32 N. S. ENTOMOLOGICAL SOCIETY 



A COPPER DUST. 



By G. E. Sanders and A. Kelsall. 

 Introduction. 



During the summer of 1917 a mixture of powdered dehy- 

 drated copper sulphate was mixed with hydrated lime and tried 

 in liquid, in an attempt to find a method of making Bordeaux 

 mixture more rapidly than the "Quick time" formula already 

 published from this Laboratory. This mixture was found im- 

 practicable in a liquid on account of the combination curdling, 

 instead of forming a flocculent,blue precipitate. For some time 

 a bottle of the dry mixture remained in the Laboratory until 

 one day it was decided to try applying it as a dust. This was 

 tried on foliage in the green house at MacDonald College, P. 

 Q. and contrary to expectations it was found that a dust mix- 

 ture of this type containing as high as eight per cent of metallic 

 copper could be applied to foliage with safety, under the con- 

 ditions tried, thus showing the mixture to have some promise. 

 It was consequently decided to try this dust thoroughly dur- 

 ing the summer of 1918. 



According to most authorities on the subject one pound 

 of dust is equal in covering power to two gallons of liquid. In 

 making up the dust for the potato, to substitute the 4.4.40 

 liquid Bordeaux, it was made to contain five per cent of metallic 

 copper and two per cent of metallic arsenic, and it was planned 

 to use about 50 lbs. per acre. It was found that arsenate of 

 lime could be used with perfect safety in this dust, thus cut- 

 ting the insecticide cost in two as compared with arsenate of 

 lead. For the apple the formula of five per cent metallic cop- 

 per and two per cent metallic arsenic was halved. 



Manufacture. 



The 5-2 copper arsenic dust, five per cent metallic copper 

 and two per cent metallic arsenic was made for our experimental 

 work as follows: — 201bs.of crystal copper sulphate were roasted 

 until dry and white and then ground finely enough to pass a 

 screen of 100 meshes to one inch. Twelve and one half pounds 

 of white powder result from twenty pounds of blue crystals. 

 To the twelve and one half pounds of powdered de-hydrated 

 copper sulphate was added seven and one half pounds of dry 

 arsenate of lime (40% AS 2 5 ), and eighty pounds of hydrated 



