60 T. 8. Hunt on Lime and Magnesia Saits. 
sia retains a portion of carbonate of magnesia even after the so- 
lution has been long boiled, or evaporated to dryness; this is 
manifested by an alkaline reaction and by the power of precipi- 
tating the nitrates of silver and copper. That these reactions 
are due to dissolved carbonate, and not to a sulphate with excess 
of base, is indicated from the fact that the addition of small 
quantities of hydrate of soda to a solution of sulphate of mag- 
nesia gives rise to a precipitate of hydrate of magnesia which 1s 
insoluble in the sulphate, and does not communicate to it an 
alkaline reaction, 
On the supposed decomposition of gypsum by dolomite, 
§96. Haidinger, according to Bischof, has endeavored to ex- 
plain the origin of the sulphate of magnesia observed in many 
gypsum quarries by supposing a decomposition of the sulphate 
of lime by dolomite, and Suckow has also proposed the same 
explanation to account for an efflorescence of Epsom salt near 
Jena (Chem. Geology, i, 430, iii, 159). Bischof mentions in 
connection with the latter instance an observation of Mitscher- 
lich, which from the omission of a few words in the English 
translation, seems to imply that this chemist had observed the 
complete decomposition of bitter-spar by a solution of gypsum. 
On reference to the German edition, however, it appears that Mit- 
scherlich had observed the decomposition of carbonate of mag- 
nesia by gypsum, and thus that his experiments do not confirm 
the hypothesis of Haidinger and Suckow, which we have here 
to examine. It is therefore by an error that in my recent essay 
on Natural Waters, § 19-21, I have attributed the views of 
these geologists to Mitscherlich, whose original memoir cited by 
Bischof is not accessible to me. 
$97. In the paper just cited I have recorded the following 
experiments: A solution of gypsum was made to percolate 
slowly through a column of several inches of finely powdered 
dolomite previously washed with pure water. After ten suc- 
cessive filtrations of the liquid, occupying as many days, no per- 
ceptible amount of sulphate of magnesia was formed. Solutions 
of gypsum, and others of chlorid of calcium, were then digested 
for several months at the ordinary temperature with pulverized 
dolomite, and also with native crystalline carbonate of magnesia 
(from Styria), with similar negative results. Solutions of gyp- 
sum impregnated with carbonic acid were also allowed to remain 
in contact with pulverized dolomite and magnesite during the 
warm season for a period of six months, and even then only 
traces of magnesia were taken into solution. 
In one experiment out of many, 10-0 gr. of pure crystalline 
dolomite from Galt ($82) and 1-0 gr. of pure crystalline gypsum 
°-18° C, for six 
were digested with 200 c.c. of water at from 15°-18 
