IxsEcT Killers. 343 



London purple is another substance which has been strongly 

 recommended as an insect killer. This is an arsenical mixture, a 

 waste product, being the refuse which remains after the manufact- 

 ure of aniline djes. Before its introduction as an insecticide it 

 had no commercial value, indeed the dye- makers were at consid- 

 erable expense and trouble in getting rid of it as it accumulated. 

 The arsenic, which is the active ingredient in it, is present in the 

 form of arsenious acid, and, as one might expect in a waste 

 product, in very variable proportions; sometimes it forms less 

 than twenty per cent, of the mixture, at others more than forty 

 per cent. Prof. Riley gives, as the result of an analysis by the 

 chemist in the department of agriculture, forty- three per cent. 

 while specimens, examined lately by myself, have not yielded 

 more than eighteen per cent. It is associated chiefly with lime 

 and coloring matter. The arsenic in this mixture is in a very fine 

 slate of division, and intimately mixed with the lime and other 

 materials, forming a very fine powder. It is much more soluble 

 than the Paris green, and hence more liable to scorch the foliage, 

 while its very variable strength makes it an uncertain compound 

 to trust to. For these reasons London purple is certainly far 

 inferior to Paris green for this purpose. 



Arsenic or arsenious acid has also been tried diluted with vari- 

 ous substances. An artificial mixture of arsenic and lime of 

 known strength, colored, could be supplied just as cheaply, and 

 would be more reliable than London purple, but, owing to its 

 solubility and caustic character, unless used very carefully it is 

 apt to destroy the tissues of the leaves, making them appear as if 

 burnt or scorched. 



Powdered hellebore, which is the powder of the root or rhizome 

 of veratrum album, is a poisonous substance which, iu most 

 instances, destroys caterpillar life very promptly, but there are 

 some insects much less sensitive to its effects than others, and for 

 these Paris green is required. Wherever hellebore will accom- 

 plish the desired purpose it should be used in preference to 

 stronger poisons. It is best applied mixed with water in the pro- 

 portion of one or two table-spoonfuls to a pailful of water, and 

 used with a whisk, as recommended for Paris green. Taken in 

 any quantity into the human system this powder produces very 



