Atomic Volume of some Minerals. 239 
We have added several acknowledged isomorphs that the na- 
ture of the series may be understood, preparatory for comparison 
with the other species. This series is, 
116° 10’ 117°13’ 117°19 118°30/ 
43 506 50°54 57°3 
In the above series there is a change of 14:3 in atomic volume 
for a change of 2° 20’ (or 140’) of angle. This is equivalent very 
nearly to 0-1 for 1’. The differences between the first and second 
in this series and between the third and fourth correspond nearly 
with this rate. 
To appreciate the relation of atomic volume between nitrate of 
potash, and the other species of the series, we compare it with 
witherite which is nearest it in angle, and find the ratio nearly of 
3: With reference to bournonite, we should compare with 
arragonite, which is nearest it in angle; or perhaps more correctly 
with a number still smaller than the atomic volume of arragonite, 
since the angle is nearly a degree less. The true ratio we cannot 
decide upon without further investigation. 
We observe that the atomic volume in the arragonite series in- 
creases with the angle while, as shown by Kopp, it diminishes in 
the calc series. Moreover the species with a prismatic form have 
a higher atomic volume than the rhombohedral; and in the 
Species calc spar the two series overlap. 
Zn 6 Mg Mn tad Poe Sr 6 Ba 
107946’ 107925’ 10790’ 106951’ 105°15’ 
35°65 86°25 37°70 40°1 46°24 
43° 506 5054 573 
116°10’ 117918’ 117919’ 118°30/ 
We should hence expect that if either of these species were 
dimorphous like cale spar, it would be those nearest to calc spar. 
The species chrysolite and those of that series differ from ar- 
ragonite in havin : M=119° — 120°, and as the angle of the 
arragonite series enlarges, the erystallization of the two approxi- 
mates. The atomic volume of the chrysolite series varies from 
40 to 46, and this is near arragonite. 
e add here the calculations for two species, one of which 
approaches chrysoberyl and the other arragonite. 
Copper glance (€u8) has M:M=119°85’, and a brachydiagonal prism =125°40’, 
while chrysobery] has M : M=119°51’ and a brachydiagonal prism ==130°. 
€u = 793-2 A. 993°2+5°7 (sp. gr.) =174 
200: C. 174—8=58 
9932 [or if €u is a single atom, 174-267] 
As 2Cu is isomorphous with 1Ag and other metals, the last value 
of the atomic volume appears to be most correct. This gives 
