Prof. Gray on the Botany of Japan. 187 
maghesia, sparingly soluble in cold dilute acetic acid. This com- 
bination takes place between 180° and 200° C., at which — 
atures the magnesian carbonate tends to pass into the still less 
soluble state of magnesite, in which, as we have shown, it no 
longer shows any disposition to unite with carbonate of lime. 
Hence it happens that in all our experiments a ion of magne- 
site is mingled with the dolomite, and cannot be completely sepa- 
rated from it. Dilute acids slowly attack both, but unequally, so 
that we finally obtain a residue which contains carbonate of 
magnesia free from lime: but the solution having taken up a 
portion of magnesite, contains more magnesia than is required to 
form a dolomite with the carbonate of lime; so that we have 
from 53-0 to 60:0 p. ¢. of magnesian carbonate instead of 45-0 as 
in pure dolomite. In nature the combination of the two carbon- 
ates has doubtless taken place slowly, and necessarily at the 
lowest temperature, which is probably much below 130° €., so 
that we may suppose that it is only in the absence of a sufficient 
- quantity of carbonate of lime that a portion of the magnesian 
_ ¢arbonate has been converted into magnesite. 
(To be concluded in the next No.) 
Art. XX.—Eextract from the concluding part of a Memoir on the 
Botany of Japan, in its Relations to that of North America, and 
of other parts of the Northern Temperate Zone; by ASA GRay.* 
orth America, 134; in Baiegeaa ae 
the 580 Japanese entries, there are os stemigiee 
pean representatives, a little above 8.48 per cent of identical species, 0. 
estern N. Ameri, 2 righ ge" S oe «090 
Eastern American representati sae SS age 4 
law ‘xtracted from the Memoirs of the American Academy of Arts and Sciences, 
Series, yol, yi, 
