372 Examinatiou of Mineral Substances. 
The analytical result shows that, on account of the insuffi- 
cient quantity of carbonic acid, the alumina and the oxide of 
iron must act the parts of an acid and be considered as form- 
ing an aluminate with part of the magnesia. This is the view 
taken of it by Professor G. Rose, who gives the mineral the 
formula (3 Mg, C) + (2 Mg; Al) + 24H. As this mineral 
is different in composition from any other, it has been named 
Hydrotalcite, on account of its similarity in its physical cha- 
racters to talc, from which however it is easily distinguished 
by the water it contains. 
Analysis of Steatite from Snarum. 
The composition of the steatite on which the foregoing mi- 
neral was found, is— Containing Oxygen. 
Magnesia...-..-. 37°52 «.... 14°52 
Silicic acid ....... 32°03 ..... 16°63 
AVGMINIs. o cra. 5, amos, See i 
Peroxide of iron... 4°48 f° °"°"* sis 
WV StET Gants ec POLO cen my me 
102°74 
If it is attempted to arrange these different substances, as 
shown by this analysis, in chemical order, it is evident that, 
for the expression of a simple formula, there is an excess of 
silicic acid present. But as the analysis shows an excess of 
2°74 per cent., it may possibly arise in the determination of 
the silicic acid, particularly as the mineral examined was not 
as pure as could-be wished; under these circumstances the 
following formula would represent the composition— 
Si, Al + 6 Mg H, 
which upon calculation gives— 
Ea Nt a ag Th | 
A Seas So. ee 8598 
6 Mg = 155010 ..... 38°53 
BEL Gis UO see 16°78 
4022°38 100° 
M. R. F. Marchand adds in a note to the above paper, 
that Dr. Giwartowski from Moscow had analysed the same 
steatite and found it composed of as follows :— 
Magnesia ....-+-+-++ee- 37°9 
SiCi@ ACIC. .. +... sols) We SOT, 
PAM TUTTUi ee fe oes o's” She eee ite 13'2 
Peroxide of iron ......- 3°1 
WW thie tics ose nk pipiens 
