54 



London purple was supposed to consist of an organic dye residue and 

 calcium arsenite, but work which the author has carried on shows that 

 it consists of an organic dye residue, calcium arsenite, and calcium 

 arsenate. 



While the relative quantities of the two last-mentioned substances 

 vary a great deal, the total amount of metallic arsenic is nearly the 

 same in all samples examined. 



According to the old way of examining London purple, a portion was 

 extracted with water and the soluble arsenious oxid determined in the 

 solution. Where this was low the sample was passed as good and was 

 used in spraying. Since it has been found, however, that arsenic oxid 

 is also present, this must also be determined in the soluble portion. 

 Proceeding in this way, it was found that whenever the soluble arsen- 

 ious oxid was low the soluble arsenic oxid was high, and vice versa, 

 so that in every sample examined the total amount of arsenic going 

 into solution was very high, much higher, in fact, than the maximum 

 limit of 4 per cent that has been previouslj' recognized. Following 

 are examples of three representative samples: 



It is a well-known fact that although London pui-ple has gone out 

 of use to a great extent noM' because of its scorching the foliage, it 

 has been used and is used in many cases with excellent results. The 

 only conclusion we can come to from the above facts i^s that many 

 plants, under certain conditions at any rate, can stand a vast amount 

 more of soluble arsenic than has been previou.sly supposed. Of course, 

 if this arsenic were present as the free acid it would undoubtedly kill 

 or defoliate the tree; but its being present, as it is in London purple, 

 as the calcium salts of arsenious and arsenic oxid evidently has a 

 strong modifying influence. 



Compounds of this class are also being studied by the Bureau of 

 Chemistry and Division of Entomology and, just as in the case of Paris 

 green, the cooperation of the variou.s States is absolutely indispensable 

 to the success of the work. 



The foregoing paper by ]\Ir. Hayward was read by the secretary 

 of the association. 



After the reading of these papers, they were opened for discussion. 

 Mr. Smith stated that he had taken a greater interest in these 



