Mr. Vincent on the Formation of Sulphide of Aluminium. 127 
~ have approximately 
=1°421, 
hence 
mA SI 
=0°6315. 
On the contrary, for those compound gases whose volumes 
during combination have been diminished, y is greater, and con- 
sequently i less ; and, in fact, it is less the smaller the volume 
of the combination compared with the sum of the volumes of its 
constituents, the latter being all considered gaseous. 
Thus is corroborated what was before stated, that the vis viva 
of the translatory motion does not alone represent the whole 
quantity of heat in the gas, and that the difference is greater 
the greater the number of atoms of which the several molecules 
of the combination consist. We must conclude, therefore, that 
besides the translatory motion of the molecules as such, the 
constituents of these molecules perform other motions, whose vis 
viva also forms a part of the contained quantity of heat. 
Zurich, January 5, 1857. 
XII. On the Formation of Sulphide of Aluminium. 
By Cuartes W. Vincent, Assist. Lib. Royal Institution*. 
HE sulphide of aluminium has hitherto been prepared by 
the action which its components exert on each other when 
brought into contact at a high temperature. In the process 
described below, I have endeavoured to effect the same object by 
the deoxidation of sesquioxide of alumina by the monosulphide 
of sodium. 
Monosulphide of sodium} was gently heated in a porcelain 
crucible to the fusing-point (when it acquires a flesh-coloured 
hue), powdered alumina was then gradually added, the whole 
being constantly stirred until the mass began to acquire a pasty 
consistence ; the crucible was then closed and the temperature 
gradually raised to a dull red heat, at which temperature it was 
kept for about half an hour. On allowing to cool and then 
extracting with water, a yellow solution was formed containing 
soda, and the excess of sulphide of sodium together with a small 
quantity of alumina. The greater part of the last, however, 
* Communicated by the Author, 
+ Prepared by passing sulphuretted hydrogen through a solution of 
caustic soda and itlowinig the sulphide of sodium to crystallize out. 
