REPORT OF THE SOCIETY 75 



the result that he got some leaf injury. There is just a possibility that white 

 arsenic might be used in this type of dust on potatoes to good advantage. 

 Extreme care would have to be taken in having the same white arsenic from the 

 same source used every year, for white arsenic is one of our most variable pro- 

 ducts so far as its reactions go. 



Brown Copper Arsenic Dusts. 



This dust is made up of arsenic acid, crystal copper sulphate, burned lime 

 and water. The heat of the slaking lime is utilized to convert the arsenic acid, 

 into arsenate of lime and to cause the copper to be dehydrated and combined 

 as double basic sulphates. This dust is being sold entirely for apple woik this 

 season in the proportions of 18 pounds of crystal copper sulphate, 8 pounds of 

 arsenate of lime and the remainder, to make up 100 pounds, hydrated lime. 

 This dust is not so easy to grind or so fine as the Gieen Copper Arsenic dust, 

 which follows. 



Green Copper Arsenic Dust. 



This dust is the lowest priced of all dusting materials. It is made up of 

 white arsenic, crystal copper sulphate, burned lime and water. As in the last, 

 the heat of the slaking lime is utihzed, but the arsenic is caused to combine with 

 the copper, forming double copper calcium arsenite. This dust is made for the 

 potato in the formula of 9 per cent metallic copper and 5 per cent metallic ar- 

 senic, or the equivalent of 36 per cent of crystal copper sulphate and killing value 

 in arsenite form equal to 25 per cent of arsenate of lead. This dust is being sold 

 for less money than the average farmer can purchase equivalent values in crys- 

 tal copper sulplhate, arseiiat'e df lead and lime fot making up liquid Bordeaux 

 thus making dusting materials, for the first time, cheaper than equivalent, 

 materials for liquid spra!ying. 



The extreme friability of this type of dust makes it possible to pulverize 

 it so that over 98 per cent will pass a screen of 325 messes to the inch. The solu- 

 ble arsenic in the 9-5 Green potato dust can be made 0.11 and the soluble arsenic 

 in the 6-3 Green apple dust can be made 0.1 which is much lower than either 

 crop demands for safe.ty. 



I have endeavored in trhis papet to give a brief resume only of the points 

 that are now uppermost in combinations of cbpper, slilphur, arsenic and nico- 

 tine. 



