The investigation of the problem as given was taken up with the following 

 conclusins:- 



The injury caused by the Lead Arsenate alone, when srayed, was due to 

 the soluble arsenic, (As2 C>5 ) which was .36 of one percent and it can be in- 

 creased by passing Carbon-dioxide into the solution. 



When Lime-sulphur solution is treated with Lead Arsenate some Lead 

 ulphide is formed, the black precipitate, and Calcium arsenate set- 

 ting free some sulphur and hydrogen sulphide. The retarded injury caused 

 by the mixing of lead arsenate with lime-sulphur wash was due to the calcium 

 of the lime sulphur uniting with some of the soluble arsenic of the Lead Ar- 

 senate when they were mixed. Then by the action of the carbon dioxide of 

 tke air upon the calcium in combination, the arsenic (As2 Os ) was made sol- 

 uble after a period of almost a month. 



The Lime-sulphur solution when saturated with carbon-dioxide and then 

 sprayed gives no injury, but when the lime-sulphur solution is first treated 

 with lead-arsenate then saturated with carbon dioxide, it gives considerable 

 leaf injury caused by the action of the carbon-dioxide on the lime-sulphur so- 

 lution forming calcium carbonate and some hydrogen sulphide. The hydrogen 

 sulphide reacts with the lead arsenate forming lead sulphide (the black preci- 

 pitate) and some soluble arsenic, which does the injury. Lead Sulphide is 

 precipitated from water containing Lead Arsenate by passing hydrogen sul- 

 phide into it, although lead arsenate is insoluble in water. 



Lead arsenate used had .36 of one per cent of soluble Arsenic (As2 Os ), 

 when dissolved in distilled water; but when treated with water, which had 

 been saturated with Carbon-dioxide, it had .44 of one percent of soluble ar- 

 senic (As2 O5 ) showing that water containing carbon-dioxide, as hard waters, 

 have a greater dissolving power on Lead Arsenate. Therefore in making up 

 spraying solutions should use as soft a water as obtainable. The Lead Arsen- 

 ate and Lime-sulphur solution after being saturated with carbon-dioxide has 

 .66 of one per cent of soluble arsenic (As2 Os ) showing that the carbon- 

 dioxide pressure sprayers cannot be used with a mixture of Lime-sulphur and 

 lead arsenate, although it can be used to advantage with the Lime-sulphur 

 solution alone as the decomposition is very small and the free sulphur being 

 in such a fine condition would act as a fungicide which fact has been 

 demonstrated. Some soluble arsenic may also be produced by the action of 

 the carbon-dioxide on the calcium arsenate formed by the action of Lime-sul- 

 phur solution on the lead arsenate. The soluble arsenic is the damaging pro- 

 duct to the foliage so it is advisable to have the arsenic in as insoluble form as 

 possible. It is advisable, to avoid injury to foliage, in the use of any arsenical 

 spraying material, that may contain some free or soluble arsenic, to use some 

 milk of lime in excess, that is Calcium hydroxide solution, so as to take care of 

 any soluble arsenic present. This can also be used with the mixture of Lime- 

 sulphur and lead arsenate, especially when the Lead arsenate, which is to be 

 mixed with the dilute Lime-sulphur solution, is slightly acid. This treatment 

 of the Lead Arsenate before mixing with the dilute Lime-sulphur solution 

 would certainly be advisable, especially as a preventative of injury to foliage. 



