| Scheerer on Isomorphism. 189 
Art. XVII.—Upon a peculiar bind of Isomorphism that plays 
an important part in the Mineral Kingdom; by Professor 
Scueerer of Christiania 
(Continued from p. 73.) 
i. Borares. 
1. Datholite. 
None of the prior formule for datholite agree so well with 
its composition as that brought forward by Rammelsberg, namely, 
2Ca* Si+B* Sit +3H. 4 
This formula, however, involves the improbability that the 
boracic acid is here viewed in the light of a base combined with 
the silica. This improbability may however be got over by 
writing the formula as follows: a Si+Ca R]+(R) Si, wherein 
therefore, (R)=3H. 
: 2. Botryolite. 
Rartihiislebeae formula for this mineral is, 
2Ca* Si+B* Si+6 H, 
which admits of conversion to 3[Ca §i+Ca B]+(R)? Si. 
Ill. Prosewares. — 
A. Phosphates of Iron. 
1. Vivianite. 
According to Stromeyer’s analysis, the vivianite of St. Agnes 
in Cornwall, eonsists of phosphoric acid 31°8125, protoxyd of iron 
41-2266, water 27:4843 =99-8934. 
Hitherto all endeavors have been in vain to arrive at a formula 
that would represent in a satisfactory manner the results of this 
analysis by so celebrated an analyst as Stromeyer, and which was 
appatently conducted with such precision. Von Kobell’s for- 
mula, which gives the closest ee to the result, 
Fe? > 48H, requires a composition of Pactentim acid 28°69, 
protoxyd of iron 42-38, water 28-93 = 100-00. 
This differs not immatterially from the result of the analysis, 
and mnoreoren involves a ratio in the quantity of oxygen contain- 
ed in the base, the acid and the water, which in a compound of 
so little complicated a nature can hardly be looked upon as prob- 
able. On calculating the water in Stromeyer’s a base 
isomorphous with protoxyd of iron (3H= ae which, after the 
Seconp Series, Vol. VI, No. 17. —Sept., 1848. 
