Ixxxiv Historical Sketch of the Physical Sciences, 1818. 
hydrosulphuret of ammonia is dropped into a solution of zirconia, 
and the precipitate undergoes the same change of colour when 
exposed to the solar rays. ; 
(10.) The only re-agent which acts in a strikingly different 
manner upon solutions of oxide of titanium and of zirconia is 
the tincture of nutgalls. In the common solution of oxide of 
titanium it throws down a reddish brown precipitate, whereas in 
the solution of zirconia it occasions a deposition of yellow flocks. 
The addition of ammonia renders the colour more inclining to 
brownish red, and makes the precipitate more abundant. 
(11.) Both the solution of oxide of titantium, and of zirconia, 
have an astringent taste. 
It is obvious from this detail of particulars, that if zirconia 
and oxide of titanium be two distinct substances, as is believed 
at present, we are still ignorant of a method of separating them 
from each other.—(Schweigger’s Journal, xxi. 240.) 
»  Thishistorical sketch has extended already to so great alength, 
that I must pass over the notice of the new analyses of various 
minerals which have been inserted im the twelfth and present 
volumes of the Annals of Philosophy. 1 refer the reader to 
Annals of Philosophy, xii. 388, 465, 468 ; and xi. 65, 141, 144, 
232, 310. 
III. CRYSTALLINE FORM OF CINNABAR. 
This mineral, which is almost the only one of mercury, oc- 
curs in great abundance, but seldom in crystals. Hence its 
crystalline form had not yet been determined with accuracy. 
Haty, when he published his Mineralogy, had seen only two 
crystals, and he was led from them to suspect that the primitive 
form was a regular six-sided prism. M. le Chevalier de-Parga 
has lately sent him a set of very complete crystals of this mine- 
ral from the mine of Almaden, in Spain, which has enabled him 
to determine the primitive form, and the laws of crystallization 
of this mineral, with all the requisite precision. He has accord- 
ingly published a memoir on the subject which will be duly 
appreciated by mmeralogists. As it is scarcely possible to make 
his deductions intelligible, without the assistance of figures, I 
think it will be better to insert the memoir entire in a future 
number of the Annals. It may be sufficient to observe in this 
place, that the primitive form of the crystals of cinnabar, ac- 
cording to Hauy, is an acute rhomboid, the smallest incidences 
of the faces of which are 71° 48’, and the greatest.108° 12’. 
The ratio between the demidiagonals of each rhomb is /3 to /8. 
«Ann. de Chim. et Phys. viii. 64.) - ~ 
IV. ON THE CAUSES OF THE DIFFERENT CRYSTALLINE 
FORMS OF MINERALS. 
The great variety of forms which the same mineral speciés is 
known to assume, has drawn much of the attention, and occa- 
