35 



Paris green, ordinary, is a rather coarse crystal, and settles very 

 rapidly in water solution. London purple is pulverulent, and settles 

 slowly. The lead arsenites and arsenates are precipitates, very pulveru- 

 lent, and settle much more slowly than even London purple, and in this 

 category also comes arsenite of copper, which is quite as satisfactory 

 in this respect as the lead poisons. The attempt to pulverize Paris 

 green was only partially successful. The powder was noticeably finer 

 than the ordinary product, but still settled very rapidly in water. The 

 fineness of division of the poison, as indicated in the foregoing experi- 

 ment, has an effect also in making it more poisonous to plants, but this 

 may be overcome by the use of lime, and it will probably prove that a 

 less amount of the more finely divided poison will accomplish as much 

 as a greater amount of coarser powder. 



The cost of these arsenicals varies with the market price of the con- 

 stituent elements, as bluestone, arsenic, lead, etc. The price of Paris 

 green ranges pretty close to 20 cents per pound. Arsenite of copper 

 or Scheele's green can be made for 10 cents per pound, and the arsenite 

 of lead (pink arsenite) prepared for our use can be made for about 8 

 cents per pound. 



Conclusion. — Results of experiments with these arsenicals during the 

 past few years have demonstrated to the satisfaction of the writer 

 the value of the simple arsenite of copper, and the experiments of the 

 present year also show the very considerable value of the arsenite of 

 lead. Both have a very decided advantage in their more flue divi- 

 sion, which render their use much more safe than an insecticide which 

 rapidly settles to the bottom of the tank, resulting in likelihood of great 

 inequality in strength as sprayed on the trees. Both of these arsenicals 

 may be obtained at about one-half cost of Paris green, or approximately 

 the cost of London purple, and are both of them far superior to London 

 purple in effectiveness and in safety when applied to foliage. 



Half the cost of Paris green or aceto-arsenite of copper, as has been 

 previously pointed out, comes in making it more suitable for a pigment, 

 its original market use, and this adds nothing to its value against 

 insects. I think the time has come when we should abandon its use 

 as an insecticide and substitute for it Scheele's green. Tbis arsenical 

 will be manufactured in any quantity by the Adler Color and Chemical 

 Works, of New York City, and as there is no secret about its compo- 

 sition it can also be made by any firm working in such material. 



Arsenite of lead is a most promising insecticide. The only objection 

 to it now is the fact that it may be made in several different forms hav- 

 ing varying percentages of arsenious oxide. Further work with this 

 substance is now being conducted, which, it is hoped, will demonstrate 

 a method of producing it even more cheaply than that now employed 

 and at the same time give a guaranty of uniformity in composition. 

 It may be colored, as in the sample exhibited, to prevent its being mis- 

 taken for harmless substances. 



