25 



and analysis of tlie cyani(l(3 subsequently made showed tliat the par- 

 ticuhir brand purchased, Avhich should have contained 58 per cent, in 

 point of t'livX contained only 31.75 per cent. Tlie obvious lesson from 

 this ex])erience is that in the use of a chemical like this, when a defi- 

 nite i)roporti<)n is required, it will be necessary to have a chemical 

 examination made before there can be any certainty of its accomplish- 

 ing- the desired end. 



AR8ENITE OF COPPEK. 



In an article on Paris green in the last number of Insect Life (vol. 

 VII, pp. 408-411), attention was called to a new insecticide, viz, arsenite 

 of copper, prepared under my direction for experimental test. The 

 preparation of this substance occurred to me from a reasonable doubt 

 which I entertained as to whether the Paris green is not really more expen- 

 sive than is necessary for its use as an insecticide. Paris green is an 

 aceto-arsenite of copper, originally made for use as a pigment, and, hav- 

 ing been adopted by entomologists as an insecticide, is now being manu- 

 factured for this purjjose at the rate of 2,000 tons or more per annum. 

 The cost of this substance is very greatly increased by the addition of 

 acetic acid. The simple arsenite of copper, without the acetic acid, 

 can be had at about half the cost of aceto arsenite. It has also the 

 very decided advantage of coming in a very line pulverulent powder, 

 whereas the aceto-arsenite is in the form of rather coarse crystals, 

 which results in its rapid settling in water. In the article referred to 

 no tests with the arsenite of copper were recorded. Since that time, 

 however, a large quantity of arsenite of copper has been obtained, and 

 it has been tested on the foliage of various plants in conjunction with 

 parallel tests with Paris green. The strength used was 1 pound to 

 100 gallons of water and 1 pound to nearl}^ 200 (192) gallons. The 

 mixtures were made without the use of lime. On the foliage of cotton 

 and pear no injury resulted whatever with either strength or with 

 either mixture. The cotton experimented with was of vigorous growth 

 and the foliage very tender. The pear foliage, however, was mature 

 and hardy. In the case of peach both mixtures resulted in scalding 

 the foliage, the stronger proving very disastrous; but there was practi- 

 cally no difference in the arsenite of copper and the aceto arsenite. 

 The evidence so far, therefore, goes to indicate that as far as the action 

 on the foliage is concerned the arsenite of coi)i)er does not differ mate- 

 rially from ordinary Paris green. An analysis of the arsenite of copper 

 by the Department chemist shows that the arsenic in the arsenite of 

 copper is not soluble to any extent in water, and practically agrees in 

 this respect with aceto-arsenite, but is soluble in weak acetic acid, and 

 would therefore yield to vegetable acids and other luitural solvents 

 or to the juices of the digestive apparatus of insects. The ]KMcentage 

 of arsenic contained in the arsenite of copper is 40.23, which approxi- 

 mates that usually found in Paris green. 



