THE FIELD TESTING OF COPPER-SPEAY COATIITGS. 9 



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 metliod 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; (3) to secure 

 prompt correction of faulty spraying practices, either in the prepa- 

 ration of mixtures or in the times or modes of apphcation, with a 

 view to insuring more effective and economical protection of crops; 

 and (4) to serve as a practical guide in timing new applications, 

 specially after rainy periods. 



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