﻿ARSENICALS. 43 



34, 46, and 59), lead and calcium arsenates plus lime-sulphur (samples 

 50 and 51), and Paris green. The following slightly burned wild- 

 cherry foliage: Zinc arsenite (samples 23 and 33), zinc arsenite 

 plus Bordeaux mixture (sample 30), calcium arsenate (sample 32), 

 and barium arsenate (sample 71). Zinc arsenite (sample 23) and 

 Paris green slightly burned mulberry foliage. 



RELATION OF ARSENIC RENDERED SOLUBLE BY INSECTS TO TOXICITY OF AR8ENICA/.H. 



Kirkland and Smith (22), in 1897, found that the alimentary 

 tracts of the gypsy moth larvae were alkaline to litmus. Analyses 

 of the dialysate from washed and macerated alimentary tracts 

 showed the presence of phosphorus and potash in proportions suffi- 

 cient to form alkaline potassium phosphate, which is suggested as 

 the cause of the alkaline reaction. Because of the report of these 

 investigators, determinations of the hydrogen-ion concentration 

 (pH value) were made on the water extracts of the bodies of the 

 insects fed various arsenicals and also of the bodies of control in- 

 sects. The results thus obtained showed a comparatively uniform 

 acidity for all the insects tested. It is possible, however, that 

 lactic or other acids are formed in the dead tissues of the insects. 

 The buffer effect normally available may possibly have masked any- 

 slight changes in the reaction caused by the arsenicals fed. It is 

 obvious that the pH data as here obtained, or ash determinations 

 on dialysates of intestinal tracts as made by Kirkland and Smith, 

 are inadequate to show the reactions (pH) of the living tissue of 

 the intestinal tracts of insects. 



The following methods were employed to determine the total 

 arsenic and water-soluble arsenic in insects and also the hydrogen-ion 

 concentration of the water extracts from the insects. The weights 

 and number of the washed larvae were recorded, after which the 

 insects, parts of insects, or feces (dried in an oven at 105° C.) were 

 macerated in a mortar containing about 20 cubic centimeters of dis- 

 tilled water. The macerated larvae were then transferred to flasks 

 and diluted to 500 cubic centimeters with distilled water. The solu- 

 tions were shaken every 5 minutes for an hour, at the end of which 

 they were filtered and aliquots were taken for the determination of 

 the hydrogen-ion concentration and for the water-soluble arsenic. 

 The rest of the solution, with the residue, was used for the total 

 arsenic determination. The hydrogen-ion concentration was deter- 

 mined by the indicator method outlined by Clark and Lubs (8) . The 

 solutions used for determining the soluble arsenic and those with the 

 residues for determining the total arsenic were placed in large por- 

 celain casseroles, and nitric and sulphuric acids were added. They 

 were then warmed on the steam bath and finally heated on the hot 

 plate until the organic material was completely destroyed. Since 

 the acids used, particularly the nitric acid, were not totally free from 

 arsenic, a record of the quantities of acids used was kept. The 

 solutions were then freed from nitric acid by adding water and by 

 applying heat. Next enough water was added to make a volume of 

 100 cubic centimeters, and finally the arsenic was determined by the 

 Gutzeit method, revised by Smith (47) . 



As preliminary tests, the following experiments were performed in 

 1919. Both sides of several mulberry leaves were heavily sprayed 



