58 Scheerer on Isomorphism. 
From the circumstance of three equivalents of water being able 
place isomorphically one equivalent of magnesia, it directly 
follows that combinations such as Mg: Si, Mg? Si-+ 3H, and 
Mg Si + 6H, must, of necessity, possess the same crystalline form. 
Such combinations therefore, under this common form, can occur 
mixed together in every possible proportion, and thereby explain 
the occurrence of non-definite proportions in the respective 
amounts of water and of magnesia, not only as met with in as- 
pasiolite and in serpentine, but also, as may be deduced from the 
sequel, in a very considerable number of other minerals contain- 
ing water. 
I. Sinicares. 
- A. Silicates of magnesia and ae bases east there- 
with, (minerals allied to serpentine. ) 
1. Gymnite. (‘Thomson. ) 
Pixygen ratio, Si; (R) = 20-86 ; 20°56. Formula deducible 
therefrom, (R)? Si. 
(R) in this mineral = 36:00 Mg, 21-60 , 0:80Ga. In addi- 
tion thereto, Thomson found in gymnite 1-16 ‘ferriferous alumina. 
Deducting this as a } silicate, the oxygen ratio given above be- 
comes modified to 20:36 ; 20- 56, approximating therefore even 
yet closer to 1; 1. 
/ 2. Deweylite. (Shepard.) 
20°78 : 21-40. (R)? Si. 
(R) = 40-0 Mg, 20:08. The siliceous hydrate of alumina 
from Baltimore has a similar composition, according to Allan 
3. Villarsite. (Dufrenoy.) 
20:47 : 21:37. (R)? Si. 
(R) from two analyses = 45-33-47-37 Mg, 4:30-3:59Fe, 2 ed 
2-42 Mn, 0:54-0-53 Ca, 0-46 K, 5-80 #2. 
4, Daihanliis (Ficinus. ) 
19°74 : 18-79. (R)? Si. 
(R) in two analyses = 23-70-19-33 Mg, 11:33-14:00 Fe, 2:25 
-1-:17 Mn, 0:83-1:83 Ca, 0:50-1:33 Na, 25-20-22 H, and in addi- 
tion thereto, 0:42-0:83 Al; deducting this latter as ! silicate, the 
oxygen ratio "a altered to 19: 44 ; 18°79, 
5. Chrysotile. (Metavite, Delesse. ) 
21-90 ; 20°60. (R)? Si. 
