266 



MATERIALS OF INDIRECT VALUE 



[chap. 



that gas lime should be applied to the land unless the 

 ground is badly infested with some insect pest which 

 the raw sulphur compounds may check or destroy, and 

 even then on light soils the fertility of the land may be 

 impaired for some time. It is on heavy land that gas 

 lime is of most value ; the flocculating effect of the 

 calcium salts improves the texture, and the soil also 

 contains a great reserve of dormant potash compounds 

 to be rendered soluble. The crude material from the 

 gas works should be laid up in heaps, mixed with a 

 little earth for a year or more, spread on the stubbles in 

 the early autumn, and then ploughed in. 



Tahi.e LXXXIII. — Analyses ok Gas Lime. 



Gypsum. — That gypsum, crystallised sulphate of 

 lime, or land plaster, CaS04, 2H0O, had a beneficial 

 effect upon certain crops and soils has been known for 

 a very long time ; it was probably familiar to the 

 Romans, and the knowledge survived to a certain 

 degree among the southern nations, especially in con- 

 nection with vines. In Britain it appears to have been 

 less commonly used and no very general agreement as 

 to its value had become traditional ; in fact it was only 

 among the hop growers of Kent and especially of Sussex, 



