Materials and Formulas. 121 



Cu 3 (AsO 3 ) 2 . "This compound is to be had by adding an 

 aqueous solution of arsenic trioxide to an ammonia-copper sul- 

 phate solution ; this latter solution is prepared by adding am- 

 monia to a solution of copper sulphate until the precipitate 

 which is at first formed dissolves." 1 During 1895, the writer 

 tested this arsenite, and the results showed that its value in 

 destroying the codlin-moth is far inferior to that of Paris 

 green, while its fungicidal action is probably greater than that 

 of any other compound of arsenic and copper. The United 

 States Department of Agriculture conducted a similar work 

 during the year, but a full account has not yet been published. 



Paris Green; Schweinfurth' s Green; Emerald Green; Mitis 

 Green; French Green; Ac eto-ar senile of Copper ; (CuOAs 2 O 3 ) 3 

 Cu(C 2 H 3 O 9 ) 2 . Paris green may be prepared by making a boil- 

 ing solution of w r hite arsenic in one vessel, and a similar one 

 of acetate of copper (verdigris) in another. These two boiling 

 solutions are then combined, and Paris green is precipitated. 

 It appears as a more or less fine powder, having a beautiful 

 clear green color. It is practically insoluble in water, but dis- 

 solves readily in ammonia. It is for this reason that ammonia 

 forms such an excellent test for determining the purity of the 

 powder ; all sediment which the ammonia will not dissolve may 

 be considered as foreign matter. 



Ehrmann has given the composition of pure Paris green to 

 be as follows : a 



Copper oxide 31.29 



Arsenious acid 58.65 



Acetic acid 10.06 



Most samples, even of the purest grades, show some variations 

 from the above. 



Since very nearly all the arsenic found in Paris green is prac- 

 tically insoluble in water, it is true that this poison is the safest 

 insecticide now in general use. It will, nevertheless, injure 

 foliage, sometimes to a serious extent, if several applications 

 are made. The foliage of the stone fruits is particularly sus- 

 ceptible to this action, although even the apple will suffer. The 



* Shepard, " Elements of Chemistry." 1885, 245. 



2 Cited by Boss, Ala. Agric. Exp. Sta. 1894, August, Bull. 58, 5. 



