PARIS GREEN SPRAYING EXPERIMENTS. 



REASONS FOR THE INVESTIGATION. 



These experiments were undertaken to show how much soluble 

 arsenious oxid may be present in samples of Paris Green used for 

 spraying purposes without injury to the foliage. As is well known, 

 Paris Green is composed of copper oxid, acetic acid, and arsenious 

 oxid, combined as copper-aceto-arsenite in the following proportions: 



Per cent. 



Copper oxid 31. 29 



Arsenious oxid 58. 65 



Aceticacid 10. 06 



Since this substance is always sold upon the market as a commercial 

 rather than a chemically pure article, small amounts of impurities are 

 always present. Among these may be mentioned sand, sodium sul- 

 phate, and arsenious oxid, the last of which is not combined as it should 

 be with the other constituents, but is present in the free state. It is 

 to this impurity of Paris Green that the scorching properties are 

 usually ascribed. California has passed a law limiting the amount of 

 free arsenious oxid in Paris Green to 4 per cent, while New York's law 

 limits the amount to 3.5 per cent. In the other States, where there 

 are no laws governing the matter, the entomologists usually consider 

 4 per cent of free arsenious oxid to be the maximum amount allowable 

 in Paris Green used for spraying. 



It does not seem to have been generally recognized by entomologists a 

 and chemists that there may be three conditions of Paris Green which 

 will cause a scorching of the foliage. 



(1) As indicated above, there may be a certain amount of arsenious 

 oxid in Paris Green over and above that combined with the other con- 



Marlatt in two articles (Insect Life, vol. vii, July, 1895, pp. 408-411, and bulletin 

 No. 6, Division of Entomology, September, 1896, pp. 30-35) has recognized the first 

 and third conditions of Paris Green that may give rise to a scorching of the foliage, 

 but not the second condition. 



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