Chemistry and Physics. 121 
The method —— vast in bringing at the same time in a red 
hot ieineinis ape o currents, one of chlorid of tin and one of vapor 
of water. ~ wie of tin whigh results from the decomposition of the 
he 
a inet rhombic prism, while the natural mineral has the form of a 
Square prism. ‘The artificial crystals always have the two 6 meted stag 
cating faces greatly extended, so as to present forms much resembling 
Brookite artificial tin crystals have the same Lengivudioal striz, 
parallel. to the vere es of the primary. The angle of the two 
Ping: faces (13 s the same as in brookite—(e? on e°= 
Levy): thus the wae rhombic oxyd of tin is isomorphous with 
brookite. 
The natural oxyd of tin has for a long time been recognized as iso- 
morphous with rutile. It appears from these results that the two pri- 
rhom 
Bec use the artificial oxyd of tin has a form different from that of 
the e'entive mineral, we are not at liberty to conclude that the two crys- 
talline systems correspond to modes of production which are very dif- 
ferent from each other; for in the Oisans and in Switzerland, the same 
veins and often the same specimens contain at least two of the species 
of titanic acid, anatase and brookite. The conditions are iharefore 
very similar, which decide the change of molecular equilibrium, pro- 
ducing the two forms of titanic a 
vapor of perchlorid of etanfasn treated by the same methods to 
Which the chlorid of tin was submitted, gave titanic acid in little brist- 
ling mammillary masses, the mapa points perfectly sharp, but 
be microscopic dimensions. These little crystals have the form 0 
rookite 
The chlorid and fluorid of silicon, treated in the same manner in a 
here and there very small crystalline faces, among which are visible 
triangular faces like those in qua 
Srconp Seems, Vol. IX, No. 25.—Jan., 1850. 16 
