112 THE EEPORT OF THE No. 36 



former used 100 lbs. of the poison and reported that in his opinion it was quite as 

 satisfactory as Arsenate of Lead; the latter said that he was also pleased with the 

 results, hut did not think his tests sufficiently extensive to draw reliable conclu- 

 sions. 



My second test was against Potato Beetles. Mr. G. J. 'Spencer conducted this 

 for me. On one plot he used 1 lb. Arsenite of Zinc to 40 gallons Bordeaux mixture, 

 and on another 3 lbs. Arsenate of Lead to the same amount of Bordeaux. Both 

 poisons destroyed all the beetles, so that perfectly satisfactory results were obtained. 



In no case, whether combined with the lime-sulphur or with Bordeaux, did we 

 see any evidence of burning; moreover, the fungicidal value of the lime-sulphur did 

 not seem to have been lessened, because even the Snow apples that were sprayed 

 were almost entirely free from Scab, quite as free as those sprayed with Arsenate of 

 Lead and lime-sulphur. As the potatoes were early varieties and ripened before 

 there was any injury from Blight we cannot speak of the effect from this disease, 

 so destructive this year to late potatoes. 



The result of this year's experiments would therefore go to show that Arsenite 

 of Zinc may prove to be a very excellent and safe insecticide and may even super- 

 sede Arsenate of Lead, especially as, apart from its poisoning merits, it has several 

 advantages over the latter : — 



(1) It can be easily stored, being a powder, whereas Arsenate of Lead is a 

 paste and should not be allowed to freeze or dry out. 



(2) It takes less time to prepare for the tank, all that is necessary being to 

 mix up the desired amount in a pail with a little water and then pour it into the 

 tank, whereas Arsenate of Lead, being a paste, takes a good deal of stirring in 

 water to bring it into suspension. 



(3) It can be manufactured more cheaply than Arsenate of Lead; one pound 

 costing 20 cents, but each pound contains as much arsenious acid as a;bout three 

 pounds of Arsenate of Lead, and therefore is equivalent in killing power to that 

 amount. As Arsenate of Lead costs at least 10 cents a pound, an equal strength 

 of Arsenite of Zinc would cost only two-thirds this amount. 



(4) When used alone in water we found that it remained in suspension con- 

 siderably longer than Arsenate of Lead, this being due probably to the greater 

 fineness of the particles of which it is composed. AVhen added to lime-sulphur 

 this advantage was lost as it settled somewhat rapidly, thus indicating that con- 

 stant agitations would be necessary. In sticking qualities it is apparently slightly 

 inferior to Arsenate of Lead. 



Whether any chemical action takes place when it is added to lime-sulphur is 

 difficult to determine for certain, as in tests made by the chemists very little if any 

 change could be detected. 



Although this season's work has given me a very favorable opinion of Arsenite 

 of Zinc, I should not care to recommend anyone to use it except experimentally 

 for a year or two yet until we see how it will act under different conditions of 

 moisture and temperature. In conversation with some men from the United 

 States I was told that they had heard that the results there this year were not 

 satisfactory. Whether this be correct or not, it is probable that the insecticide has 

 been tested in many states and reports should soon begin to come in. These re- 

 ports ought to give us information as to the real value of Arsenite of Zinc. Should 

 it prove to be very satisfactory, there is little doubt that it would soon be manu- 

 factured in many parts of the United States and Canada, so that it could be pro- 

 cured without the present high cost for freight or express. 



