534 
Journal of Agricultural Research 
Vol. XXIV, No. 6 
bination with them on very tender foliage. The fact that lime sulphur 
decreases the injury caused by calcium arsenite appears to be of only 
scientific interest, for even with this addition the burning will be so 
severe that this arsenical is not useable under most circumstances. 
Tobacco extract gives no increase in the injury by any of the arsenicals. 
Of the environmental conditions, only humidity seems to be of large 
significance, for while the burning is increased in a measure by a rise in 
temperature, it is doubtful if this tendency is great enough within the 
range of temperatures encountered in the field to be entitled to practical 
consideration. The effect of humidity, however, can hardly be over¬ 
rated and must be given large consideration in all spraying operations, 
To be sure, this factor is not under the control of the orchardist and 
farmer, but he can make a fair estimate of the humidity that is likely 
to prevail following spraying in his locality, and be bold or cautious in 
the selection of his spraying material. 
The varying results observed in this investigation when spraying ex¬ 
periments were repeated under conditions identical, except as to weather, 
show the significance of atmospheric conditions, but, what is of especial 
importance to the investigator, these varying results show the great 
danger in drawing conclusions from single experiments. 
SUMMARY 
Based on an investigation extending through a period of lo years, and 
involving the application of various arsenical spray mixtures to approxi¬ 
mately 10,000 separate plants and branches of trees sprayed individ¬ 
ually, we submit the following conclusions concerning arsenical injury to 
foliage: 
(1) The name commonly used does not indicate the composition of an 
arsenical with sufficient exactness. This is especially true of the calcium 
arsenites, lead arsenates, and zinc arsenites, in which the results ob¬ 
tained by using different lots labeled the same except as to manufac¬ 
turer may give widely divergent results. The arsenic trioxids and Paris 
greens are much more uniform in composition. 
(2) The arsenical insecticides least injurious to foliage are iron arsenate 
and certain of the lead arsenates. Possibly new ones will be proposed 
that will be as safe or safer. 
(3) Of the lead arsenates not all pure diplumbic ortho-lead arsenates 
are identical in burning properties, nor are all triplumbic ortho-lead 
arsenates identical in this respect, ^me diplumbic lead arsenates are as 
safe to use as some of the triplumbic ones. 
(4) Arsenic trioxid is not so dangerous to the foliage as is generally 
supposed, and indeed this compound is permissible as an insecticide on 
any but the most delicate foliage, provided it is applied promptly after 
mixing with water. 
(5) Standing after mixing causes a very marked increase in injury by 
arsenic trioxid and a slight increase in injury by other arsenical in¬ 
secticides. 
(6) Of the readily soluble arsenical compounds cacodylic acid and 
sodium and potassium cacodylates proved Ae most injurious. This is 
quite in contrast to the well recognized fact that these compounds of 
arsenic are less harmful to the higher animals than most others. 
(7) The foliage is more susceptible to arsenical injury than the fruit 
or the stems. 
