MISCELLANEOUS 21 7 



The grain is dressed with this liquid about twenty- four hours 

 before sowing. The spores of the fungi which may be on the 

 grain are thus destroyed, and the thin film of sohible copper 

 sulphate which remains on the wheat is converted, probably 

 mainly by the calcium carbonate of the soil, into insoluble 

 compounds soon after sowing, and before the wheat germinates. 

 If this conversion of the copper into insoluble compounds did 

 not occur the wheat would probably be killed by the treat- 

 ment. In America the grain is soaked for twelve hours in a 

 solution of 1 lb. of copper sulphate in 24 gallons of water, and 

 then for five minutes in lime-water. 



Copper sulphate is also employed for spraying the foliage of 

 plants for the prevention of fungoid diseases. For this purpose 

 a solution not stronger than 1 lb. of the salt in 20 gallons of 

 water should be used, or the leaves will be injured. 



Copper sulphate has also been used for the destruction of 

 certain cruciferous weeds, especially charlock. If barley or 

 oats are badly infested with this plant it is found that if the 

 whole field be sprayed with a 2 or 3 per cent, solution of 

 sulphate of copper, using about 40 gallons to the acre, provided 

 the charlock plants are not above two or three inches high, 

 their leaves blacken, and they die, while the oats, barley, or 

 clover are not injured. 



It is difficult to explain why the charlock should be killed, 

 while the cereal is uninjured, but it may be due to plasmolysis 

 (see chap, v., p. 78) occurring more readily in the one case 

 than in the other. But copper sulphate is too corrosive in its 

 effect on foliage to be very suitable as a fungicide for many 

 plants, and a much more generally used substance is copper 

 hydroxide, CulJ.fi.,, or really basic copper sulphate, i.e., a com- 

 pound of 4 or 5 molecules of copper hydroxide with one of 

 copper sulphate, applied in suspension in water. 



This is largely used under the name of Bordeaux mixture, 

 and is made as required by the action of slaked lime upon 

 sulphate of copper : 



