SELECTING AND PREPARING MATERIALS 



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action than the acid form. However, if used according to 

 directions, the acid lead arsenate is not likely to cause burn- 

 ing in most parts of the country. In California it has caused 

 severe burning, when used with hard or alkaline water. 



Lead arsenate may be purchased in either powder or paste 

 form, the paste form differing from the powder only in con- 

 taining about 48 percent of water. Most paste arsenates are 

 of the acid type. 



Objections to the paste form of lead arsenate are its bulk 

 and consequent increased freight and handling costs ; the tend- 

 ency of the water to separate out, making it difficult to mix 

 before using and affecting the accuracy of the measurements; 

 the tendency of the water to dry out of the mixture, leaving 

 it more concentrated than the analysis indicates; and the possi- 

 bility of leakage and bursting of the package, as a result of 

 freezing. Consequently the powder form is more commonly 

 used. It is colored a pale pink by most manufacturers so 

 that it cannot be mistaken for some non-poisonous compound. 



Arsenic in any form is an active and virulent poison when 

 taken internally. It should be stored and handled with this 

 in mind. So far as external effects are concerned, it may be 

 handled freely by the operator. 



a: 2. Calcium Arsenate, Among other stomach poisons for 

 chewing insects, arsenic in combination with calcium as cal- 

 cium arsenate is on the market. It is cheaper pound for 

 pound than lead arsenate and carries a higher arsenic content. 

 It is available in both paste and powder forms. As con- 

 stituted at present, it is not safe to use on stone fruits since 

 it causes severe burning. It also burns apple and pear foliage 

 in some sections. 



In planning a spray program which offers the maximum 

 of protection against insect pests without leaving excessive 

 spray residue, calcium arsenate is recommended in some sec- 

 tions as a substitute for lead arsenate in some of the cover 

 sprays. Add 3 pounds of hydrated lime to every pound of 

 calcium arsenate to decrease or prevent burning of the foliage. 



