Bordeaux mixture in combination with arsenical sprays

Abstract

1. The interaction of Bordeaux mixture with lead arsenate and with calcium arsenate has been studied by an examination of the effects which are produced:(a) When hydrated lime is added to the arsenical compounds.(b) When copper sulphate is added to the arsenical compounds and hydrated lime.2. The nature of the interaction of calcium hydroxide and diplumbic hydrogen arsenate has been shown to be most complex and to result in the complete decomposition of part of the lead arsenate and th e formation of basic calcium arsenates.3. Support is not given to the view that calcium carbonate decomposes diplumbic hydrogen arsenate with the production of soluble arsenic compounds.4. When the lead arsenate, in water, is allowed to interact for long periods with excess of hydrated lime, the amount of basic calcium arsenates formed is such that large quantities of arsenic are brought into solution by the action of carbon dioxide.5. Under conditions when the calcium hydroxide is rapidly converted to the carbonate the amount of arsenic rendered soluble is slight.6. The conclusion is formed that in actual spraying there is a definite reduction of the risk of arsenical injury when hydrated lime is added to lead arsenate and to calcium arsenate.7. It is concluded that when the conditions are such that the addition of hydrated lime brings about a reduction of arsenical injury, the use of an “equal-lime” Bordeaux mixture containing an equivalent amount of calcium hydroxide will prove far more effective.