Large amounts of water soluble arsenic are liberated when sulfur-lime dry mix spray containing acid lead arsenate is exposed to the atmosphere in thin layers on glass plates. This is brought about by the calcium carbonate formed from the hydrated lime. Still greater percentages of soluble arsenic are formed when the Ca(OH)2 is entirely replaced by CaCO3 Apparently high humidity, intense sunlight and a temperature of 110°F., singly or combined, do not play any significant role in decomposing the PbHAsO4 but may cause arsenical injury to foliage indirectly by increasing the permeability of plant tissue to water soluble arsenic.