COPPER SALTS AS FUNGICIDES 



Other hypochlorites have heen used, and a process known as the 

 "Hermite" process, by which sea-water is electrolysed and the fluid 

 so obtained used for disinfecting sewage, etc., depends for its action 

 upon the production, during electrolysis, of hypochlorites, probably 

 chiefly of magnesium. 1 



Copper Salts. Soluble copper salts are extremely poisonous to 

 plants. In water cultures it was found that the presence of 0*0055 

 part of copper sulphate in 100 parts of water was sufficient to kill 

 young; wheat plants ; while 0-0049 of the bromide, 0-0050 of the 

 chloride, or 0*0061 of the nitrate produced a similar effect.' 2 On the 

 other hand, insoluble copper compounds not only appear to be non- 

 poisonous but are often taken up by the plant. Haricot beans grew 

 even better in nutrient solutions to which copper oxide had been 

 added. 3 Copper is said to be often present in plants to the extent of 

 0*003 per cent, even on ordinary soils, while as much as 0*056 per 

 cent may be present iti the dry matter of plants growing on soils con- 

 taining much copper. 4 In Australia a plant Polycarpaa spirostylis 

 has been found to contain as much as 0*05 per cent of copper, and 

 its presence in any district is regarded as an indication of copper in 

 the soil. 5 Large quantities of copper salts, however, appear to 

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

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

 author found, in a soil in which fruit trees refused to grow, about 0*2 

 per cent 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 crystallised 

 as "blue vitriol," CuSO 4 .5H 2 O. This substance which was formerly 

 often adulterated, especially for agricultural 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 crystallised salt. 



A solution containing 2 per cent of CuSO 4 .5H 2 has a specific 

 gravity of rOl'26, a 4 per cent solution, 1*0254, and a 6 per cent 

 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 is moistened with 2 gallons 

 of water in waich about 2 Ib. of copper sulphate crystals have been 



1 See Roscoe and Lunt, Jour. So?. Chem. Ind., 1895, 224. 



'^Coupin. Compt. Rend., 1898, 400; Jour. Chem. Soc., 1899, Abstracts, ii. 118. 



3 Tschirch, Ann. Agron., 1895, 544 ; Jour. Chem. Soc., 1896, Abstracts, ii. 328. 



4 MacDougal, Exper. Stat. Record, 1899, 24 ; Jour. Chem. Soc., 1900, Abstract*, 

 ii. 235. 



5 Heckel, Jour. Chem. Soc., 1901, Abstracts, ii. 331. 



