H INSECTS OF ECONOAIIC IMPORTANCE 



Arsenate of lead ^^ 



The paste form — Was first used in fighting in- 

 sects in New England in 1893. 



A compound "" of arsenic oxide and lead oxide ; 

 remains in suspension better than paris green; is 

 white in color and leaves a mark on foliage; will 

 not ordinarily burn foliage; sticks to plant tena- 

 ciously; several applications may injure peach foli- 

 age. 



The commercial brands vary from 12% to over 

 20% of arsenic oxide ^^ — the average being about 

 15%. They usually contain less than 1% soluble 

 or free arsenic. 



Chemically, arsenate of lead may be (i) of 

 the lead hydrogen, or acid, or plumbic form 

 PbHAs04 or (2) of the basic, neutral, or triplum- 

 bic form, Pb3(As04)2. Usually the commercial 

 brands are a mixture of these two forms although 

 the acid lead often predominates. The acid lead, 

 when mixed with lime-sulphur for a summer spray, 

 tends to pass through a chemical reaction and form 

 soluble arsenic which is likely to cause burning of 

 the foliage. At the same time the sulphur con- 

 tent of the solution is decreased and its fungicidal 

 value lessened. On the other hand the basic, or 

 neutral lead when combined with lime-sulphur does 

 not have a tendency to form soluble arsenic and it 

 is therefore safer on foliage although not quite so 

 rapid in its effect as a poison. The addition of lime 

 will largely prevent the acid lead from reacting. ^^ 



Injury to foliage by arsenate of lead — The 

 water in which the arsenate of lead is suspended 

 seems to have some determining effect upon the in- 



21 Burgess and Rogers— U. S. Bu. Ent., Bull. 87, p. 17. 



22 Smith— New Jersey Expt. Stat., Bull. 213, p. 11. 



23 Haywood and McDonnell— U. S. Bu. Chcm., Bull. 131. 



24 Robinson— Jr. Ec. Ent., Vol. 12, p. 429. 



