G15 



always retarded. As regards the alkaline powders, the anticrypto- 

 gamic action they derive from the insoluble copper which they contain 

 is nil. It is possible that dusting with an alkaline powder after spray- 

 ing with an acid cupric solution may lead to the action of the latter 

 being neutralised. There is a very simple method of determining in 

 which of these three classes a cupric dusting powder may be placed. 

 About } oz. of powder is put into a tall tumbler which is nearly filled 

 with water. The contents are stirred for about an hour with a rod 

 and then allowed to clear by settling. A large, bright iron nail is 

 put through a piece of cardboard which covers the mouth of the tumbler 

 so that a portion of the nail is submerged. With an acid powder 

 this portion will blacken, and the speed with which it does so will 

 depend on the degree of acidity ; a very rapidly formed, deep black 

 colour shows that there is a danger of scorching the leaves and also 

 perhaps the grapes. Neutral and alkaline powders do not act on the 

 iron. To differentiate between these, about | oz. of powder is placed 

 in a tumbler and the jet from a Seltzer siphon is directed into it until 

 nearly full. After some time, bicarbonate of copper is formed. After 

 stirring for about an hour a nail is placed in position as described 

 above and it will gradually turn brown with a neutral powder, an 

 alkaline powder producing no reaction. 



The base of most acid powders is talc or steatite, a natural product 

 composed of silicate of magnesia and obtainable in the form of a very 

 fine powder, which is soapy to the touch. This steatite is usually 

 impregnated with copper sulphate, though sometimes verdigris or 

 neutral acetate of copper is employed for the purpose. During the 

 process of impregnation, the impurities in the steatite cause reactions 

 which render the major part of the copper insoluble. These reactions 

 may continue after the powder is placed in bags. Old powders are 

 therefore less acid — ^and hence less rich in free copper sulphate — than 

 freshly manufactured ones. Neutral powders are produced by the 

 same means, but the impurities in the talc are present to a greater 

 extent, so that all the copper sulphate is rendered insoluble. It some- 

 times happens that the talc has simply been mixed with copper hydro- 

 carbonate or another insoluble copper compound. Such mixtures 

 cannot immediately yield soluble copper to rain water or dew. The 

 alkaline powders are based on finely sifted lime ; the copper is quite 

 insoluble in water and the greater part of it is present as black copper 

 oxide, wliich is one of the forms of copper least soluble in carbonic 

 acid. 



Semtchon (L.). L'invasion de Pyrales et la destruction des pontes. 



[The invasion of the vine tortrix and the destruction of its eggs.] 

 —Rev. Vitic, Paris, xliii, no. 1098, 15th July 1915, pp. 37^2. 



The damp weather of 1915 has been very favourable to the vine 

 moths, Ch/sia ambigueUa and Pohichrosis hotrana, and to the vine 

 tortrix, SparganrAhis pilleriana. The last-named has never before 

 been observed in such numbers in Aude and urgently needs control. 

 The crushing of the caterpillars is a very costly method. Insecticides 

 are not sufficiently efficacious, because this pest appears when the 

 young vine shoots are growing most vigorously and daily exposing 

 new tissues. In consequence, to be of real use, spraying would have 



