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 ARSENICALS. 
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 {4-7). 
As preliminary tests, the following experiments were performed in 
1919. Both sides of several mulberry leaves were heavily sprayed 
