ACTION OF LEAD ARSENATE ON FOLIAGE. 27 



Sample No. 1 agrees closely in composition with a mixture, in 

 about equal proportions, of tri-plumbic arsenate (Pb 3 (AsO 4 ) 2 ) and 

 plumbic hydrogen arsenate (PbHAsO 4 ), while No. 2 corresponds very 

 closely to the theoretical composition of plumbic hydrogen arsenate. 



EXPERIMENTAL WORK OF 1907. 



The experiments were carried out on trees in the Bureau of Ento- 

 mology orchard on the Department farm at Arlington, Va. Two 

 types of fruit trees were selected, namely, apple, which is one of the least 

 susceptible to injury from arsenicals, and peach, which is the most 

 tender and easily injured of all fruit foliage. The only apple trees 

 available for the experiments were young trees about 6 feet high, 

 which had not reached the bearing age. The peach trees were large 

 and had borne several crops of fruit. In applying the mixtures an 

 ordinary barrel-sprayer outfit, fitted with a "Vermorel" double noz- 

 zle, was employed. For each experiment there were used six apple 

 and six peach trees. These were divided into two sections: A (three 

 trees) received two applications and B (three trees) received three 

 applications. 



DESCRIPTION OF EXPERIMENTS. 



Experiment ITo test the effect of pure lead arsenate made from sodium arsenate 

 and lead acetate. Applied the material at the rate of 1J pounds of dry lead arsenate 

 to 50 gallons of water. This is equivalent to about 2 pounds of a good grade of com- 

 mercial lead arsenate to 50 gallons of water. 



Experiment 2. Same as Experiment 1, except that freshly slaked quicklime was 

 added at the rate of 4 pounds to 50 gallons of the spray mixture. (To determine to 

 what extent the presence of lime would lessen or prevent burning of the foliage.) 



Experiment 3. Same as Experiment 1, except that lead nitrate instead of the 

 acetate was used in the preparation of the lead arsenate. (To show whether lead 

 arsenate made from lead nitrate has a different action from lead arsenate made from 

 lead acetate.) 



Experiment 4. Same as Experiment 3, except that quicklime was added at the rate 

 of 4 pounds to 50 gallons. 



Experiment 5. To determine whether sodium acetate and acetic acid, which are 

 formed as by-products when lead acetate acts on sodium arsenate, will scorch foliage. 

 Applied a mixture of sodium acetate and acetic acid in the proportion of 9.6 ounces 

 of crystallized sodium acetate and 2.9 ounces of anhydrous acetic acid to 50 gallons of 

 water. (These are the respective amounts of sodium acetate and acetic acid obtained 

 in the making of 1J pounds of dry lead arsenate, assuming that tri-plumbic arsenate 

 is formed.) 



Experiment 6. To determine whether the amount of sodium acetate.used in Experi- 

 ment 5, when used alone, will injure foliage. (Applied wash in the proportion of 9.6 

 ounces to 50 gallons.) 



Experiment 7. To determine whether sodium nitrate, which is formed as a by- 

 product when lead arsenate is made from sodium arsenate and lead nitrate, will injure 

 foliage. This was applied in the proportion of 10.4 ounces to 50 gallons of water, the 

 theoretical amount of sodium nitrate formed in making 1J pounds of dry lead 

 arsenate, using lead nitrate and assuming that plumbic hydrogen arsenate is formed. 



