Dr. Hofmann on anomalous Vapour-densities. 159 



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 — — =5/. 



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. 



2i 



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 15° 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 

 introduction of anhydrous baryta. Experiment has verified this 

 anticipation. 



The upper half of a glass tube 

 filled with, and inverted over, mer- 

 cury, was surrounded by a second 

 glass tube open at both ends and of 

 a diameter about treble that of the 

 former, the annular space between 

 the two being closed at the bottom 

 of the outer tube by a well-fitting 

 cork. The vessel thus formed round 

 the upper part of the inner tube 

 was moreover provided with a small 

 bent copper tube open at the top 

 and closed at the bottom, which 

 was likewise fixed in the cork. The 

 vessel being filled with paraffin and 

 a lamp being applied to the copper 

 tube, the upper part of the mer- 

 cury-tube could be conveniently 

 kept at a high and constant temperature, whilst the lower end, 

 immersed in the mercury-trough, remained accessible. A glance at 

 the figure explains the disposition of the apparatus. A small quan- 

 tity of the hydrated base was then allowed to rise on the top of the 

 mercury in the tube ; and the paraffin bath having been heated to 

 170°, the volume of the vapour was observed. Several pellets of 



