INSECTICIDES 



13 



is often in a more soluble form, and consequently 

 London purple is more likely to injure foliage than 

 Paris green, unless lime is added. It is a finer 

 powder than the green, and remains in suspension in 

 water longer. It is also cheaper. Before using, the 

 soluble arsenic should be made insoluble by the addi- 

 tion of lime water. One of the best ways to do this is 

 to add three-fourths of a pound of lime to a pound of 

 London purple, and thoroughly mix them in a gallon 

 of hot water, allowing the mixture to stand two hours 

 and keeping it hot during this time if it can be con- 

 veniently done. In this way the soluble arsenic will 

 be rendered insoluble, and the London purple may be 

 used at the rate of 4 or 5 ounces to a barrel of water. 

 Or the London purple may be added to the water as 

 usual, and about 2 gallons of fresh milk of lime (made 

 by slaking lime in water) strained into the barrel. 

 If allowed to stand an hour, all the soluble arsenic is 

 more likely to be rendered insoluble than if used at 

 once. After London purple has been thus treated 

 w4th lime it can safely be applied to tender foliage at 

 a strength of 4 ounces to 50 gallons of water. Both 

 London purple and Paris green may be added to the 

 Bordeaux mixture (4 ounces poison to 50 gallons mix- 

 ture), as described more fully elsewhere, and then 

 the treatment with lime is not necessary. 



Scheele's Green is another arsenical insecticide 

 recently placed on the market. According to a bulle- 

 tin of the United States Department of Agriculture, 

 it ''is similar to Paris green in color, and differs from 

 it only in lacking acetic acid ; in other words, it is a 

 simple arsenite of copper. It is a much finer powder 

 than Paris green, and therefore more easily kept in 

 suspension, and has the additional advantage of cost- 

 ing only about half as much per pound. When prop- 

 erly w^ashed and prepared by the manufacturers it is 



