574 STATE BOARD OF AGRICULTURE. 



usually expressed in terms of crystallized copper sulfate or blue vitriol. 

 The formula most commonly used is 4-4-50 meaning 4 pounds eacli of 

 crystallized copper sulfate and quick lime and 50 gallons of water. 



The State and Federal insecticide laws require the strength of commer- 

 cial bordeaux to be expressed in terms of metallic copper. This moans 

 little to the person who is unfamiliar with the chemical relationships in- 

 volved. When the strength of the commercial bordeaux mixture is ex- 

 pressed as metallic copper the equivalent amount of crystallized copper 

 sulfate (blue vitriol) may be quickly obtained by multiplying the percent- 

 age of metallic copper (Cu) by the factor 'A.U.i. If Die strength is ex- 

 pressed as copper oxide (CuO) or copper hydroxide (Cu(OH).) multiply 

 by the factors 3.14 and 2.56 respectively. The result obtained will repre- 

 sent the amount of crystallized copper sulfate equivalent to guaranteed 

 percentage of copper in the various forms as expressed on the label. To 

 calculate the amount of copper sulfate in the spray mixture when diluted 

 and ready for application, multiply the percentage of copper sulfate as 

 found by the number of pounds of the concentrated bordeaux mixture to 

 be added to 50 gallons of water. 



The following example will serve to illustrate the process as outlined. 

 A sample of commercial bordeaux mixture, found on the market, was guar- 

 anteed to contain 7.50 per cent copper (Cu), which, multiplied by the 

 factor 3.93 equals 29.48 per cent crystallized copper sulfate. One pound 

 of the preparation, therefore, would contain 0.2948 pounds of crystallized 

 copper sulfate. The label recommends that 8 pounds of the mixture be 

 diluted to 50 gallons with water. The amount of crystallized copper sul- 

 fate in the 50 gallons of diluted spray mixture is found by multiplying 

 0.2948 by 8 which equals 2.16 pounds. 



This particular bordeaux mixture, when diluted according to directions, 

 would give a spray mixture a trifle stronger than a 2-2-50 formula. 



Knowing the price of crystallized copper sulfate and quick lime at any 

 given point the actual money value of the commercial mixtures can easily 

 be calculated. This, of course, will vary in different localities owing to 

 variations in the prices of the raw materials. 



Physical Condition. The second factor in determining the value of com- 

 mercial bordeaux mixtures is their physical condition. This condition 

 determines the spreading and sticking properties of the mixture and is 

 measured by the rate at which the suspended material settles. A well 

 made bordeaux mixture, will, upon dilution, remain in suspension a long 

 time but some of the commercial preparations will settle almost immedi- 

 ately. The commercial preparations will be found to vary considerably 

 in this characteristic. Before buying any quantity of commercial bor- 

 deaux this test should be applied to a small sample. In making this test 

 the dilution should be made in the same proporticui as recoinmeiided ou 

 the label for preparing the material for spraying. 



HOW TO CALCULATE THE STRENGTH OF BORDEAUX-LEAD ARSENATE MIXTURE 



In materials of this kind the law requires the manufacturer to guar- 

 antee the amount of lead arsenate both total and water-soluble in terms of 

 metallic arsenic (As). In order to convert this into lead arsenate (dry 



