26 



LEAD ARSENATE. 



age in some States may be used with safety in others. The injury 

 to foliage from arsenicals in arid regions is less than in non-arid 

 regions. Atmospheric conditions following spraying have a great 

 influence on the action of the spray mixture on the foliage. As to 

 why these conditions cause such variations in results no satisfactory 

 explanation has ever been given. It is well known to chemists that 

 pure arsenate of lead is practically insoluble in pure water, and it 

 seems impossible that it can cause injury as long as it remains so. 

 It has never been proven that leaves can absorb insoluble substances, 

 but investigators have shown conclusively that they do absorb salts 

 in solution. It would appear, therefore, that the lead arsenate must 

 be acted upon by some solvent, rendering more or less of the arsenic 

 soluble, before burning of the foliage will result. It was for the pur- 

 pose of determining this important point, if possible, that this inves- 

 tigation was begun. In order that the experiments may be carried 

 out under the varying conditions presented by different seasons, it 

 is the intention to conduct them for a number of years in succession, 

 and while it is considered that the results obtained from the experi- 

 ments conducted and reported herein are extremely suggestive they 

 are not given as conclusive, but on account of the importance of the 

 subject are presented as showing the progress that has been made. 



PREPARATION OF THE LEAD ARSENATE USED. 



That there might be no doubt of the purity of the lead arsenate 

 used, it was prepared in the laboratory from pure chemicals and 

 thoroughly washed. The product was then dried in order that it- 

 might be more conveniently handled and accurately weighed. 



No. 1 was made by adding a solution of crystallized lead acetate to 

 a solution of crystallized sodium arsenate until the lead salt was in 

 slight excess. The precipitated lead arsenate was allowed to settle, 

 the supernatant liquid decanted, then the material was washed by 

 decantation with pure water, and finally filtered and washed till the 

 greater portion of the soluble impurities were removed, after which 

 it was dried and powdered. 



No. 2 was prepared in the same way, except that pure lead nitrate 

 was used instead of lead acetate. On analysis the samples showed 

 the following composition : 



TABLE V. Analysis of lead arsenates prepared in the laboratory. 



