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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
velopment of acidity the spreading properties were destroyed. Neutral¬ 
ization by lime or other alkali restores its spreading propreties. Fresh 
milk normally is slightly acid, and under favorable temperature con¬ 
ditions rapidly develops higher acidity. Under comparatively low acid 
concentration the milk proteins are partially coagulated, thus destroying 
the spreading properties of the milk. By adding an excess of an alkali 
the proteins are again brought into colloidal solution and functions as a 
spreader. The commercial calcium caseinate is simply a mixture of 
hydrated lime and casein that has been precipitated from milk by the 
addition of a small amount of acid. When water is added to the mix¬ 
ture the calcium hydroxide brings the casein into colloidal solution 
which acts as a spreader. 
The amount of milk that should be used to give good spreading of a 
certain spray depends upon the kind and the age of the surface to be 
covered. Manufacturers of casein spreaders recommend the minimum 
amount that will be most satisfactory -under most conditions. This is 
oftentimes in excess and therefore a waste. Laboratory observations in¬ 
dicate that 3 quarts of skim milk or 7 ounces of skim milk powder to 
100 gallons of spray is an average amount, and about half that amount 
the minimum that should be used. Two to eight ounces of hydrated 
lime, depending upon the spray and the age of the milk, should be added 
to the latter. For example, 2 ounces is sufficient for fresh milk as a 
spreader for lead arsenate, while 8 ounces should be used with sour milk 
or with lead arsenate—lime sulfur combination spray. The milk is then 
introduced into the spray tank nearly filled with water. Finally the 
spray material itself is added. 
Leaves sprayed in the laboratory with lead arsenate and determina¬ 
tions made for the amount of arsenic that adhered showed no differ¬ 
ences between milk or milk powder used as a spreader and calcium casein¬ 
ate. Although it is generally recognized that calcium caseinate im¬ 
proves the spreading of various sprays, its use is limited on account of 
the high cost of the commercial product. Skim milk or skim milk 
powder will give equally good spreading if used in proper amounts, and 
may be obtained for less than one-third the cost of calcium caseinate. 
