DISEASES 179 



water. In another cask containing 50 gallons of water 

 suspend 5 pounds of copper sulphate (blue vitriol) in a 



Fig. 98. Potatoes sprayed for prevention of blight on right. Potatoes not sprayed 



on left. 



gunny sack and place just beneath the surface until dis- 

 solved. When well dissolved the lime and the copper sul- 

 phate solutions should be mixed. This is best done if the 

 solutions are taken in pailfuls from each cask alternately 

 and put into a third. It is well to test the solution to 

 determine its effect upon the leaves of the plants. This 

 can be done by putting a bright knife blade into the 

 solution. If the blade remains bright the solution will not 

 injure the plants, but if the blade takes on a coppery hue 

 more lime should be added. The lime prevents the copper 

 sulphate solution from injuring the plants. It should then 

 be put into a spraying machine and sprayed on the plants 

 in the form of a fine mist. It requires about fifty gallons of 



