July 23. 1917 Toxic Values and Killing Efficiency of Arsenates 



205 



Table IV.- 



-Compar alive results of tests to determine the relative killing efficiency of 

 arsenates 



Kind and strength of 

 solution. 



Lead hydrogen arse- 

 nate (2:50) 



I/cad hydrogen arse- 

 nate (1:50) 



I,ead hydrogen arse- 

 nate (1:100) 



Iiead hydrogen arse- 

 nate (1:400) 



Lead hydrogen arsenic 

 (1:800) 



Lead hydrogen arse- 

 nate (1:1, 200) 



Basic lead arsenate 

 (i:so) ■ 



Basic lead arsenate 

 (1:50) 



Basic lead arsenate 

 (1:400) 



Calcium arsenate (2:50). 



Calcimn arsenate (1:50). 



Calcium arsenate ( i :40o) 



Calcium arsenate (1:800) 



Number of 

 days after 

 being intro- 

 duced that 

 first cater- 

 pillars died. 



Small 

 cater- 

 pillars. 



Ma- 

 ture 

 cater- 

 pillars. 



Percentage 



of cater- 

 pillars dead 

 first day 

 of drop. 



Small 

 cater- 

 pillars. 



4-S 

 2.94 



.46 



1.58 



I- 55 



2.17 



1.52 



•34 

 3-28 



Ma- 

 ture 

 cater- 

 pillars. 



6.36 



2.74 



8.25 



.50 



1.08 



.68 



26.6s 



18.00 



26.53 



12.56 



6.13 



1. 17 



Total num- 

 ber of days 

 tokiU. 



Small 

 cater- 

 pillars. 



Ma- 

 ture 

 cater- 

 pillars. 



Approximate 

 amount of 

 total arsenic 

 devoured per 

 1,000 cater- 

 pillars. 



Small 

 cater- 

 pillars. 



Mgtn. 



•1595 



•1633 



.1519 



•39" 



■ 4860 



•1139 

 («) 



Mature 

 cater- 

 pillars 



Mgtn. 

 11.815 



7-395 



3-995 



1-870 



1. 700 



2. 040 

 .486 



5-355 



Ratio of arsenic 

 pentoxid in tissue 



is to arsenic pen- 

 toxid in excrement. 



Small 

 cater- 

 pillars. 



1:1. 2100 

 1:1.3888 

 1:1. 6660 

 1:2.3230 

 1:1. 7650 



Mature 

 cater- 

 pillars. 



I :o. 5440 

 i: -7058 

 i: -3055 

 I : ■ 6900 

 I : . 6660 

 i: . 5000 

 1:1. 5100 

 1:1. 2500 



« Excrement not analyzed. 



These results indicate that the lead hydrogen arsenate is the best spray 

 for rapid effective killing, since a larger quantity of the poisonous element 

 is assimilated by the caterpillar than either of the other types. Assum- 

 ing that the lead hydrogen arsenate approximates closely an efficient 

 insecticidal spray and calculating from the figure obtained as given in 

 the above tables at the dilution i to 400, we may generalize as follows 

 relative to the specific amount of arsenic pentoxid necessary to kill a 

 certain number of caterpillars: It required approximately 0.1595 mgm. 

 of arsenic pentoxid to kill 1,000 of the small tent caterpillars and 1.87 

 mgm. to kill a like number of the nearly mature larvae. It is also inter- 

 esting to note that, although a large percentage of the basic lead arse- 

 nate passes through the intestinal tract, the total amount of arsenic pen- 

 toxid devoured is about the same as for lead hydrogen arsenate — namely, 

 0.1 1 39 mgm. for 1,000 caterpillars. It is supposed from the data, there- 

 fore, that it takes approximately the same quantity of arsenic, whether 

 from lead hydrogen or basic arsenate, to kill equal numbers of cater- 

 pillars, but the amount varies greatly, depending upon the size of cater- 

 pillars used. 



FIELD EXPERIMENTS WITH CALCIUM ARSENATE 



Since but limited work has been done on the effects of calcium arse- 

 nate as a spray under climatic conditions existing in the Pacific North- 

 west, a preliminary field test was made in connection with the preceding 



