IX.] VARIETIES OF LIME 251 



Derbyshire and North Yorkshire, or argillaceous in the 

 Lias] as chalk, and even as shell sand, on the Cornish 

 and other coasts. The so-called " burning " consists in 

 driving off by heat the carbonic acid contained in the 

 calcium carbonate. The resulting lime, known some- 

 times as quicklime, stone lime, cob lime, lime shells, 

 etc., combines with great readiness with water, developing 

 much heat and falling down into a fine powder termed 

 " slaked lime," and this slaked lime will then combine 

 with the carbonic acid present in the atmosphere to 

 reconstruct the original carbonate of lime. Thus when 

 lime is applied to the soil it very rapidly becomes 

 carbonate and the effects of " liming " are really due to 

 carbonate of lime. 



The quality of lime varies considerably, according 

 as it has been made from a pure limestone or from the 

 impure forms containing some admixture of clay and 

 sand. In the former case the result is a white, " fat," 

 lime which swells considerably on slaking and falls 

 into a very fine powder ; the other grey or thin limes 

 do not slake so readily nor swell much, they also 

 contain a smaller proportion of free lime and are less 

 valuable for agricultural purposes. In some parts of 

 the country the limestone is dolomitic and contains 

 considerable proportions of magnesium carbonate, but 

 the limes arising from it are not regarded with so much 

 favour by farmers. 



Lime ashes, which are to be had cheaply in the 

 neighbourhood of the kilns, consist of the waste 

 accumulating in burning the lime and are therefore 

 mixtures of lime in a powder with the ashes of the 

 coal employed. The percentage of lime may vary from 

 20 to 60 according to circumstances, so that the value 

 of each lot must be judged by its apparent cleanliness 

 and freedom from clinker. 



