INSECTICIDES 475 



As there is always some danger of foliage injury from the use 

 of these homemade arsenic compounds, and as they cannot 

 be safely combined with the dilute lime-sulfur when used as a 

 summer spray, they are now rarely employed in commercial 

 orchard spraying. 



Paris Green 



Pure Paris green, 3 Cu(As02)2 • Cu(C2H302)2, is composed of 

 copper oxid CuO, acetic acid HC2H3O2 and arsenious oxid 

 AS2O3 chemically combined as copper-aceto-arsenite as fol- 

 lows : 



Copper oxid 31.29 per cent 



Arsenious oxid 58.65 per cent 



Acetic acid 10.06 per cent 



The commercial grades often contain impurities and vary 

 somewhat from the above. By the National Insecticide Law 

 of 1910 Paris green must contain at least fifty per cent of ar- 

 senious oxid, and must not contain arsenic in water soluble form 

 equivalent to more than three and one half per cent of arseni- 

 ous oxid. 



For many years Paris green has been the standard ars(mi(;al 

 insecticide for orchard use ; but owing to the danger of foliage 

 injury on stone fruits and even on pears and apples when used 

 freely, it has now been generally replaced by the safer and more 

 adhesive arsenate of lead. Furthermore, Paris green cannot 

 be safely combined with the dilute lime-sulfur when used as a 

 summer spray, nor can it be used in the self-boiled lime-sulfur 

 on peach. In spraying apples it is usually used at the rate of 

 eight ounces in 100 gallons of water. The danger of foliage 

 injury is greatly lessened by using Paris green in Bordeaux 

 mixture, or if applied in water by adding lime twice the bulk of 

 Paris green. 



London Purple 



London purple is an arsenite of lime obtained as a by-prod- 

 uct in the manufacture of aniline dyes. Its composition is 



