New York Agricultural Experiment Station. 327 



a stock solution of copper sulphate. A saturated solution, in which 

 the water contains all of the copper sulphate which it will take up, 

 holds about 3 pounds of the copper sulphate to the gallon (49 ozs. 

 at 59° F.). For a 5 lb. formula i^ gallons of such solution would 

 be taken. 



Some hold that it is more convenient to make a stock solution which 

 contains 2 lbs. per gallon. Such a solution gradually becomes stronger 

 as evaporation takes place, whereas the saturated solution is always 

 as strong as it can be made. 



To dissolve copper sulphate in large quantities in cold water, hang 

 the sulphate in a coarse sack in the top of the water. Leave for a 

 day or more if necessary. 



Stock lime paste. — Several ways are known whereby the bordeaux 

 mixture may be tested to find out whether enough lime has been 

 added to unite with all of the copper sulphate, thus avoiding the 

 necessity for weighing the lime. This permits of the slaking of con- 

 siderable quantities of lime at one time. The lime may then be kept 

 in excellent condition for some time if covered with water to exclude 

 the air. 



Ferrocyanide of potassium test. — The test most commonly used for 

 determining whether or not enough lime has been put into the 

 bordeaux mixture to combine with all of the copper sulphate is the 

 ferrocyanide of potassium test, commonly called the " ferrocyanide " 

 test. 



Potassium ferrocyanide is also called yellow prussiate of potash. 

 It is a very poisonous yellow salt which dissolves readily in water. 

 A few cents' worth dissolved in about ten times its bulk of water will 

 ordinarily last through the season. In using this test fill the spray 

 tank half to two-thirds full of the copper sulphate solution, then pour 

 in the milk and lime. Stir the mixture thoroughly and add a drop 

 of the potassium ferrocyanide. If enough lime has been added the 

 drop will not change color when it strikes the mixture, otherwise it 



