ARSENATE OF LEAD 197 



In the first of these classes, at the present time, the arsenate 

 of lead is used much more generally than any other form, with 

 Paris green as a second. Several others are on the market and 

 are used to a limited extent, but from the commercial orchard 

 standpoint they may be ignored. 



Arsenate of Lead. — The great advantages of arsenate of lead 

 are (1) that it is very adhesive, remaining on the leaves through 

 the entire season; (2) that it is finely divided, remaining in sus- 

 pension much longer than Paris green; and (3) that it is usually 

 harmless to foliage. This is a strong combination and it is small 

 wonder that arsenate of lead is so generally used. It is, how- 

 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. 

 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 water. 



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 dissolve, if not 

 pure there will be some sediment. Tlie 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 



