210 T. S. Hunt on the Constitution 
type as the red silver ores, and it is to compare them with it, that 
we have multiplied the received formulas. of these species by six. 
Taking then 508 for the volume of bournonite, the formula of 
arragonite may be written C3«Cas0Oo0 with a volume of 510°; 
witherite is C22Baz2Os«=503°8, while strontianite is C2sSres 
75 =505, and cerusite has the same type and volume. Bromlite 
is represented by C2s5(Cai2-sBai2-s)O75 with a volume of 500, 
and barytocalcite, the monoclinic form of the species, gives for 
the same formula 507-5. Nitrate of potash with the formula 
Nio.sKi0.sOc3 has a volume of 506. 
From the fact that it is here found necessary to assign a frac- 
tional value ton in the formulas of the nitrates and carbonates, 
we are led to infer that the equivalent weights here assumed, 
are as yet too low, and must at least be doubled. We however 
retain for the present, the fractional equivalents, and subjoin the 
‘formulas and calculated volumes of the two series. 
Rhombohedral Species. 
woe Density. | Volume. 
Proustite, AseAgisSs6 ‘ 546 
Pyrargyrite, } SbsAgisSs6 5°80 564 
Soda-nitre NisNaisO90 __ 2:26 564 
Calamine, C4oZns00120 4:45 560 
Magnesite, ) CaoMga0O0120 * 3:00 560 
Dolomite, Cs6(MgisCais)O108 2:90 554 
Spathic rom | Cs6FessO108 3°80 547 
Diallogite, C36(Mns2Ca25Mg1.5)O108 | 3:59 563 
Calcite, Cs0Cas00s0 2°12 5555 
C2sCa2sOs4 2°52 | 592 | 
Trimetric Species. 
Density. Volume. 
Bournonite, Sbs(€usPbi2)Sa6 585 | 508 
Potash-nitre, Nio-sK10-sO63 2°10 506 
rragonite, Cs0CasoOs0 2-93 510 
Strontianite, C2s5Sr25sO075 3°65 505 
erusite, C2sPb25O075 6:60 505 
Bromlite, C2s(Ba12 5Cai2-s)O75 3-71 500 
Witherite, C22Ba22066 430 | 504 _ | 
An interesting example of homology is afforded in the tout- 
malines whose composition has been well shown in the late ad- 
mirable series of analyses by Rammelsberg. The ordinary rhom- 
bohedron of this species gives R: R 133° 26’ (132°—134°, 
Breithaupt,) but the rhombohedron 2R has the angle 103° 21’, 
or nearly that of calcite. Rammelsberg has analyzed thirty va 
rieties of this species, all of which yield boracic acid in quanti- 
ties varying from six to nine per cent., and from 1:3 to 27 per 
