New York AGRICULTURAL EXPERIMENT STATION. 391 
taining larger amounts of impurities. Magnesian stone-limes 
slake imperfectly. 
One bushel of stone-lime of good quality, on slaking, in- 
creases in bulk to two or three bushels of slaked lime. The 
weight per bushel decreases roughly about one-half, for ex- 
ample, from 90 to 45 pounds. The bulk and weight of slaked 
lime depend upon the composition of the quicklime used, upon 
the amount of water added, and upon some special conditions 
of the slaking process. 
The calcium hydroxid of slaked lime easily absorbs carbon 
dioxid gas from the air and changes gradually into calcium 
carbonate. Just as quicklime is impure calcium oxid, so 
slaked lime is impure calcium hydroxid. Ordinary slaked lime 
is, therefore a mixture of calcium hydroxid and calcium car- 
bonate with such impurities as may have been present in the 
lime before slaking. 
The slaking of lime also takes place when lime is exposed to 
the air, this process being known as air-slaking. When lumps 
of stone-lime stand exposed for some time, the outer layer 
gradually absorbs moisture from the air and goes through the 
process of slaking and forming a fine powder. In the air- 
slaking process, more or less calcium carbonate is also formed. 
Hence, air-slaked lime usually contains larger amounts of car- 
bonate and less of hydroxid than water-slaked lime. The 
rapidity with which limes air-slake depends upon different 
conditions. Dry, fine air-slaked lime may contain as much as 
75 per ct. of calcium oxid. 
CARBONATE OF LIME. 
Carbonate of lime is chemically known as calcium carbonate. 
In this form calcium oxid (CaO) is combined with carbon 
dioxid (CO,), thus forming calcium carbonate (CaCQ,). 
Limestones of high grade and marbles consist largely of cal- 
cium carbonate. It forms varying proportions of shells, marl, 
etc. As previously stated, it is present in variable amounts in 
slaked lime. 
