61, showing that the molecule of diethyl-ethylene- 

 diamine corresponds to 2 vols. of vapour, the theoretical density 



being 111=57. 



On submitting the crystalline hydrate to experiment, I arrived at 

 the vapour-density 33 '2. This number is in perfect accordance with 

 the result obtained in the case of ethylene-diamine. The legitimate 

 interpretation of this number is that here again the hydrated base 

 splits into the anhydrous diamine and water, and that the density 

 observed is that of a mixture of equal volumes of diamine-vapour 



and of water-vapour, the theoretical density of which is - =33. 



A 



The correctness of this interpretation admits of an elegant experi- 

 mental demonstration. 



Having observed that the hydrate loses its water when repeatedly 

 distilled with a large excess of anhydrous baryta, the idea suggested 

 itself, to attempt the decomposition of the hydrate in the state of 

 vapour. If the vapour obtained by heating this hydrate to a tem- 

 perature 1 5 or 20 higher than its boiling-point actually consisted 

 of a mixture of equal volumes of its two proximate constituents in a 

 state of dissociation (to use a happy term proposed by Deville), it 

 appeared very probable that the volume would be halved by the 

 * Proceedings, vol. x. p. 104. 



