﻿ARSKNICALS. 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 tonicity 

 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 

 11) (2 grams of calcium oxid in 418 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 {£1) 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 



