THE FIELD TESTING OF COPPER-SPRAY COATINGS. Ie) 
Treat similarly 5 c. c. portions of the washings from the leaf samples. Compare 
the color developed in these with the graded series. Take for a reading the number 
expressing milligrams of copper per 100 c. c. in the stock dilution that matches closest 
in color intensity. Simply multiplying this reading by 5 will then give a value in 
milligrams of copper per 100 grams fresh weight of leaf sample, a convenient unit for 
finally expressing the amount of copper in the spray coating. The results from the 
several samples may be compared and averaged. 
CONCLUSION. 
This field method of following the persistence of copper-containing 
sprays promises to be of service to pathological investigators, agri- 
cultural experts, and commercial growers along these lines: (1) To 
secure data showing the persistence of copper-containing sprays as 
it may be influenced by method of preparation, weathering, or 
other factors; (2) to determine the minimum and maximum limits 
of working safety zones, as measured by evenly distributed residues, 
effective for the practical control of specific diseases; (8). to secure 
prompt correction of faulty spraying practices, either in the prepa- 
ration of mixtures or in the times or modes of application, with a 
view to insuring more effective and economical protection of crops; 
and (4) to serve as a practical guide in timing new applications, 
especially after rainy periods. 
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