TWENTY-FIRST ANNUAL MEETING. 



207 



ordinary mixed lead arsenates before combining them with 

 the lime-sulphur solution. The best form of lead for this 

 purpose is probably the acetate or "sugar of lead," as the 

 nitrate has been known to cause some injury itself. 



The amount of extra lead actually required for safety 

 depends on the per cent of soluble arsenic and acid arsen- 

 ates present in the given sample and also on the amount 

 of free lead already present. In general, however, four 

 to six ounces of the acetate should be sufficient to render 

 safe two pounds of ordinary lead arsenate paste or its equiv- 

 alent in the powdered form. 



The effect of this addition is really to form the ortho- 

 arsenate in the spray tank from the arsenic acid referred 

 to above, although probably some calcium arsenate is also 

 formed.* The latter is less desirable, as is also the arsen- 

 ite of lime, even when made with the lower amount of 

 soda recommended in our Bulletin 99. If one does not 

 wish to make this addition of lead to present Eastern com- 

 mercial lead arsenates, then he should insist on getting 

 the ortho-arsenate. It has been made for a number of 

 years on the Pacific Coast^ for use especially in the trying 

 conditions of the Pajaro Valley in California, and certain 

 firms are now contemplating its manufacture in the East. 

 It also is not especially difficult to make locally and to 

 prove its nature, though it requires some chemical training 

 and proper laboratory facilities. Its preparation is de- 

 scribed later. 



Its insecticidal value is at least not inferior to that of 

 the ordinary lead arsenates, since our two "ortho" plots 

 averaged only 6.6% of curculio injury as compared with 

 8.2% on the latter. Tt takes about two and one-half pounds, 

 however, to carry the same amount of arsenic as two pounds 

 of the ordinary mixed lead arsenates. 



* The firm making it on the Coast is the California Spray-Chemical Co., Wat- 

 sonville, Cal. The material used by us was made and tested in the Pennsylvania 

 State College laboratories by Mr. F. P. Weaver, of the Agricultural Chemistry 

 Department, largely after the directions given in the article referred to in foot- 

 ■note 1. 



