198 SPRAYING MATERIALS 



ever, sometimes injurious to trees, and one should take every 

 precaution possible to avoid trouble. 



There are two forms on the market, one of which, known as 

 the tri-plumbic form, has a higher percentage of lead and no 

 hydrogen; while the other, known as the standard, has a higher 

 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. 



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 it 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 dis- 

 solve, if not there will be some sediment. The value of this 

 test rests on the fact that the materials generally used to adulter- 

 ate 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 when 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. 



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

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



