192 Journal of Agricultural Research voi. xxvi, No. 4 
follow standard procedures. Femald and Bourne, 4 after observations 
of lead arsenate spraying extending over a period of 12 years, state that 
the injury to such tender foliage as that of peach and plum is influenced 
by both temperature and humidity. They have defined the limits of 
the temperature-humidity relation within which it is safe, and beyond 
which it is unsafe, to use lead arsenate on such trees. 
Certain chemical factors also are of importance, particularly the quan¬ 
tity and character of the salts in the water with which a material is 
applied. The reaction of these salts with the arsenical may liberate 
large quantities of soluble arsenic. 5 Haywood and McDonnell 6 have 
pointed out the susceptibility of dilead arsenate to alkali carbonates and 
soluble chlorids, and McDonnell and Smith 7 have shown the nature of 
the reaction in the case of the chlorids. Their work suggests that the 
burning by dilead arsenate frequently observed on the Pacific coast, and 
hitherto attributed to hydrolysis by the heavy and recurring fogs of that 
region, is really due to the salt spray entrapped by these fogs. 
Granting the possibility of decomposition of the arsenical by salts in 
the water used and by material deposited from the air, may the plant 
contribute to the injurious tendencies by furnishing other substances 
capable of causing decomposition? Patten and O’Meara, 8 recognizing 
this possibility, suggested that the carbon dioxid given off by the leaves 
might be a factor. Their experiments showed that calcium arsenate 
was very sensitive to aqueous carbon dioxid solutions, giving much 
more “soluble arsenic” than could be dissolved under similar conditions 
in pure water. 
RELATION OF DEW TO ARSENICAL INJURY 
The occasional burning which could not be traced to poor material, 
usually most pronounced when the dew was heaviest and drying rapidly 
in the morning, and observed during dusting experiments with calcium 
arsenate, led to an examination of dew on cotton leaves. Instead of an 
acid reaction, as would have been the case had the expected free carbon 
dioxid been present, the dew gave a reaction alkaline even to phenolph- 
thalein, indicating the presence of soluble hydroxid or salts of very weak 
acids. In each of the many tests made in different localities the result 
was the same. The alkalinity seemed to be localized around the main 
ribs of the leaves. The soil in the cotton fields and that in the neigh¬ 
boring roads did not give an alkaline reaction, so that the effect could 
not have been due to dirt splashed up from the ground by the rain or 
blown on by the wind. Dew from many other plants, including corn, 
china berry, grass, cocklebur, and several other weeds in the same fields 
was likewise tested. In no case was the reaction alkaline. It would 
therefore appear that the condition is natural and perhaps peculiar to 
the cotton plant, at least in the region around Tallulah, La., where these 
observations were made. 
4 Fernand, H. T., and Bourne, A. I. injury to foliage by arsenical sprays. I. The lead arsen¬ 
ates. Mass. Agr, Exp. Sta. Bui. 207, 19 P-. 23 fig. 1922. 
6 Ong, E. R. de. the relation op hard and alkaline waters to the preparation and dilution 
OP sprays and dips. In Jour. Econ. Ent., v. 15, p. 339-345* 1922. 
6 Haywood, J. K.. and McDonnell, C. C. lead arsenate. U. S. Dept. Agr. Bur. Chem. Bui. 131, 
p. 46. 1910. 
7 McDonnell, C. C., and Smith, C. M. the preparation and properties of lead-chlor arsenate, 
artificial mimetitb. In Amer. Jour. Sci., v. 42, p. 139-145. 2 fig. 1916. 
8 Patten, Andrew J.,and O’Meara, P. the probable cause of injury reported from the use 
OF calcium and magnesium arsenates. In Mich. Agr. Exp. Sta. Quart. Bui., v. 2, p. 83-84. 1919. 
