and Equivalent Volume of some Mineral Species. 209 
To the above series of isomorphous species, Rose has added 
soda-nitre, which has R : R. 106° 33’, light red silver ore, proustite, 
having R : R. 107° 36’, and dark red silver ore, pyrargyrite R: R 
108° 18’. Soda-nitre N Na Os with a density of 2-26 (P. and 
Joule) gives 37-6 for its equivalent volume; proustite (Ag S)s 
+As8$3, with a density of 5-5, gives 91, while pyrargyrite, in 
which antimony replaces the arsenic of the last formula, has a 
density of 5-8 anda volume of 94. 
This series then presents wide variations in volume, and it is 
only by adopting more elevated equivalent weights, that a simple 
relation becomes apparent. We shall endeavor to fix these 
equivalents as before from the densities of the species. The for- 
mulas of the silver ores are to be multiplied by six, for a reason 
which will be assigned farther on, and we have then for the for- 
mula of proustite, AgisAssSse with a volume of 546, while the 
antimonial species, and soda-nitre N:sNa1sQoo have each a vol- 
ume of Calamine then becomes CacZnaoQieo, with a . 
volume of 560, magnesite being the same. Dolomite Cs6(Cars 
Mgis)O10s gives a volume of 554, and spathic iron CacFess 
O10:=547, while the diallogite of Kapnik is represented by Cs 
(Mns2Ca2sMgi-s)O10e, and with a density of 3°592, has a vol- 
ume of 563. Calcite of the density 2°72, and the formula Cs 
Cas0Qoo0, gives 555°5 for its volume, while that with a density 
of 2:52, may be represented by C2sCa22Os4, with a volume of 
552. With these formulas it is apparent that there may be a 
great number of intermediate species from partial substitutions. 
According to the above formulas, we have in the rhombohedral 
carbonates, several genera belonging to a homologous series of the 
first kind. These genera have the same volume, and are repre- 
sented by the general formula n C2M.Oc ; that of the nitrates is 
NMOzg, and light red silver ore As Ag2Sc=assAgeSc, so that 
the general formulas of these three groups offer a very interesting 
resemblance, which was first pointed out by Gerhardt ;* they are 
The arragonite group is not less worthy of notice, and Rose 
has shown that potash-nitre and bournonite are isomorphous with 
these prismatic carbonates. The density of this series is greater 
than that of the last; Rammelsberg’s formula for Bournonite is 
(3euS, SbS2)+2(3PbS, SbS2) which equals (€usPbe)Sb3S1s; 
this with a density of 5°85, according to recent determinations 
by the same chemist, gives a volume of 254, which we double 
mpare with the volume of piperine, and with that adopted 
for leucite and the alums. Bournonite has the chemical 
*( des Tray. de Chimie, 1849, p. 322. _ 
Seconp Serres, Vol. XVI, No. 47.—Sept., 1853, 2% 
