DISEASES OF THE POTATO. 167 



is to dip a strip of blue litmus paper in the solution. If it 

 turns red add more lime. If it remains blue the solution 

 is safe to use. 



COPPER AND SODA MIXTURE FOR SPRAYING. This mixture, 

 as recommended by the Irish Board of Agriculture, con- 

 sists of 21bs. of sulphate of copper of 98 per cent, purity ; 

 2|lbs. of pure washing soda; and 10 gallons of clean water. 

 If a large quantity be desired, use 81bs. of sulphate of 

 copper; lOlbs. of washing soda; and 40 gallons of water. 

 To make the 10-gallon mixture dissolve the sulphate of 

 copper in 1 gallon of water, and the soda in another 

 gallon of water, then add the two to 8 gallons of water. 



POTATO TOBFR INFECTED WITH BLACK SCAB OR W/.RT DISEASE. 

 (See p. 170.) 



For the larger quantity place the copper in a canvas bag 

 and steep it in 35 gallons of water till dissolved, 

 then dissolve the soda in 5 gallons of water, and mix the 

 two together. Add the soda solution slowly to the copper 

 mixture, and stir continuously. To ascertain if the mix- 

 ture is of the right strength test it with blue litmus paper. 

 If the paper turns red, add more washing soda till, with 

 further tests with the litmus paper, the latter remains 

 blue. The vessels used for the solution should be of wood, 

 and not of metal. Drain the solution through canvas be- 



