198 SPRAYING MATERIALS 



percentage of arsenic but also has some hydrogen in it. This 

 latter form, while more effective pound for pound in killing 

 insects, is also more dangerous to plants. On such tender foliage 

 as Japanese plums and the peach it is sometimes injurious. 

 Arsenate of lead can be had either as a paste carrying about 50 

 per cent of water, or as a dry powder. The dry form is rapidly 

 replacing the paste as the cost of transportation and handling is 

 less, and it is much less work to get it mixed with w^ater. 



Paris Green. — The only advantage of Paris green is that in 

 some sections it is more easily secured than arsenate of lead; 

 and possibly we might add a second, that is has a very distinctive 

 color which prevents its ever being mistaken for anything else. 

 There is now little danger that it will be adulterated, but if 

 anyone wishes to test it he may easily do so. Put a small quantity 

 of Paris green in a glass tube or bottle and pour on it some strong 

 ammonia. If the Paris green is pure it will all dissolve, if not 

 pure there will be some sediment. The value of this test rests on 

 the fact that the materials generally used to adulterate Paris 

 green are not soluble in ammonia, while pure Paris green is 

 soluble in ammonia. When some cheap material which is soluble 

 is discovered the test will lose its value. However, with our 

 present laws and methods of enforcing them, there is relatively 

 little danger from adulterated materials. 



It is usually recommended to use Paris green at the rate of 

 four ounces to 50 gallons of water, but many orchardists use 

 it at the rate of five or six ounces to 50 gallons on the theory that 

 poison is cheaper than labor, and at the latter strength they are 

 sure of killing the insect enemies. It is well to add an equal 

 weight of lime w^hen the Paris green is not used in combination 

 with a fungicide. The lime combines with any soluble arsenic 

 which may be present. 



Contact Insect Sprays. — There are four contact insecticides 

 which are very commonly used, each one of which has its good 

 points. 



Miscihle Oils.— First of all there are the soluble, or, more 

 properly, the miscible, oils. There are several of them, but they 

 all agree in being made from crude petroleum and in mixing 



