July 1,1925 Spreaders and Spreading Qualities of Spray Materials 77 
obtain values whereby the spreading qualities of a solute may be 
estimated by substituting the surface tension values in the inequality 
just given. 
Although specific deduction can not be made from the surface 
and interfacial tension values regarding the spreading properties 
of various solutes, possibilities may be suggested, especially if the 
chemical composition is taken into consideration. Low values 
indicate in general surface adsorption and all substances tested and 
showing this phenomenon have certain spreading qualities. There 
are probably other influencing factors that affect spreading. Such 
factors as the solvent action of the spreaders on the surface to be 
covered, the rapidity with which static equilibrium is established, 
and the formation of plastic solids at the interface may benefit or 
reduce spreading. 
Further examination of the observations reported in Table II 
discloses why it is difficult to generalize on the spreading qualities 
of any particular substance. It will be seen that some materials 
at a certain dilution spread well on apple leaves, and “medium” 
or “poor” on pears or prune leaves. Other variations are shown as 
“medium” spread on apple and prune leaves, while only “poor” 
spreading is obtained on pear leaves and apple fruit. It was also 
noticed that the age and exposure of the leaf to the sun’s rays in¬ 
fluenced the degree of spreading. For example, a solute at minimum 
concentration would spread nicely on a young apple leaf, while barely 
perceptible spreading would occur on an old leaf taken from the 
exposed side of the tree. In many cases, however, a higher concentra¬ 
tion of the spreader gave better results. Ruth and Kelley 4 likewise 
observed that it was very difficult to wet certain areas of a tree, that 
differences in surfaces existed, and that the surfaces changed through¬ 
out the growing season. This change in surface, whether leaf or 
fruit, probably accounts for contradictory results obtained by dif¬ 
ferent workers using the same kind of spreader. Under these cir¬ 
cumstances it would be futile to conclude from laboratory tests that 
a substance would spread on all surfaces. 
In a search for better and more practical spreaders many substances 
and combinations of two or more materials were studied. As nega¬ 
tive results were obtained, many of them are not reported in the 
tables. The materials that aided best in producing a film over the 
surfaces tested may be divided into two classes, namely, the soaps 
and the substances containing water soluble or colloidal solutions 
of proteins. In general, the soaps required much higher concentra¬ 
tion than the soluble proteins to produce equal spreading on most of 
the surfaces tested. Contrary to Moore’s opinion that spreading of 
casein would not occur unless sufficient force was applied to penetrate 
the wax covering of the cabbage leaf, a good film was formed with 
most of the soluble protein materials, when sprayed to the drenching 
point. The force necessary depended upon ,the concentration of 
the protein, being greater for the lower concentrations and less at 
the higher concentrations. This indicates a flattening of the droplets 
by force until they cohere to form a continuous film instead of pene¬ 
trating the waxy surface. The same holds true for the waxy covering 
of the apple. 
* Ruth, W. A., and Kelley, V. W. recent advances in spraying. Unpublished data 1922. 
