126 THE PRACTICAL SIDE OF 



Lime sold by builders often sets when it is 

 mixed with water, and is, in consequence, of 

 little use, while lime obtained from the purer 

 carbonates is much more easily slaked and 

 pulverises very readily, so that it can be 

 thoroughly distributed on the land in the form 

 of an almost impalpable powder. The best 

 classes of limestone vary in their contents of 

 calcium carbonate from 94 to 98 per cent., 

 while a sample of Silurian limestone con- 

 tained only 44 per cent. There should 

 be as great discrimination in employ- 

 ing lime as in using marl, which varies 

 enormously in its content of carbonate of 

 lime. Where chalk is used instead of lime, 

 it should be spread before a frost — all the 

 better if it is in a wet or moist condition — 

 that it may pulverise when the thaw arrives. 

 Chalk, as we have seen, is chiefly carbonate, 

 a condition to which lime returns on exposure 

 to the air. When chalk is burnt in the kiln 

 it becomes oxide of calcium or quicklime, 

 possessing caustic properties, but when mixed 

 with water it slakes and becomes hydrate 

 of lime, and is then fit for spreading on the 

 land. In the past, and occasionally at the 

 present time, farmers deposited quicklime in 

 heaps on their ploughed land and allowed 



