SPECIAL SOIL IMPROVERS 



Nitrification will, therefore, proceed either above or below 

 a lump of lime material, but it is much better to get a small 

 dressing well distributed than to depend upon haphazard 

 heavy dressing. The lime, as soon as it is applied to the 

 soil, combines with water and forms calcium hydrate, and then 

 absorbs carbonic acid, forming calcium carbonate. Lime 

 also enters into combination, at any rate in a temporary 

 manner, with the organic matter and clay. The addition 

 of lime to a soil increases the amount of available potash 

 and available nitrogen. It does not increase the amount 

 of available phosphorus, excepting in the case of soils 

 containing much organic matter, where a considerable 

 fraction of the total amount of phosphorus in the soil is 

 in some form of organic combination. Lime, when turned 

 into calcium bi-carbonate, coagulates clay, and opens up 

 nearly all types of soil. It is, therefore, particularly suitable 

 for the heavier types of land. As it tends to dry out clay 

 soils, lime should be applied fairly early, otherwise the soil 

 may be too dr}^ for satisfactory germination of the seeds. 

 Lrime is especially necessary with high farming. Super- 

 phosphates, sulphate of ammonia, nitrate of soda,kainit, farm- 

 yard manure and organic nitrogen manures all demand hme 

 in the soil. There are a great many forms of industrial waste 

 lime which can be used, the relative values of which depend 

 upon the amount of calcium contained. When limestone is 

 burned it loses about 40 per cent, of its weight, and the subse- 

 quent cost of carriage is that much less. It may be cheaper 

 to burn coal in the lime kiln, and thus to reduce the weight, 

 than to burn coal in a steam engine for the purpose of carrying 

 useless carbonic acid. These varied forms of calcium car- 

 bonate can only be considered ii they are relatively cheap. 

 Very considerable quantities of waste lime are produced in 

 the '^Leblanc " soda process. Calcium sulphide obtained as 

 a by-product is treated with carbon dioxide in water with 

 the evolution of hydrogen sulphide, then used for manufacture 

 of sulphur. The waste calcium carbonate is run into heaps 

 and allowed to dry spontaneously. This material, often 

 called " Chance " mud, or lime mud, has proved a perfect 



