BULLETIN OF THE BUSSEY INSTITUTION. 217 
only 65 grains of sulphate and 10 grains of carbonate of lime. 
Coquard * found 84% of carbonate of lime in the upper parts of min- 
eral gypsum at Aix. As a general rule, gypsum effervesces somewhat, 
when treated with acid, in those parts that have been exposed to the 
atmosphere. 
There is an old experiment of Spatzier f which deserves special 
mention in this connection, since it was made in an agricultural way, 
and for agricultural purposes. 
Spatzier selected a quantity of mould that had resulted from the 
rotting of vegetable matters, and made therewith a small garden bed, 
which he dressed with a moderate dose of fresh horse-dung and then 
dug over, in order to thoroughly mix the dung and earth, and to leave 
the soil loose and mellow. A few peas and beans were sown in the 
bed, and the entire surface of the soil was covered, to the depth of 
about a line, with finely powdered gypsum. A portable roof was 
arranged, so that the bed could be protected from heavy rains, and in 
dry weather the bed was carefully moistened by sprinkling it from a 
watering pot. At the end of three weeks, the gypsum was submitted 
to analysis, and it was found that the larger part of it had been changed 
to carbonate of lime. ‘The earth of the bed, also, was charged with the 
carbonate to the depth of half a foot, as was shown by its effervescing 
strongly when treated with an acid, although, at the beginning of the 
experiment, no trace of a carbonate could be detected, either in the 
earth of the bed or in the gypsum that was put upon it. On leaching 
some of the earth with cold water, Spatzier found “a not insignificant 
quantity of sulphate of ammonia,” whence he concluded that the 
gypsum had been decomposed by carbonate of ammonia, produced by 
the fermentation of the dung. It is not impossible that, in this special 
experiment, some small part of the decomposition may have been due 
toa reaction of this kind; but it is not at all likely that the decompo- 
sition was wholly or even chiefly due to this cause. There is every 
reason to believe that the deoxidizing action of the rich soil must have 
led to the reduction of some of the gypsum, and to the formation of 
sulphide of calcium, which was decomposed in due course by the acid 
carbonate of lime of the soil. 
* “ Bischof’s “ Elements of Chemical and Physical Geology,” London, 1854, 
1. 420. 
+ Erdmann’s “ Journal fiir tech. und ek. Chemie,” 1831, 11. 89. 
