392 REPORT OF THE CHEMIST OF THE 
SULPHATE OF LIME. 
This material is known in chemistry as calcium sulphate; 
its common names are land-plaster and gypsum. It is a com- 
pound of calcium and sulphuric acid. It possesses value on 
the farm because it is an excellent absorbent and also because 
it may undergo chemical changes in the soil as a result of 
which insoluble potash compounds are made soluble. In dis- 
solving rock phosphates (phosphate of calcium) with sulphuric 
acid, a considerable amount of calcium sulphate is formed. 
Commercial acid phosphates, therefore, contain more or less 
sulphate of lime. 
WOOD ASHES. 
Wood-ashes vary greatly in composition. When of good 
quality, they should contain not less than 35 per ct. of calcium 
oxid, 8 per ct. of magnesium oxid and 5 per ct. of potash. 
These compounds are present largely in the form of carbonates. 
COMPARATIVE COMPOSITION OF LIME COMPOUNDS. 
It is a matter of interest and importance to compare the 
principal lime compounds with reference to the amount of 
calcium oxid contained in them. This is shown in the follow- 
ing arrangement: 
Lime Water Carbon dioxid 
FORM OF LIME COMPOUND. (CaO) (H»O) COs 
Per ct. (Per ct. Per ct. 
Calcium oxid Clime) ee seen eae ee ae 100 


Calcium hydroxid (slaked lime)...... la. (ie We 24.3 — 
Calcium carbonate (carbonate of lime).... 56 — 44 
It is seen that 100 pounds of pure lime (CaO) contains 100 
pounds of calcium oxid; that 100 pounds of pure slaked lime 
(calcium hydroxid) contains an amount of calcium equiva- 
lent to about 76 pounds of calcium oxid; and that 100 pounds 
of carbonate of lime contains an amount of calcium equiva- 
lent to 56 pounds of calcium oxid. This means that one pound 
