﻿50 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



stained, while all the tissues outside the intestinal wall contained 

 more or less of the stain. In the larvae fed lampblack much of the 

 powder could be observed inside the intestine, but very little (perhaps 

 none in reality) outside the intestinal wall. 



GENERAL PROPERTIES OF ARSENICALS. 



Used alone, arsenious oxid burns the most resistant foliage, 

 because of its high percentage of water-soluble arsenious oxid. To 

 overcome this difficulty, Sanders and Kelsall (43) mixed a very finely 

 divided arsenious oxid with Bordeaux mixture, to serve as a sub- 

 stitute for sodium arsenate and Bordeaux mixture, to control the 

 potato beetle and late blight in Nova Scotia. Cooley (13) suggested 

 the use of white arsenic with Bordeaux mixture for dusting potato 

 vines and has successfully used white arsenic as a substitute for the 

 expensive Paris green in bran mash to control grasshoppers in 

 Montana. He considers crude arsenious oxid to be superior to the 

 refined product, as the particles are finer. Most authors think that 

 arsenious oxid possesses high insecticidal properties. The results of 

 the investigation here reported, however, indicate that the toxicity 

 of arsenious oxid varies greatly, depending on the degree of fineness 

 of the crystals which influences the percentage of water-soluble 

 arsenious oxid present. In no case did the toxicity equal that of an 

 equivalent amount of arsenic oxid present in acid lead arsenate. 



Acid lead arsenate, a satisfactory insecticide material, is to be 

 recommended in general when an uncombined arsenical is to be used, 

 as it possesses excellent adhesive and insecticidal properties, and 

 burns foliage little if at all. Acid lead arsenate is compatible with 

 Bordeaux mixture and with nicotine sulphate solutions. Lime- 

 sulphur and acid lead arsenate are incompatible from a chemical 

 standpoint, some soluble arsenic being formed. However, it is well 

 recognized that acid or basic lead arsenates are used with lime- 

 sulphur without serious foliage injury in most cases. A powdered 

 acid lead arsenate contains about 32 per cent of arsenic oxid and 

 about 64 per cent of lead oxid, while powdered basic lead arsenate 

 contains aDout 23 per cent of arsenic oxid and about 73 per cent of 

 lead oxid. Also, basic lead arsenate is more stable and less toxic 

 than acid lead arsenate. 



Paris green, a valuable insecticide on account of its high arsenic 

 content, is said to dust well in spite of its high apparent density, but 

 not to adhere well to foliage. It has no advantages over acid lead 

 arsenate, but has several disadvantages, the burning of foliage being 

 the principal one. The expensive copper sulphate and acetic acid 

 used in its manufacture do not increase its power as a poison. 



The amount of soluble arsenic in an arsenical is reduced by mixing 

 it with Bordeaux mixture, and an unsafe arsenical may in certain 

 cases be made safe by mixing it with Bordeaux. 



Soaps contain alkalies which decompose arsenicals. The more 

 soap used, the greater the decomposition. When calcium arsenate 

 was mixed with sodium fish-oil soap, a smaller amount of soluble 

 arsenic was formed than when acid lead arsenate was used in the 

 mixture. Both of these mixtures are incompatible. 



When acid lead arsenate or calcium arsenate is used in a kerosene- 

 soap emulsion, soluble arsenic is rapidly formed. In the acid lead 



