174 



Cliemical tests made in connection with spraying experiments ^vitli 

 solutions containing- white arsenic, London purple, or Paris green, and 

 with Bordeaux mixture revealed the tact that "in no case was injury 

 noticeable where soluble arsenic was absent, but in all cases it waspni- 

 portional to the amount of soluble arsenic." 



Seeing in this experiment the insolubility of the arsenites in Bordeaux mixture 

 and the consequent exemption of foliage from injury, and kuo wing that London jmrple 

 "was, in the main, an arsenite of calcium, hcing juoduced by the decomposititm of 

 rosauiline arsenite by calcium hydrate (lime in solution), it was at once plain, from 

 a chemical point of view, that lime would render the soluble portion of the arsenites 

 in.soluble in water, and thus render foliage free fiom injury from them. Variims 

 mixtures of an equal weight of pure lime (CaU) and white arsenic, London purple, 

 and Paris green, separately in water, were made to test this point. Some of the 

 mixtures contained as much as 4 pounds of arsenite in 100 gallons, but in only a few 

 cases was so much as a trace of solul»lc arsenic found when tested by sulphureTed 

 hydrogen. [The results of the application of these mixtures to foliage are tabulated.] 

 In every case where there was solubh- arsenic there was also ''burning" of foliage, 

 and this in all cases was iu direct proportion to the anutuut of solulde arsenic. 

 "Where there was no arsenic in solution there was no burning of leaves except in 

 one case, where white arsenic and lime had been standing only 24 hours. 



Another table shows the amount of soluble arsenit* c(mi])ounds found in 

 1 and lOOgallonsof arsenical mixtures, 1. .">.."», 7, and L't bours.and 10 days 

 after mixing, and tbc cntiic absence of snch compounds wlu-n linic was 

 present. 



AVhite arsenic, it will be seen, dissolves very slowly, requiring more than 10 days 

 for complete solution, even iu a largt> volume of water and at summer temperature, 

 while the soluble ])()rtion of Loudon pur])le goes into solution luactieally at cmce; 

 and the same is ajiproximately true of Paris green. • • » The beiietieial effect 

 of lime in the London purple mixture is due to its decomposing .ution upon the 

 rosauiline arsenite by which insoluble arsenite of lime is fornx-d. This change 

 takes place in a short time, as will be .seen from the loss of color of the mixture. 

 Double and triple weights of lime to Ixuidon ])urple were experimented with, 

 thinking it might require these amounts to eflect the decomposition, but an equal 

 weight was found to be ample. 



The beneficial cftect of lime in Paris green and white arsenic mixtures is also due 

 to the formation of the insoluble arsenite of lime. Kqual weights of lime to Paris 

 green and white arsenic each were found xutlicient in all cases, and no more than 

 this, even of the commercial article, need be added toParisgreen. But to be on the 

 safe side, I think it best to add 2 pounds commercial lime (C'aO) to 1 pound white 

 arsenic. One pound white arsenic ( As.Ot) requires approximately O.So pounds of lime 

 (CaO)to satisfy the reaction iu the production of the insoluble arsenite, but slight 

 excess of lime <loes not seem to do any harm — certainly far less than an excess of 

 arsenic. 



A very cheap insecticide. h;iving the s;ime inseeticidal ]n-oiierties as London pur- 

 ple, can be easily made by boiling together for one half hour, in 2 to 5 gallons i>f 

 water, 1 pound eonunerei.il white arsenic and 2 pounds <'onunereial lime, and diluting 

 to reijuired vcdume, say 100 gallons. 



Other cxp«'rinu^nts showed — 



(1) That Bordeaux mixture prevent-; tlu' -^oluliilit v of iIh' .irseuiti s :nul tlu ir 

 injiiry to foliage by virtue of its lime. 



