48b Journal of Agriculture, Victoria. [11 Aug., 1919. 



neutral verdet, whicli constitutes a coating so slight as to be scarcely 

 perceptible unless very closely examined Our investiga- 

 tions reveal a fact of considerable importance, and one which, so 

 far as we are aware, has not hitherto been mentioned in publica 

 tions dealing with the treatment of mildew: viz., that by simple 

 evaporation in air, of a dilute solution, sprayed on the leaves, the 

 neutral verdet is transformed into basic verdet (verdegrls), 

 insoluble, or at least sparingly soluble in water, so that washing, 

 even if very prolonged, does not remove it, but always leaves a 

 certain proportion of copper on the spiayed tissues. 

 In support, numerous experiments are described in detail. In one 

 series, three lots of vines (A B and C) were sprayed with \ per cent 

 neutral acetate. A wa3 allowed to dry, whilst B and C were submitted 

 to copious washings, corresponding to the action of heavy rain; respec 

 tively, twenty-four hours and six hours after spraying. Shoots from 

 the different plots were then analysed, when it was found that if the 

 proportion of copper present on the sheets irom plot A be represented 

 as 100 parts, those from plot B retained 81 parts, and those from plot C 

 61.5 parts of copper. In other words, even in the very unfavorable 

 case corresponding to a heavy fall of rain soon after sprayijig, the 

 copper removed was less than 40 per cent, of the total applied. 



In further experiments, the washing of the sprayed leaves was puj 

 posely so much exaggerated as to lead to the anticipation that all copper 

 would be removed; on analysis it was found that 12.5 per cent, still 

 remained. 



Field experiments on a large scale were also conducted; numerous 

 copper determinations, made towards vintage time, showed that of the 

 total copper applied when spraying, the proportion still remaining was 

 4.5 to 19 per cent, in the case of Bordeaux mixture; 3.3 to 22 per cent 

 for Copper Soda, and 8.8 to 31.9 per cent, with Neutral Acetate. 



An interesting controversy ensued, Guillon and Gouirand criticising 

 the conclusions of Chuard and Porchet. In reply the latter point out 

 that concentration has a considerable bearing on the result; neutral 

 acetate should be used in dihite sohition. If concentration be excessive, 

 it retards the decomposition into basic acetate and acetic acid — Guillon 

 and Gouirand used a fairly strong acetate solution, viz., 2 per cent 

 Fineness of spray is also of importance; large di'ops hinder rapid evapo 

 ration, the resultant crystals not decomposing readily, are liable to 

 removal by rain. 



Vermorel and Dan tony have contributed numerous articles to the 

 French viticultural press concerning the value of acetates, and in 

 particular of the neutral acetate Vermorel's well-known Boxiillit 

 eclair (Lightning Spray Mixture) consists mainly of neutral acetate, 

 one of the chief advantages claimed for it is instantaneous preparation, 

 it being merely necessary to stir the powder into water in the proper 

 proportions. 



The following extracts from an article by Vermorel and Dantony 

 may prove of interest.* After pointing out that soluble copper salts 

 nearly always damage foliage to some extent, and that most copper saltfs 

 present an acid reaction, they proceed to state — 



If neutral verdet be used in rainy or very moist weather, there 

 may be some slight leaf damage (scarcely ever of fruit) because the 



* T es Verdets et le Tournesol (Copper Acetates and Litmus). Vennorel and Dantony, Pei>ue de Viticnl- 

 Hire. 23rd .Tuly, 1914. 



