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The lime sulphur-calcium arsenate spray

Published online by Cambridge University Press:  27 March 2009

W. Goodwin  and
H. Martin
W. Goodwin
Affiliation:
Research Department, South-Eastern Agricultural College, Wye, Kent.
H. Martin
Affiliation:
Research Department, South-Eastern Agricultural College, Wye, Kent.
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Extract

The calcium arsenate-lime-lime sulphur spray has been studied in the laboratory and from the results so obtained it is inferred

(1) That the formation of a stable tricalcium arsenate by precipitation from aqueous solution is improbable. The interaction of calcium hydroxide and dicalcium arsenate results in the formation of a continuous series of basic calcium arsenates which are hydrolysed in aqueous suspension.

(2) That through the formation of such basic calcium arsenates the addition of lime to dicalcium arsenate reduces the amount of arsenic in solution. This reduction is temporary and on exposure to atmospheric carbon dioxide the original solubility of the dicalcium arsenate is restored. The concentration of soluble arsenic in the dicalcium arsenatelime spray will not be as great as in the dicalcium arsenate spray and the risk of spray injury with the dicalcium arsenate spray is therefore reduced when lime is added.

(3) The concentration of soluble arsenic in the dicalcium arsenate and lime spray is reduced by the admixture of lime sulphur with a corresponding reduction of the risk of foliage injury.

(4) The precipitation of sulphur from the calcium polysulphides of the lime sulphur is unaffected by the addition of dicalcium arsenate. The addition of lime may result in a diminution of the amount of sulphur so precipitated but such a reaction is dependent on the rate of carbonation of the free lime on the leaf surface. The fungicidal activity due to the calcium polysulphides is therefore unaffected by the addition of dicalcium arsenate but may be adversely influenced if excess of calcium hydroxide be present.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 16 , Issue 4 , October 1926 , pp. 596 - 606
Copyright
Copyright © Cambridge University Press 1926

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References

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