INSECTICIDES, PREVENTIVES, AND MACHINERY. 435 



This is due entirely to the fact that the water appHed to the leaves 

 becomes rapidly warmed up by the sun before evaporating, and 

 meanwhile dissolves every particle of soluble arsenic, bringing it 

 into direct contact with the vegetable surface upon which it rests. 



In London purple we have a decidedly smaller percentage of 

 arsenic, as will be seen by the following analysis : 



More of the arsenic is soluble here, which explains why London 

 purple is more apt to burn foliage than Paris green. Both the 

 insecticides just mentioned can be made entirely harmless to 

 foliage by adding weight for weight of caustic lime when mixing. 

 That is to say, in preparing the poison for use, take one pound 

 of Paris green or of London purple and one pound of quick- 

 lime ; add water enough to slake the lime, and mix thoroughly 

 while hot, so as to incorporate lime and poison completely. This 

 will fix with the lime every particle of the soluble arsenic con- 

 tained in the mixture, and it can then be diluted with water and 

 applied at almost any reasonable strength without much danger 

 of injury to even the most tender foliage. 



Paris green, containing the greatest percentage of arsenic, will 

 go furthest for insecticide purposes, and for most insects will be 

 effective when applied in liquid form at the rate of one pound in 

 two hundred gallons of water. Used against the plum curculio, 

 or against the codling-moth, one pound in one hundred and 

 seventy-five gallons is more effective. Used against the potato- 

 beetle, one pound in one hundred gallons is most satisfactory. 

 Used in a dry condition, the Paris green may be applied without 

 any danger of injury, provided the application be made in a very 

 fine dust. It can be mixed with plaster of Paris, flour, or air- 

 slaked lime, and, practically, one pound of Paris green in one 

 hundred pounds of lime or plaster makes a good mixture, effec- 

 tive for insects of almost all kinds and harmless to plants. There 



Per Cent. 



Moisture 



Arsenious oxide (AsgOg) .... 



Lime (CaO) 



Iron and alumina (FeaOa-r-AlaOs) 



Sulphuric acid (SO3) 



Dye, by difference 



3-27 

 41.44 

 24.32 



3-37 

 •31 

 27.29 



100.00 



