14 



ARSENITES. 



Of the numerous substances now in use, probably none are more 

 generally useful than the Arsenites, Paris green and London purple. 

 There is still some difference of opinion among entomologists as 

 to the relative merits of these two poisons, and it is quite probable 

 that each has its advantages over the other, one being better in 

 some cases while the other is best in other cases. I have experi- 

 mented somewhat for several years with both, and find that Lon- 

 don purple is on the whole better than Paris green for most pur- 

 poses, since it is cheaper and quite as effective. These may be 

 used as dry powders diluted with plaster, flour or some similar 

 material, but generally thev are more useful when used with water 

 sprinkler or sprayed on the plants or trees. The fact needs to be 

 kept in mind that no solution can be obtained by putting either of 

 the substances into water, only a mixture, and that this may be 

 uniform, not too weak to kill the insectsat one time, and so strong 

 as to destroy the foliage at another, it must be frequently stirred, 

 else the poison settles at the bottom of the vessel containing the 

 mixture. As to strength of the mixture, this will vary somewhat 

 with circumstances, but most experimenters agree that a mixture of 

 one pound of London purple and two hundred gallons of water is 

 strong enough for all ordinary purposes and not so strong that it 

 destroys or even greatly injures the foliage. Of course a small 

 quantity could be made in the same proportion, that is, an ounce 

 of purple to twelve gallons of water. Some would use a stronger 

 mixture than this, but probably it would rarely be advisable to use 

 more than one ounce in nine gallons of water. If a second spray- 

 ing is necessary it should be made with a weaker mixture, that is, 

 one ounce of London purple may be diluted with fifteen or twenty 

 gallons of water. Paris green is heavier than London purple and 

 stronger, containing about ten per cent, more arsenic, but is used in 

 equal bulk. Since the latter is lighter, much more arsenic would 

 be furnished the mixture than the diflference indicated would give. 

 Mixtures as strong as one pound of poison to one hundred gal- 

 lons of water have been used without injury to foliage, but at 

 other times very extensive damage to foliage has followed. Ac- 

 cording to Prof. A. J. Cook more damage to foliage results from 

 using the poisons late in the season than if used earlier, and " used 

 just before a rain are more harmful than during a drought." 

 Various experiments show that very little of the poison from 



