^54 MATERIALS OF INDIRECT VALUE [chap. 



benefited by liming, and when the percentage falls 

 to \ per cent, lime becomes a necessity to enable the 

 manures to exert their proper action. 



Many clays and sands are in this latter condition ; 

 and although the absence of lime may often be con- 

 cluded from the appearance of the vegetation, every 

 farmer ought to get a determination made of the 

 amount of carbonate of lime in his soil, because the 

 whole scheme of manuring should depend on whether 

 the soil is properly supplied with a base. 



In arable land the presence of the small sorrel 

 {Rumex acetosella), corn marigold {Chrysanthemtini 

 segetuni), Spurrey {Spergula arvensis)^ and the growth 

 of foxglove {Digitalis purpurea) and bracken {Pteris 

 aquilind) on the waste places are pretty sure signs of 

 the absence of lime, while the pastures on such soils are 

 generally very deficient in leguminous herbage. If a 

 little soil when covered with dilute hydrochloric acid 

 shows no visible effervescence, the proportion of 

 carbonate of lime must be below what is desirable for 

 the healthy growth of vegetation. Nor must it be 

 supposed that the use of artificial manures, such as 

 superphosphate of lime, or bones which are phosphate 

 of lime, or gypsum which is sulphate of lime, will 

 obviate the necessity of liming. Lime or its carbonate 

 are needed in the soil to supply a free base, and in 

 the compounds mentioned it is already saturated with a 

 fixed acid ; in fact, in superphosphate of lime there is an 

 excess of acid, so that this fertiliser reduces the amount 

 of carbonate of lime in the soil. Gas lime is again of 

 very little service in this connection, since the base has 

 already been largely combined with various compounds 

 of sulphur, and still remains so after these sulphur 

 compounds have been oxidised by exposure of the gas 

 lime for some time. The following table (LXXVIII.) 



