323 
Sulphat of JLimec 
No. 8. Buller's . Appearance like No. 7, only the facets of the 
jchrystals much smaller. Silex 1, alumina 0, carbonat of mag- 
nesia 14, the rest limestone. 
No. 9. Baker's. Colour ash-grey intermixed with brown mica, 
so as to bear the appearance of a mixture of pepper and salt : 
Small lustry chrystais. I obtained silex 36, undccomposed mica 
4, alumina by precipitation 6, carbonat of magnesia 4. The rest 
I limestone. 
Hence it should seem, that the proportion of magnesia in these 
stones, is not so great as to produce any remarkable effect, either 
in agriculture, or as cements. The last (No. 9,) is doubtless the worst, 
as containing so large a proportion of siliceous sand, which on 
light soils is worse than useless. 
Tenant’s limestones, contained a much larger portion of magne- 
sia, and the effect was therefore more evident. The greater pror 
portion of limestone used in England than in this country, with the 
same effect, may arise not from the nature of the lime, but of 
the soil whereon it is put. It is there used in large proportion to 
strong loamy arable soils, and to swampy, spouty ground, that tends 
to produce sorrel. When it is used for the purpose of producing 
white clover, for which it seems to be a specific stimulus, it is not 
applied in greater proportion there than here, and merely as a top 
dressing. That is, so far as my observation and recollection ena- 
bles me to speak on the subject. T. C, 
On Sulphat of Lime , Plaister of Paris , or Gypsum , and the methods 
of ascertaining it. 
There are two natural varieties of sulphat of lime, the common 
or hydrous ; and the anhydrous containing no water of chrystalli- 
zation. 
The common plaister of Paris is made anhydrous by boiling from 
4 to 6 hours in an iron pot : and it becomes a cement , by re-absorb- 
ing its water of chrystallization. 
Common sulphat of lime, may be made anhydrous, by exposing 
it in a crucible in small quantities to a full red heat for an hour. 
The carbonic acid in common limestone may be regarded as 
44J per cent. 
