130 The Spraying of Plants. 



perienced in making the mixture can tell by its color when 

 sufficient lime has been added, but he cannot always tell how 

 much to add in excess of the amount demanded by the test. 

 For this reason it is safer to use a definite formula, provided 

 the materials are fairly pure, since then there is less chance of 

 a mistake ; this applies especially to beginners. 



Another test sometimes employed is to insert into the mix- 

 ture a polished iron surface. If an insufficient amount of lime 

 is present, so that some copper still remains in solution, the iron 

 will become coated with this metal. The test is said to be very 

 delicate. 



It is probably true that, as a rule, each extreme should be 

 avoided. The formulas at present in use in America may be 

 divided into two classes,^- those in which the ingredients are 

 weighed, and those in which the ferrocyanide of potassium test 

 is used. Among the former we have the following : 



The " Standard," or 3.6 per cent Bordeaux Mixture. 



Copper sulphate 6 pounds. 



Quicklime 4 " 



Water 22 gallons. 



This formula was at first extensively used, but it was found 

 that a more dilute mixture would answer the purpose equally 

 well, so it has been abandoned for the mixture which may now 

 be termed 



The " Normal" or 1.6 per cent Bordeaux Mixture. 



Copper sulphate 6 pounds. 



Quicklime 4 " 



Water 45 gallons. 



This formula, or one in which the amount of water varies 

 from 40 to 50 gallons, may now be considered the most popular 

 in America. Sixty gallons of water should be used when 

 spraying peaches. If air-slaked lime is used in place of the 

 fresh article, the amount should be doubled, and even then its 

 use cannot be recommended, since too little is yet known re- 

 garding the composition and action of the mixture prepared 

 in this manner. By a 3.6 per cent Bordeaux mixture is meant 

 one in which the weight of the copper sulphate is equal to 3.6 

 per cent of the weight of the water, considering 1 gallon to 



