130 THE POTATO 



Testing Bordeaux Mixture. In practice little 

 attention is paid to the quantity of lime, except that 

 sufficient is added to combine with all of the copper 

 sulphate. To determine when this has taken place 

 the potassium ferrocyanide test is made. Purchase 

 ten cents' worth of potassium ferrocyanide, or yellow 

 prussiate of potash, and dissolve it in water. Isabel 

 it ' * Poison. ' ' Stir the Bordeaux mixture in the spray- 

 tank and take out a sample in a small vessel, to which 

 add a drop of potassium ferrocyanide. If no change 

 in color is noted where it dropped there is sufficient 

 lime, but it is better to add lime solution equivalent to 

 a pound of lime more. If the drop changed the color 

 of the solution reddish brown it shows that there is 

 not enough lime. 



Strength of Solution. For potatoes, i pound 

 of copper sulphate to 7 or 8 gallons of water is com- 

 monly used; that is : 



Copper sulphate (blue vitriol), 6 pounds. 



Quicklime (not slaked), 4 to 6 pounds. 



Water, 48 to 50 gallons. 



Bordeaux Dust, 1 or Dry Bordeaux Mixture, 

 can be made in two ways : 



1 . Slaking the lime by pouring a strong solution of 

 copper sulphate over it. 



2. Mixing the strong copper sulphate solution with 

 freshly slaked lime which has been made into a paste, 

 then placing the mixture in a bag and drying and pul- 

 verizing it. The two ingredients must be well mixed 

 and passed through a fine sieve. Dry Bordeaux is 

 offered for sale under various names. Adler's Bor- 



1 For details, see Missouri Bui. 60. (N. Y.) Geneva Bui. 243, p. 325. 



