370 MANUAL OF VEGETABLE-GARDEN INSECTS 



Copper oxid 31.29 per cent 



Arseiiious oxid r)(S.65 per cent 



Acetic acid 10. 00 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 50 per cent of 

 arsenious oxid, and must not contain arsenic in water-soluble 

 form equivalent to more than 3^ per cent of arsenious oxid. 



Paris green is most widely used for spraying potatoes and is 

 usually combined with bordeaux mixture. When used in 

 water, an equal weight of lime should be added to neutralize 

 any soluble arsenic present and thus prevent burning of the 

 foliage. For many purposes paris green is now largely re- 

 placed by arsenate of lead, which is less likely to burn the leaves 

 but is a little slower in its effect on the insects. 



Paris green is sometimes applied in the dry form and may 

 then be diluted with hydrated lime or land plaster. 



London purple. 



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

 in the manufacture of aniline dyes. Its composition is variable, 

 the arsenic content varying from 30 to 50 per cent. It is a finer 

 powder than paris green and, therefore, remains longer in sus- 

 pension in water. It is used in the same way as paris green, 

 but owing to the presence of much soluble arsenic, is likely to 

 cause foliage injury. This can be averted by the use of lime as 

 advised under paris green. London purple is now little used as 

 an insecticide. 



Arsenate of lead. 



Arsenate of lead has practically replaced paris green for 

 spraying orchard trees and its use on vegetable crops is rapidly 

 becoming more widespread. It contains less soluble arsenic 



