REPORT OF THE SOCIETY 41 



CHEMICAL INVESTIGATION OF SPRAYS 



A. Kelsall 



Most of our knowledge on the efficiency and action of insecticides and 

 fungicides has been derived from actual field observations. That is to say, many 

 materials have been tried and their action upon plant pests noted, and their 

 action upon plant foliage noted. Following such methods there has, during 

 the past many years, accumulated a vast amount of information on the use of 

 many materials as insecticides and fungicides. The reason why certain mat- 

 erials act as they do is often imperfectly understood. Much light has, however, 

 been thrown on this by the chemical investigations of numerous experimenters. 

 In France and England the chemistry of Bordeaux mixture has been thoroughly 

 studied, and much of our knowledge of insecticide arsenicals we owe to the chem- 

 ists of the U. S. Insecticide and Fungicide Board. The greatest bulk of 

 materials used in plant pest suppression, consists of compounds of arsenic, of 

 copper, of sulphur and of nicotine. In this brief address, I will just touch on 

 some of the salient points of these arsenic, copper and sulphur compounds, 

 presenting some information which has been long known and some of more 

 recent origin. 



Commencing with arsenical insecticides, it may be stated that an arsenical 

 to be an efficient insecticide for application to foliage, must possess the following 

 qualifications : 



1. It must be soluble in the digestive juices of the insect, otherwise it will 

 not kill. 



2. It must, as nearly as possible, be insoluble in water, or it will injure the 

 foliage. 



The insecticide which best fulfills these conditions is lead arsenate. 



Lead Arsenate 



Lead arsenates have, in the past, been placed upon the market in three 

 forms, or generally as some mixture of three forms. 

 These consist of the compounds : 



Pb H ASO4 di-lead arsenate. 



Pbs (ASO4) 2 tri-lead arsenate. 



Pb4 (PbOH) (As04)3 basic lead arsenate. 



Of these three, all are satisfactory insecticides, but the latter two, owing 

 to the smaller amount of arsenic they contain and to their more expensive nat- 

 ure, have been largelj'- discarded, and manufacturers aim to produce the com- 



