240 J. D. Dana on the Isomorphism and 4 
the ratio to the oy sie series of 3:2. Serpentine has 44, to 
which if one-half be added, it becomes the atomic volume very 
aauiy of copper Ahan 
Brittle Silver Ore (Sprédglaserz=6 Ag S+Sb $3) has M: M=115°39’, and one 
of its brachydiagonal prisms 72°32’; while arragonite has the corresponding angles J. 
116°10/ and 69°22 : | 
6 Ag =8100° A. 115128651771 . 
1Sb 16128 : C 1771+-16=1107 
9S 1800 : 
115128 
This result gives the ratio of 3: 1. 
We do not decide here whether these minerals are proper iso- | 
morphs or ig of the groups with which they are compared. | 
‘opaz one position has nearly the axes of chrysoberyl. 
They are oe by von Kobell as follows— 
For Chrysoberyl, 0°5800 : 1: 0-4702 
or Topaz 0:4745 : 1: 0°5281 
and the latter is the same approximately as the former reversed. 
Calculating the atomic volume of topaz (Al shale off on Si2, we find 
4Si = 2309-24 ms of elements, 55. 
6Al 3850°80 A, 8204:15+3: he, gr,) =2344-0 
2 Al 3418 CO, 2344+55=42% 
6F 1425-0 
1 Si 27731 
8204-15 
The atomic volume thus corresponds with that of the chrysolite series. 
The following are some comparisons of dimetric and hexagonal 
species, alike in the length of the vertical axis. 'The coincidences 
of atomic volume cannot be deemed scoters 
Axis. Atomic volume. 
5 Vesuvian, dimetric, 0-5345 ‘64 
Dioptase, ‘rhombohedral, 0:5295 45°44 
; Rutile, dimetric, 06555 40-7 
Arsenic, rhombohedral, 06938  163(=4x 40-75) 
Scapolite, dimetric, 0:44 54: 
Nepheline, rhombohedral, 0:4629 56°66 
ryl, 0:4993 53°46 — 
Tungsten, dimetric, 10488 50°3 
Chabazite, rhombohedral, 1:0798 515 
It is obvious that these observations are but the introduction 
to a subject of great extent, and of the widest interest to 
science. 
