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Copper Fungicides

Published online by Cambridge University Press:  27 March 2009

Spencer Umfreville Pickering
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Extract

Investigations on the various products of the action of lime on copper sulphate, including ordinary Bordeaux mixture, led to the conclusion that the efficacy of such substances as fungicides depended on the proportion of copper in them which is rendered soluble by the carbon dioxide of the air, and, that if a deficiency of lime is used to start with, one of the lower basic sulphates of copper is obtained, from which carbon dioxide liberates a much larger proportion of copper than it does from the more highly basic sulphates present in ordinary Bordeaux mixture. The lowest basic sulphate is, owing to its physical condition, unsuitable for spraying purposes; but this is not so with the compound 10 CuO, SO3, obtained by adding lime-water to copper sulphate just short of alkalinity, and this substance has been put on the market under the name of Woburn Bordeaux Paste. In the absence of secondary reactions, carbon dioxide should convert one-tenth of the copper present in it into soluble copper sulphate, 2 (10 CuO, SO3) + 9 CO2 = 9 (2 CuO, CO2) + 2 CuSO4, whereas with ordinary Bordeaux mixture, any copper sulphate formed in this way, would be decomposed by the excess of lime present, and that ultimately remaining undecomposed would be very small in amount.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 4 , Issue 3 , January 1912 , pp. 273 - 281
Copyright
Copyright © Cambridge University Press 1912

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References

Page 273 note 1 Eleventh Report of the Woburn Experimental Fruit Farm, 1910; this Journal, III. 171Google Scholar; Trans. Chem. Soc. 1907, 1908, and 1909, 1411.

Page 274 note 1 This Journal, IV. 69 and 76.Google Scholar

Page 274 note 2 Throughout his paper, Gimingham speaks of the amount of copper remaining in solution in this and other similar cases, as nil. This simply means that it was less than that recognisable by the ordinary ferrocyanide test on which he relied. As will be shown below, the action of the liquids on iron would have proved that there was copper still in solution; and the ferrocyanide test would have done the same, if the liquids bad been concentrated by evaporation.

Page 275 note 1 Bulletin No. 135 of the University of Illinois Agricultural Experiment Station.

Page 276 note 1 In seven cases the copper equivalent of the iron dissolved in 3 hrs, varied from 3·5 to 4·7 per cent., with a mean of 4·2

Page 278 note 1 The total air used contained about twice as much carbon dioxide as that required by the lime, but the current was much too rapid for it all to be utilised.

Page 279 note 1 Some calcium sulphate is always retained by the basic sulphate in a state of combination (loc. cit. p. 49).

Page 273 note 2 It would, of course, owing to its physical condition, be much less effective as a spray fluid in practice.