oo cap pam ah Rg ae ae ca oa eo Niel nel al ee a alae Dea a 
T. 8. Hunt on Lime and Magnesia Salts. ; 63 
contained but a trace of magnesia in solution. To the residue 
was added 250 c.c. of a solution of gypsum partially saturated 
with carbonic acid. After twenty-four hours digestion 200 ¢.c. 
of the liquid were found to yield on evaporation little gypsum, 
but an amount of sulphate of magnesia equal to 0330 gr. of 
carbonate. A second portion of gypsum solution with carbonic 
acid being added gave, after frequent agitation for seven days, a 
quantity equal to not less than 8°93 gr. of sulphate of magnesia 
to the liter, showing that a considerable portion of gypsum be- 
sides that first in solution took part in the reaction. In — as 
in all the previous experiments, a coarsely crystalline and very 
pure gypsum, preroney pulverized and washed with distilled 
water, was mad of, 
§ 101. From al these eoaneneate it appears that although 
quantities in some magnesian limestones. It also appears that, 
with the intervention of carbonic acid, hydrate of magnesia, 
and rocks like predazzite containing this substance, may decom- 
be repre- 
sented as a compound of monocarbonate and ool of magne- 
sia, is probably resolved by a solution of gypsum into carbonate 
of lime and hydrate of magnesia, a mixture like predazzite, 
which requires, as in § 99, the intervention of carbonic acid to 
oa it to decompose a further portion of gypsum 
Production of dolomite. 
§ 102. In $80 I have already discussed the conditions under 
which ioe anhydrous double carbonate of lime and magnesia 
may be formed, and referred to the sacperimeiie in a previous 
paper in which ‘T had succeeded in producing it at temperatures 
considerably above 100° C. It was with a hope of obtaining it 
at lower temperatures that many of the experiments already 
detailed in this paper were undertaken. Thus it was not im 
sible that from the supersaturated solutions holding both the 
mouocarbonate of lime and that of magnesia, a compound of 
the two might be deposited. The experiments alread y described, 
however, show that the carbonate of lime separates completely 
after a time as a hydrate, without any trace of carbonate of 
magnesia. Again it was hoped that the slow union of the two 
carbonates at temperatures below 100° C. might give rise to the 
anhydrous double salt, instead of which, however, we have seen 
that there are formed the hydrated double carbonates already 
escribed. Attempts were el made to dehydrate these com- 
pounds and thus produce dolomite, but with partial success. 
