160 GAS LIME COPPEE SULPHATE 



C0 2 + 2CaS + 3O = CaS 2 O 3 + CaC0 3 . 



Calcium thiosulphate. 

 CaS0 3 + O = CaSO 4 . 

 CaS 2 3 + 2O 2 + CaH 2 O 2 = 2CaSO 4 + H,O. 



The composition of fresh gas lime (from London gasworks) is, 

 according to Guyard l : 



100-00 



If the unoxidised sulphur compounds remain in gas lime until its 

 application to the land, great harm and sometimes total destruction of 

 vegetation may ensue. In view, then, of the uncertainty of its action, 

 its general use cannot be recommended. 



Copper Sulphate. Though this substance cannot act as a direct 

 plant food and has seldom (or perhaps never) been used as a manure, 

 some results obtained when spraying crops for disease or for the pur- 

 pose of destroying charlock, etc., seem to indicate that it acts as a 

 powerful stimulus to the growth of certain plants, for in many cases 

 distinctly beneficial effects have been observed from its use in the case 

 of grain crops and potatoes, where no charlock or disease was present. 



Catalytic Manures. Under this name Bertrand' 2 proposes to- 

 include certain substances, which, though, so far as is known, not 

 capable of directly supplying food to the plant, have been found to- 

 act favourably upon many crops. The best example is perhaps man- 

 ganese salts, to which reference has already been made (p. 14). Zinc 

 compounds have been found to act favourably on the growth of mush- 

 rooms ; boron, iodine, fluorine and bromine compounds have also been 

 found to have beneficial effects upon the yield of certain crops. But 

 the costliness of most of these compounds is against their general use 

 for manurial purposes. 



724. 



l. Soc. Chim. xxv. 103; Jour. Chem. Soc., 1876, 123. 

 2 Seventh Inter. Congr. App. Chem., London, 1909, Jour. Soc. Chem. Ind., 1909, 



