110 Scientific Proceedings, Royal Dublin Society. 
U.S., to which the formula Sp,At has been assigned ; if this be 
expanded to express approximately the results actually afforded 
by its analysis we have :—Si,,0,Al,.Mg,;Fe;H.. The molecular 
weight is 2970, and the specific gravity 2°71; the molecular volume 
is therefore 1096, or dividing by 10 (since there are 10 molecules 
in the group), 109-6, which is almost identical with that of serpen- 
tine. For the molecular weight of serpentine is 276, the specific 
gravity 2°5, and the molecular volume consequently 110. In 
view of this, and the fact that 9 out of the 10 molecules in the 
compound consist of serpentine, it would seem that not much error 
can arise if we assign to the hypothetical amesite a molecular 
volume of 110. 
There are at least two sources from which serpentine is derived, 
enstatite and olivine. The reaction in the case of the latter may be 
thus represented :— 
Olivine. Serpentine. 
28i(0,Meg), + 20H = Si,(O:Mg),(OH), + MgO. 
The molecular weight of the olivine is 280, and its specific gravity 
3°3 ; its molecular volume is therefore 85, while that of serpentine 
is 110. Thus disregarding the single molecule of magnesia on the 
right-hand side of the equation, the conversion of olivine into ser- 
pentine is accompanied by an increase of volume amounting to 
nearly 30 per cent. 
In the hydration of enstatite we have :— 
Enstatite. Serpentine. 
8 SiOMg0, + 2 OH; = Si; (0,Mg); (OH), + Si0>. 
The molecular weight of the enstatite is 300, and its specific 
gravity 3:1; hence the molecular volume is 96°8, and the increase 
of volume in passing into serpentine amounts to 13-6 per cent, 
Had the liberated silica been taken into account, the increase 
would have been found to be much more considerable, and in a 
rock consisting of olivine and enstatite it would make itself evident, 
since the magnesia liberated from the olivine and the silica from 
the enstatite might be expected to unite to form a further quantity 
of serpentine. Such a case is represented thus :— 
Olivine. Enstatite. Serpentine. 
Molecules, : 12 + 6 = 9 
Volume, . - 00 + 193°6 = 990 
