April, ’28] 
smith: speaders and spraying 
203 
the opposite side, that has not been sprayed. With calcium caseinate, 
especially, the spreading occurs at the instant the spray strikes and there 
is no secondary spreading; hence, in order to get complete coverage, it is 
necessary to spray a tree at least from opposite sides, if not from a 
number of different positions, the same as ordinarily is done. The intro¬ 
duction of a spreader also affords opportunity to accomplish other 
desirable improvements in the physical and chemical composition of 
spray mixtures and solutions, which in themselves are of much im¬ 
portance. 
The writer is not prepared to undertake at this time an extended 
discussion of the qualities and merits of the numerous substances 
that have been tested as spreaders; therefore, only certain phases of the 
subject are here considered. The thickness of the film-deposit, or the 
dry material that remains after the liquid film evaporates, is of much 
importance in choosing a spreader. In case of dormant spraying, for 
example, it usually is desirable to effect a comparatively thick coating of 
material on the bark, and the same applies, though perhaps in a more 
general way, to fruit and foliage sprays. Substances having very low 
surface tensions, such as saponin and soaps, are efficient in producing 
spreading and film formation, but the resultant film-deposit of spray 
material is so thin, at least in case of arsenate of lead, that there may be 
doubt as to its efficiency in giving protection to the sprayed surface. 
Caseinate gives a thicker and more durable film-deposit than do the 
above substances. Calcium caseinate possesses certain qualities not 
well understood, which cause a rapid fixation of the liquid film, and this 
gives promise that within certain limits we may be able to govern, 
according to various requirements, the thickness of the film-deposit. 
Compatibility with the various standard and proprietary insecticides 
and fungicides, as well as with spray waters of varying alkalinity, is a 
qualification that alone is sufficient to eliminate a number of spreaders 
that have been tried. Soaps, such as commonly are used with nicotine 
sprays, show a marked tendency to produce flocculation, precipitation 
and insoluble soaps, which deleteriously affect the physical and chemical 
composition of spray solutions and mixtures. These substances, and 
also sodium caseinate (casein dissolved with sodium hydroxide), when 
used with arsenical spray mixtures, tend to increase the amount of 
soluble arsenic in arsenical compounds and to lessen the stability of 
combined sprays. Calcium caseinate appears to exhibit none of these 
defects, so far as we have been able to determine at the present time. 
Miscible oils are good spreaders and possess some additional qualities 
