72 
Journal of Agricultural Research 
Vol. XXXI, No. 1 
The present investigation was undertaken (1) to make a study of 
the known spreader materials and to search for others that may be 
more practical; (2) to correlate the surface-tension values of various 
materials with their spreading properties, and to learn more regard¬ 
ing the fundamental causes of spreading; and (3) to devise a labora¬ 
tory method whereby the approximate spreading properties of a 
substance may be estimated. 
REVIEW OF LITERATURE 
Previous investigations on the spreading properties of different 
substances consider a wide variety of materials. A very complete 
bibliography of the literature is given by Moore (7) 3 in his general 
discussion of the subject, and the review will not be repeated here. 
Summarized briefly, previous investigations have shown that various 
colloidal substances are most effective in modifying the spray mix¬ 
ture to make it spread over various surfaces and form a continuous 
film on the objects sprayed. Among those colloids, casein, soap, 
glue, saponin, and flour have been found adaptable under certain 
conditions. Other organic materials such as creosote, eugenal, and 
crcsylic acid are reported as having spreading properties on waxy 
surfaces, but their high cost and other objectionable features make 
them impracticable for use. 
The theory of spreading as applied to spray materials is presented 
in recent publications by Cooper and Nutt all (. 1 ) and by Moore 
(7). They elaborate upon the principles of wetting or spreading as 
first established by Quincke (£) in 1877. In a study of the capillary 
rise of liquids in tubes of different materials the latter formulated 
the conditions necessary for wetting or spreading to occur. These 
conditions as applied to spreading provided that in order to state 
definitely whether a liquid will wet or spread on a solid (or another 
liquid) it is necessary to know the values for the surface tension of 
the liquid and of the solid and the interfacial tension of the liquid 
to the solid. Spreading of a certain liquid or spreader solution 
would then occur if the surface tension of the solid or surface sprayed 
is greater than the sum of the surface tension of the liquid and the 
interfacial tension of the liquid to the solid. The magnitude of the 
inequality would indicate good or poor spreading of the liquid on 
the solid.' Since, however, the surface tension of the solid—if a 
solid has surface tension—is indeterminate, it would be impossible to 
obtain the actual values necessary to ascertain whether a substance 
would be a good spreader for a specific surface, as, for instance, the 
apple leaf or fruit. If approximate values could be obtained by 
substituting a liquid for the solid, as, for example, an oil for the waxy 
surface of fruit or leaf, the probable spreading properties of a given 
substance might be estimated. This was accomplished successfully 
by Cooper and Nutt all 0 ) in their evaluation of the wetting power 
of various stock dips. Reference will be made to this procedure 
later. 
From the preceding it is apparent that any spray solution to spread 
well should have both a low surface tension and a low interracial 
tension to the solid or surface sprayed, as the sum of these values 
must be less than the surface tension of the surface sprayed. If a 
3 Reference is made by numbers (italic) to “ Literature cited," p. 81 
