ARSENICALS. 33 
the addition of lime to the three arsenicals employed reduced the 
toxicity in practically all cases. 
There are two possible explanations for the reduction in toxicity 
due to the addition of lime. The excess lime may unite with the 
soluble arsenic and prevent it from functioning as a poison. This 
explanation is supported by practically all the results recorded, 
providing the excess lime did not decrease the percentage of arsenic 
in the food or on the leaves eaten. It did not reduce the percentage 
of arsenic in the poisoned honey, yet the lime in every case caused 
a decrease in toxicity to honeybees. In the case of the leaf-eating 
insects, the lime added theoretically reduced the percentage of 
arsenic on the leaves, because 2 grams of lime were mixed with every 
gram or less of the arsenical. Consequently, the dried spray material 
on the leaves would be greatly adulterated and the percentage of 
arsenic in it would be lowered. To determine the extent of the 
decrease in the arsenic, many leaves were sprayed with samples 
39, 39C, 69, 69C, 64, and 64C. After repeating these experiments 
three times and analyzing the 18 samples of leaves sprayed, it was 
found that the addition of lime had reduced the arsenic on the leaves 
26.3 per cent, while the excess lime on other leaves similarly sprayed 
had reduced the average toxicity of the same three arsenicals only 
21.1 per cent. 
In order to prevent the decrease of arsenic on the leaves, at the 
same time retaining an excess of lime on them, the following experi- 
ments were performed. Many leaves were sprayed, some with acid 
lead arsenate (sample 39) and others with calcium arsenate (sample 
57). When dry, half of each lot was again sprayed with lime (sample 
1 1 ) (2 grams of calcium oxid in 4 18 cubic centimeters of water) . When 
all the leaves were dry, half of them were prepared as samples to 
be analyzed for arsenic and the other half were fed to fall webworms. 
These experiments were repeated twice, using 8,888 webworms in 
all. The results in Table 14 show that the lime (sample 39L) did 
not affect the toxicity of the acid lead arsenate (sample 39), but it 
(sample 57L) reduced the toxicity of the calcium arsenate (sample 57) 
50 per cent. Analyses of the leaves sprayed with samples 39 and 
39L showed that the lime reduced the arsenic 18 per cent, while in 
those sprayed with samples 57 and 57L the arsenic was reduced 
29.4 per cent. 
EFFECT ON TOXICITY OF ADDING BORDEAUX MIXTURE AND LIME-SULPHUR TO ARSENICALS. 
Sanders and Brittain (41) reported that Bordeaux mixture and 
Wilson (51) reported that lime-sulphur, when added to arsenical 
spray mixtures, decrease the killing power of the arsenicals. Many 
experiments were performed by the writers in 1919 to determine 
whether or not these statements were true. The following insects 
were used: Webworms (H. cunea), 1 set (variation 102-476, average 
241); tent caterpillars, 4 sets (742-1187: 919); and potato-beetle 
larvae, 2 sets (130-264:153). After deducting the mortalities of the 
controls, the average percentages of toxicity of the three species of 
insects used are as follows : Sample 68 (laboratory sample of acid lead 
arsenate), 47.1 ; sample 50 (sample 68 plus lime sulphur), 40.1 ; sample 
69 (laboratory sample of calcium arsenate), 55.6; sample 53 (sample 69 
