ARSENICALS. 
51 
arsenate combination, six times as much arsenic is formed as in the 
calcium arsenate combination. Acid lead arsenate, therefore, should 
not be used in preparing kerosene-emulsion sprays, as the mixture is 
chemically incompatible. Gray (16) reports that basic lead arsenate 
is not affected by the alkali of soap. 
When acid lead arsenate was mixed with solutions of nicotine sul- 
phate, no chemical incompatibility was found. When calcium 
arsenate was used with nicotine sulphate, however, the latter was 
decomposed and free nicotine was formed. The S0 4 of the nicotine 
sulphate combined with free lime (CaO) , if present, or with lime of the 
calcium arsenate, and large amounts of soluble arsenic were formed 
in certain mixtures. Free nicotine is present in all of these mixtures. 
The free nicotine is not dangerous but the soluble arsenic is. These 
mixtures are chemically incompatible. The findings in connection 
with the chemical compatibilities and incompatibilities of the various 
arsenicals, fungicides, and other materials tested are summarized in 
Table 23. Gray (16) in 1914 published a summary of data on the 
compatibilities of various spray materials which he had collected. 
Table 23. — Chemical compatibility of arsenicals combined with other spray materials. 
Other spray materials used. 
Arsenicals used. 
Lime sulphur. 
Bordeaux 
mixture. 
Kerosene 
emulsion. 
Sodium fish- 
oil soap. 
Nicotine-sul- 
phate solution. 
Acid lead arsenate — 
Calcium arsenate 
Incompatible... 
Compatible 
Compatible . 
do 
do 
Incompatible... 
do 
Incompatible... 
do 
Compatible. 
Incompatible. 
do 
Sanders and Brittain (41) tested the comparative insecticidal prop- 
erties of the arsenates of calcium, barium, and lead, alone and in com- 
bination with Bordeaux mixture, lime-sulphur, barium tetrasulphid, 
and sodium sulphid (" soluble sulphur"), on one species of insects. 
The results obtained showed that the presence of a fungicide had a 
marked influence on the efficiency of the arsenical investigated. The 
four arsenicals were 13 per cent more efficient when used with sodium 
sulphid than when used alone. The toxicity of the arsenicals was 
reduced when they were mixed with any of the other fungicides. The 
explanation given by these authors for the increased toxicity resulting 
from the use of sodium sulphid with an arsenical is that the sodium 
increases the palatability of the sprayed leaves, which causes the 
insects to eat ravenously for a few days. The insects thus take a large 
amount of arsenic into their systems in a short time and death rapidly 
ensues. 
Mixing sodium sulphid with acid lead arsenate produces some lead 
sulphid and sodium arsenate. The sodium arsenate is soluble and 
therefore may be more active than the original acid lead arsenate. 
The results in Table 21 indicate that the soluble arsenicals are more 
toxic per unit of arsenic than are the insoluble ones, the greater 
toxicity being due to the water-soluble arsenic present in the com- 
pound or to the arsenic which is quickly rendered soluble inside the 
insects. Data obtained during this investigation suggest that the 
amount of arsenic present per unit of sprayed leaf is larger when a 
