REASONS FOR INVESTIGATION. 7 



purposes. These methods, with the reason for their adoption, are as 

 follows: 



In determining soluble arsenic it is evident that it would not be suf- 

 ficient to extract the green for only 24 hours with water, since in 

 samples containing free arsenious acid as such, all of the arsenic does 

 not go into solution in that length of time, and neither do samples that 

 are poorly made break up to any extent within twenty-four hours. 

 The author has found that it takes from five to ten days, according to 

 the amount present, for all the free arsenious oxid to go into solution. 

 It has also been found that badly made greens are broken up enough 

 during the course of ten days to give some idea of their instability and 

 that well-made greens are not broken up to any great extent during 

 that length of time. It has therefore been thought best to determine 

 the soluble arsenious oxid in Paris Greens by extracting one part of the 

 green with 1,000 parts of carbon dioxid-free water for ten days and 

 at the end of this time determining the arsenious oxid in an aliquot 

 portion of the filtrate. This method shows whether the green con- 

 tains a large quantity of free arsenious oxid or whether it is badly 

 made, but does not distinguish between the two. A method devised 

 by Avery and Beans, a however, allows us to approximately determine 

 the amount of free arsenious oxid present exclusive of that formed by 

 the decomposition of the green. Therefore, by using both methods 

 the chemist will be able to tell either the amount of free arsenious 

 oxid actually present in the green or the amount that is apt to be 

 present a short time after spraying. Both of these forms of soluble 

 arsenious oxid are undoubtedly injurious, although perhaps not 

 equally so. 



These two distinct types of soluble arsenious oxid in commercial 

 Paris Green have not been previously recognized, and furthermore 

 when 4 per cent was adopted as the maximum amount of soluble arseni- 

 ous oxid allowable in Paris Green the extraction with water was con- 

 tinued for a much shorter time, resulting in much lower figures for 

 soluble arsenious oxid. It would appear, therefore, that investiga- 

 tion along this line is needed 6 to determine the maximum amount of 

 soluble arsenious oxid, as found by our present methods of analysis, 

 that can be present in a Paris Green in both forms without danger of 

 scorching. This investigation is an attempt to answer the question 

 under the first condition, i. e., when the soluble arsenious oxid is 

 present in the free condition. It is hoped that in the near future 

 experiments may be made on Paris Greens of the second type. 



J. Amer. Chem. Soc., 23: 111. 



& Valuable work upon the effect of arsenic and arsenite on plants has been pub- 

 lished by Gillette, Wood worth, Bailey, Marlatt, and others, but not along the lines 

 followed in this experiment. 



