Some Paris Greens Analyzed in igo§. 



No. 



1 

 2 

 3 



4 

 5 

 6 



Moisture 

 100°C 



1.29 

 .99 

 1.25 

 1.26 

 1.29 

 1.41 



Sand 



.11 

 .23 

 .26 

 .15 

 .71 

 .12 



Total 



arsenious 



acid 



Ab 2 3 



56.55 



56.91 



56.8 



56.12 



56.01 



56.33 



Acetic 

 acid by- 

 difference 



11.03 



10.12 

 10.73 

 11.72 

 11.19 

 10.05 



Soluble 

 arsenious 

 acid 

 AS2O3 



2.36 

 2.73 

 2.11 

 2.85 

 2.73 

 4.35 



These greens are all as satisfactory as we can expect the commercial 

 article ever to be. Probably No. 6 contains somewhat more sodium sul- 

 phate than there is any need for, and is also somewhat high in free ar- 

 senious acid ; otherwise there are none of them but could be highly 

 recommended for spraying purposes. 



London Purple. 







London purple is prepared by boiling a purple residue from the dye 

 industry, containing free arsenious acid, with slaked lime. In this way 

 calcium arsenite and calcium arsenate are formed, and these are the poi- 

 sonous compounds of this insecticide. As the dye residue has accumu- 

 lated some dirt during the process of manufacture, a sandy substance will 

 always be present in the London purple. It will thus be seen that London 

 purple consists of calcium arsenite, calcium arsenate, a dye residue, and 

 small amounts of sand and moisture. In case not enough lime is added 

 to the dye residue or the boiling is not continued long enough, varying 

 quantities of the arsenious acid will be left in the free condition, and thus 

 in a form which will scorch the foliage to which it may be applied. 



According to Haywood,* about one-third of London purple is made 

 up of the dye residue, sand, and moisture, and that it contains from 31 

 to 51 per cent, of total arsenic, figured as arsenious oxide; whereas Paris 

 green contains the equivalent of about 56 per cent, of the arsenious oxide. 

 The value of these two insecticides will thus be in proportion to these 

 figures. However, one other point must be considered in valuing this 

 substance, that is, its effect on foliage. According to Haywood, a very 

 much larger amount of the arsenic of London purple is soluble in water 



* U.S. Department of Agriculture, Bureau of Chemistry. Bull. No. 68. 



