Methods of Control 365 



phate and of lime may be ready for instant use. A 

 stock solution of blue stone may be prepared as 

 follows: Forty gallons of water are put into a 

 fifty-gallon barrel; forty pounds of blue stone are 

 placed in a basket and hung up so that the basket is 

 half covered by the water in the barrel. As the blue 

 stone is dissolved, each gallon of the water contains 

 one pound of the chemical. In another barrel may 

 be slaked forty pounds of fresh lime. Each gallon of 

 that will contain one pound of lime. By keeping the 

 slaked lime in the barrel covered with water and pre- 

 venting it from evaporating, and also keeping the 

 barrel with the blue stone solution covered to prevent 

 evaporation, we shall have stock solutions ready for 

 instant use. To make a 4-4-50 Bordeaux from stock 

 solutions, for instance, it. is necessary to take four 

 gallons from the stock solution barrel with blue 

 stone, and add this to twenty-one gallons of water. 

 Four gallons are also taken from the stock solution 

 barrel of slaked lime and added to twenty-one gal- 

 lons of water. The two solutions of twenty-five 

 gallons each are now added together, thus making a 

 4-4-50 Bordeaux. In this way it is easy to prepare 

 any formula from the stock solutions. To determine 

 if the Bordeaux contains sufficient lime, the following 

 test may be carried out. A few drops of potassium 

 ferrocyanide are added to the Bordeaux mixture. 

 If sufficient lime is present, no change will take place, 

 but if the mixture is deficient in lime, a dark reddish 

 brown color will appear where the drop strikes the 

 liquid. This testing fluid is easily prepared by dis- 



