11 



Among the most important Paris green substitutes which contain 

 large quantities of arsenic are the various "arsenoids." All of these 

 insecticides are advertised as containing no leaf-scorching materials, but 

 analyses by Haywood* and Colbyf show that some of them are not by 

 any means free of soluble forms of arsenic. The gray and white arsenoids 

 are especially bad in this respect. The former is reported as containing 

 arsenic equivalent to 35 per cent, of arsenious oxide, fully one-third of 

 which is soluble in water;, while the latter has the equivalent of over 25 

 per cent, of the oxide, all of which is in a soluble form, and is, conse- 

 quently, sure to burn the foliage. 



The green arsenoid, copper arsenite, is reported as being as rich in 

 arsenic as Paris green, and does not contain an excessive amount in the 

 soluble condition. Pink arsenoid, or lead arsenite, while poorer in ar- 

 senic, is a safe insecticide in that very little of it is in a form that will 

 scorch the leaf. 



Bowker's Disprene and Swift's Arsenate of Lead are convenient 

 substances, and are among the safest forms of insecticides. The chief 

 advantages of the lead compounds are that they may be applied to all 

 kinds of foliage with less danger of injury than is the case with Paris 

 green, and, because of this fine state of division, they cling to the foliage 

 better, and remain in suspension in water for a longer time. 



Of the lead compounds, the arsenate is most used. In the pure 

 form, it contains arsenic equivalent to about 37 per cent, of arsenious 

 oxide, but in the condition in which it is placed on the market, the arsenic 

 content will be lower. According to an analysis made by Haywood, the 

 Swift's Arsenate of Lead contains only 25.62 per cent, of arsenic oxide 

 and 13 per cent, of organic matter. The organic substance consists of 

 dextrose and dextrin, and are apparently used to make the material stick 

 to the foliage. Colby states that in the form of paste this insecticide 

 contains only 12 per cent, of arsenic oxide and 43 per cent, of water. 

 Consequently, proportionately larger quantities of this substance will 

 have to be used than with Paris green. 



Home Made Arsenicals. 



There is no good reason why farmers, gardeners, and fruit growers 

 should not prepare the arsenical poisons they require just as they do the 

 Bordeaux and lime-sulphur mixture. The work involved in their pre- 

 paration is no more difficult, and when properly made they are fully as 

 efficient, and, possibly, safer than the best Paris green. 



Arsenate of Lead. The formulae for the preparation of this com- 

 pound vary slightly ; but in the following is the one given by the United 



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

 t California Agri. Experiment Station Bull. No. 151 



