﻿38 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



and comparing the toxicity of the three Paris greens with that 

 of the lead arsenate, it is 11.5 per cent more. London purple 

 (sample 90) has an average percentage of toxicity of 63.9, being 

 practically the same as that of zinc arsenite. While this sample 

 killed all of the webworms tested within 20 days, only about 90 per 

 cent of those fed zinc arsenite died during the same period of time. 



RELATIVE TOXICITY OP NEW ARSENATES. 



In making a comparison of the relative toxicity of new arsenates, 

 three commercial products and three pure laboratory products were 

 used. The commercial acid lead arsenate (sample 39) was taken as 

 a standard by which to judge the relative toxicity of the other 

 products. The two other commercial products (sample 70, acid 

 lead arsenate made by a new process, and sample 62, magnesium 

 arsenate) and the laboratory sample of barium arsenate (sample 71) 

 are practically new, while the laboratory samples of arsenates of 

 aluminum (sample 73) and of copper and barium (sample 74) are 

 totally new, as far as known. 



In 1919 the following insects were tested: Silkworms, 1 set of 50; 

 webworms (H. cunea), 1 set (variation 124-195, average 152); web- 

 worms (H. textor), 1 set (189-514, average 314); potato-beetle larvae, 

 2 sets (150-355, average 260) ; and grasshoppers, 2 sets (181-305, 

 average 265). After deducting the mortalities of the controls, the 

 following figures were obtained. When silkworms, webworms (H. 

 cunea), and potato-beetle larvae were tested, the average percentages 

 of toxicity were: Sample 39 (acid lead), 58.2; sample 70 (acid lead, 

 new process), 57.3; and sample 62 (magnesium), 59.8. When silk- 

 worms, webworms (both species) , potato-beetle larvae, and grasshop- 

 pers were tested, the percentages were: Sample 39, 58.8; and sample 

 62,54.2. When webworms (both species), potato-beetle larvae, and 

 grasshoppers were tested, the percentages were : Sample 39,55; sam- 

 ple 71 (barium), 43.6; and sample 74 (copper and barium), 48.9. 

 When webworms (both species) and potato-beetle larvae were tested, 

 the percentages were: Sample 39, 57.2; and sample 73 (alumi- 

 num), 34.6. 



In 1920 these experiments were repeated, with the results shown 

 in Table 18, as well as the following: Silkworms, 2 sets (each of 50); 

 webworms (H. cunea), 2 sets (variation 647-897, average 776); 

 webworms (H. textor), 1 set (189-514, average 314); honeybees, 2 sets 

 (each of 50); and tent caterpillars, 3 sets (240-556, average 337). 



