366 MISCELLANEOUS PRODUCTS USED IN AGRICULTURE. XVI. 



spirostylis has been found to contain as much as O05% of 

 copper, and its presence in any district is regarded as an indi- 

 cation of copper in the soil.* Large quantities of copper salts, 

 however, especially if they be present as sulphide, in which 

 case, by oxidation, soluble sulphate is probably slowly formed, 

 appear to be injurious. The author found, in a soil in which 

 fruit trees refused to grow, about 0'2 % of copper oxide, 

 probably derived from pyrites. 



Copper salts find their chief use in agriculture as fungicides. 

 The most important commercial salt is the sulphate, occurring 

 crystallized as "blue vitriol," CuS0 4 .5H. 2 O. This substance 

 which was formerly often adulterated, especially for agricul- 

 tural purposes, with the much cheaper ferrous sulphate, with 

 which it is isomorphous is now very largely used, and the 

 modern product is, as a rule, fairly pure. 



The pure salt has a specific gravity of 2*28 and a solubility 

 in 100 parts of water which varies from 31'6 at to 203 '3 at 

 100. At 10 100 parts of water dissolve about 37 parts, at 

 20 about 42-3 parts of the crystallized salt. 



A solution containing 2% of CuS0 4 .5H. 2 has a specific 

 gravity of 1-0126, a 4% solution 1-0254, and a 6% solution 

 1-0384. Copper sulphate is insoluble in absolute alcohol, 

 though very slightly soluble in aqueous alcohol ; it is much 

 more soluble in glycerine. 



Copper sulphate has long been used for dressing seed wheat, 

 with a view to the prevention of such fungoid diseases as smut, 

 rust, and bunt. For this purpose each quarter of corn receives 

 2 gallons of water in which about 2H). of copper sulphate 

 crystals have been dissolved. The dressing is usually applied 

 about 24 hours before sowing and the grain is thoroughly 

 mixed and incorporated with the solution. Each grain of 

 wheat becomes coated with the liquid, which on evapora- 

 tion leaves a thin film of the salt. The spores of the fungi are 

 thus destroyed, but the copper is converted into insoluble 

 compounds soon after the seed is sown and before germination 

 of the wheat embryo commences. The corn, therefore, is not 

 injured, though it would probably be killed outright if it were 

 not for the action of the constituents of the soil (probably 



* Heckel, J.C.S. 1901, abst. ii. 331. 



