. Chemistry. 185 
ing to Haiiy, it crystallises in the form of a rhombohedron, in 
which the ratio of the diagonals of the transverse section are as 
S to 4. The obtuse angle of this section, is 102° 38^, and the obtuse 
angle of the principal section 110° 38'.~Note by M. Mariano de 
Rivero in the Annales des Mines ^ 1821, tom. vi. p. 596. 
30. Analyses of different hinds of Mica. — M. Peschier of 
Geneva has analysed several different kinds of mica, and has 
discovered Titanium in this mineral. The following are his re- 
sults, with three kinds of mica, with one axis of double refraction : 
Green Mica 
Black Mica 
Foliated Black 
of Vesuvius. 
of Vesuvius, 
Mica of Siberia. 
Silica, , - 45. T 
42.0 
35.5 
Alumina, - 31.7 
8.35 
11.25 
Magnesia, - 0.95 
Lime, - 10.75 
15.7 
lion, - 6,8 
8.35 
16.0 
Titanium, - 0.1 
15.0 
30.0 
Soda, 
8.5 
1.7 
Lithion, 
2.5 
Potash, 
6.1 
In the first and third of these varieties. 
a trace of manganese 
was found. M. Peschier has 
also discovered titanium in the 
white mica of Siberia, and in 
the mica 
of Massachussets. — 
Journ. de Phys. xciii. p. 241. 
31 . Analysis of Alum. — The following 
are the results of Dr 
Thomson’s analysis of alum : 
4 Atoms Sulphuric Acid, 
20.0 
or 32.8542 
3 Atoms Alumina, 
6.75 
11.0882 
1 Atom Potash, 
6 
9,8562 
25 Atoms Water, 
28.125 
46.2012 
otherwise. 
3 Atoms Sulphate of Alumina, 
21.75 
or 35.72885 
1 Atom Sulphate of Potassa, 
11.00 
18.06975 
25 Atoms Water, - - 
28.125 
46.20123 
Dr Thomson conceives that there is no evidence of there being 
any bisulphate of potash in dhim.— Annals of Philosophy^ vol. iii. 
p. 168. 
32. On the Heat developed in solutions Crystallised by Ex- 
posure to the Air. — When 51 parts of sulphate of soda and 49 
parts of water are placed in a phial, and the stopper removed in 
