46 LEAD ARSENATE. 



TABLE X. Results of experiments with carbon dioxid. 

 [Arsenic in solution expressed as AszOs.] 



Carbon-dioxid-free water: Per cent. 



Experiment 1 . 0.40 



Experiment 2 49 



Water with carbon dioxid added: 



Experiment 3 25 



Experiment 4 39 



Water with carbon dioxid added and warmed to 50 0.: 



Experiment 5 33 



Experiment 6 43 



It will be seen from these experiments that lead arsenate is slightly 

 less soluble in distilled water saturated with carbon dioxid, even when 

 heated to 50 C., than in cold distilled water free from carbon dioxid. 

 It would hardly be expected that the results could be otherwise on 

 the tree. 



EXPERIMENTS ON THE SOLVENT ACTION OP WATER USED IN SPRAYING. 



It was then thought that possibly the water with which the lead 

 arsenate was being mixed for spraying contained compounds that 

 had a solvent action on the lead arsenate. To determine this and 

 also at the same time to determine the action of dilute solutions of 

 sodium chlorid and sodium carbonate (two salts occurring fre- 

 quently in waters) on lead arsenate, the following experiments were 

 made: 



Experiment 1. One gram of lead arsenate, made from lead acetate, was treated 

 with 1,000 cc of the water which was used in the spraying experiments, and allowed 

 to stand at room temperature ten days, shaking it eight times each day. This wat 

 filtered and the amount of arsenic in the solution determined. 



Experiment 2. Same as Experiment 1, except that lead nitrate was used in making 

 the lead arsenate. 



Experiment 3. Same as Experiment 1, except that the mixture was heated to abou 

 50 C. each day for ten days. 



Experiment 4. Same as Experiment 2, except that the solution was heated as ii 

 Experiment 3. 



Experiment 5. Same as Experiment 1, except that the lead arsenate was treatec 

 with 1,000 cc of distilled water, carbon-dioxid-free, in which had been dissolvec 

 2 grams of pure sodium chlorid. 



Experiment 6. Same as Experiment 5, using lead arsenate prepared from leac 

 nitrate. 



Experiment 7. Same as Experiment 1, except that 1,000 cc of distilled water con 

 taining in solution 2 grams of pure sodium carbonate was used. 



Experiment 8. Same as Experiment 7, using lead arsenate prepared from lea< 

 nitrate. 



The amount of arsenic in solution and the per cent based on thi 

 total arsenic present are given in the following table: 



