HOME-MADE LEAD ARSENATE. 19 



the lead salt in excess, but in most of them no reference is made to 

 this point. In the majority of the formulas, however, the amount 

 called for is considerably in excess of the theoretical. This, of course, 

 results in a waste of the lead salt, except in rare instances, where 

 sodium arsenate containing an unusually high per cent of arsenic is 

 being used. In such a case there might not be sufficient lead to 

 combine with all of the arsenic, thus leaving the soluble arsenic salt 

 in excess and yielding a product that would cause injury to most 

 foliage to which it might be applied. 



PUBLISHED FORMULAS. 



A number of formulas for making lead arsenate have been pub- 

 lished in the various experiment station bulletins, governmental 

 reports, and works on economic entomology. These, as a rule, call 

 for lead acetate as the lead salt and show considerable variation in 

 the relative proportion of the lead and arsenic salts. The various 

 proportions which have been recommended are given below, with the 

 number of publications in which they have appeared placed in paren- 

 theses. The original proportion given by Moulton a and which was 

 followed for the preparation of the arsenate of lead used by the Mas- 

 sachusetts gypsy moth commission, was sodium arsenate 29.93 per 

 cent and lead acetate 70.07 per cent, or sodium arsenate 3 ounces and 

 lead acetate 7 ounces. This formula has been repeated in thirteen 

 publications. Another proportion, recommended by Fernald b and 

 found by the authors to have been more frequently recommended 

 than any other (26 cases) is arsenate of soda 4 ounces and acetate of 

 lead 11 ounces. 



The following formulas have also been found: 



Arsenate of soda. Acetate of lead. 



Oz. Oz. 



4 10 (1) 



4 12 (1) 



2 7J(1) 



6 18 (1) 



8 24 (3) 



10 25 (1) 



10 24 (5) 



Formulas using arsenate of soda and nitrate of lead have been given 

 as follows: 



Arsenate of soda. Nitrate of lead. 



Oz. Oz. 



5 10 (4) 



12 18| (1) 



10 24 (3) 



Agriculture of Massachusetts, 1893, p. 282. 

 & Massachusetts Hatch Exper. Sta., Bui. 24. 



