2S6 
and its taste : it regains its power of effervescing, 
and becomes the same chemical substance as chalk 
or limestone. 
V ery few limestones or chalks consist entirely of 
lime and carbonic acid. The statuary marbles, or 
certain of the rhomboidal spars, are almost the only 
pure species ; and the different properties of lime- 
stones, both as manures and cements, depend upon 
the nature of the ingredients mixed in the lime- 
stone ; for the true calcareous element, the car- 
bonate of lime, is uniformly the same in nature, 
properties, and effects, and consists of one propor- 
tion of carbonic acid 41*1, and one of lime 55 . 
When a limestone does not copiously effervesce 
in acids, and is sufficiently hard to scratch glass, it 
contains siliceous, and probably aluminous earth. 
When it is deep brown or red, or strongly coloured 
of any of the shades of brown or yellow, it contains 
oxide of iron. When it is not sufficiently hard to 
scratch glass, but effervesces slowly, and makes 
the acid in which it effervesces milky, it contains 
magnesia. And when it is black and emits a foetid 
smell if rubbed, it contains coally or bituminous 
matter. 
The analysis of limestones is not a difficult mat- 
ter ; and the proportions of their constituent parts 
may be easily ascertained by the processes described 
in the Lecture on the Analysis of Soils; and usually 
with sufficient accuracy for all the purposes of the 
farmer, by the fifth process. 
Before any opinion can be formed of the manner 
in which the different ingredients in limestones 
modify their properties, it will be necessary to con- 
