258 State Horticultural Society. 



The usual method of preparing dust containing copper seems to 

 have been to slack the lime with a strong solution of copper sulphate. 

 When made on a small scale the resulting powder contains more or less 

 of green and blue copper compounds mixed with much of a dark brown 

 compound. The former are probably basic sulphates of copper, or of 

 copper and calcium (lime), and the latter a hydrated copper oxide, 

 formed by the action of the steam in the slacking process. When made 

 on a large scale most of the copper appears at the end in the oxide con- 

 dition, and a not inconsiderable quantity of the mixture is too coarse 

 grained to stick very well to the non-resisting leaves. 



While this oxide condition of the copper undoubtedly has some 

 fungicidal value, the opinion of experimenters seems to be that its 

 value is not at all equal to the value of the copper compound contained 

 in a properly prepared liquid Bordeaux mixture. The dry mixture here 

 proposed is the same that exists on the leaf after the water of the liquid 

 mixture has evaporated, except that there is present more lime relative 

 to the copper and less calcium carbonate. As soon as the powder gets 

 wet, calcium carbonate begins to form, of course. 



Whether or not this pOAvder when applied to the leaf wet with dew 

 or rain will prove as effective as the liquid Bordeaux mixture, only ex- 

 periment will show. It seems to have the requisite properties, chemically 

 speaking, namely, hydroxide condition of the copper and the necessary 

 excess of lime to prevent injury to the lea\'es, at the same time ex- 

 posing fungus spores already upon the leaf or which may fall upon 

 it afterwards to the toxic action of the copper. It being so extremely 

 finely divided it seems possible to cover the wet leaf surface as 

 effectually as when water is used as a carrier of the toxic agent. The 

 subsequent solvent action of atmospheric water and substances pro- 

 duced by the leaves and germinating spores are very likely the sam-i 

 with either material. 



In a bulletin to be issued by the Horticultural department at the 

 close of this season the results of practical tests with the powder will 

 be presented. If any one tries it, we shall be obliged if he will report 

 the results to us and tell us exactly how he prepared it, the number of 

 pounds of blue-stone, quick-lime and slacked lime he used as well as the 

 appearance of his mixture and how he applied it to the trees. 



The following remarks iipon powder spraying mixtures were 

 furnished by Professor Whitten of the department of horticulture: 



In the past few years a number of fruit growers in Missouri 

 have become interested in using dry sprays instead of the liquid 

 spraying mixtures that have formerly been popular. This interest 

 has been aroused on account of the fact that dry fungicides and in- 



