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 cr} 7 stals 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 about 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. 
k 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 
