m 
In burning lime there are some particular pre- 
cautions required for the different kinds of lime- 
stones. In general, one bushel of coal is sufficient 
to make four or five bushels of lime. The mag- 
nesian limestone requires less fuel than the common 
limestone. In all cases in which a limestone con- 
taining much aluminous or siliceous earth is burnt, 
great care should be taken to prevent the fire from 
becoming too intense ; for such lime easily vitri- 
fies, in consequence of the affinity of lime for 
silica and alumina. And as in some places there 
are no other limestones than such as contain other 
earths, it is important to attend to this circumstance. 
A moderately good lime may be made at a low red 
heat ; but it will melt into a glass at a white heat 
In limekilns for burning such lime, there should be 
always a damper. 
In genera], when limestones are not magnesian, 
their purity will be indicated by their loss of weight 
in burning ; the more they lose, the larger is the 
quantity of calcareous matter they contain. The 
magnesian limestones contain more carbonic acid 
than the common limestones ; and I have found all 
of them lose more than half their weight by calcin- 
ation. 
Besides being used in the forms of lime and car- 
bonate of lime, calcareous matter is applied for the 
purposes of agriculture in other combinations. 
One of these bodies is gypsum or sulphate of lime. 
This substance consists of sulphuric acid (the same 
body that exists combined with water in oil of 
vitriol) and lime ; and when dry it is composed of 
55 parts of lime and ^5 parts of sulphuric acid. 
