INSECTICIDES AND FUNGICIDES. 5 



A few A\Titers claim that pyroarsenate, PbaAsoOr, may occur in com- 

 mercial products, but the e\'idence at hand does not support the assertion. 



Compositio7i. — The composition of theoretical acid, neutral and basic 

 lead arsenates is as follows : — 



From the above table it is evident that the acid lead arsenate as it is 

 sold in New England is considerably more concentrated than is either 

 the neutral lead arsenate or the basic lead arsenate. From economic 

 standpoints alone this matter is of importance. 



Physical Proj^erties. — These products, whether acid or mixed acid 

 and neutral arsenates, are usually smooth white pastes of finely divided, 

 amorphous particles, less than 1 f^ in size, ^\•ith a good power of suspension 

 and exceptional adhesiveness. The so-called neutral salt has almost in- 

 variably been a mixture of acid and neutral, and very little has been 

 marketed. The physical structure of the neutral salt, or of ini.xtures con- 

 taining considerable neutral lead arsenate, is rather inferior to that of the 

 acid salt, and the basic material used in southern California is said to be 

 relatively coarse and granular. The power of suspension is injured by 

 drying or freezing. These pastes are compact and "greasy," but fairly 

 miscible with water when properly handled. The acid salt is less com- 

 pact, has a lower specific gravity and higher power of suspension, and is 

 a more active poison than the neutral or basic. The specific gravity of 

 the acid salt (amorphous form) (10) at 15/15° C. is 5.93, the neutral (10), 

 7.32, and the basic (11), at 20/4° C, 7.105. 



More recently the dry powders have displaced the pastes in large 

 measure at a material sa\ang in cost of containers, transportation, possible 

 leakage and danger of injury on storage. This product is a white, bulk}^ 

 (fluffy) powder of fine amorphous particles, with a very high power of 

 suspension and excellent adhesiveness. The "old type" dry acid arsenate 

 ran about 40 cubic inches to the pound, and the "new type" 70 to SO 

 cubic inches. The neutral and basic products are more dense, but actual 

 figures are not available, as they are seldom if ever marketed in dry form. 

 The product, as offered in Massachusetts markets, is essentially the acid 

 arsenate. It is more readily miscible with water than the paste, and a time 

 saver in this respect. 



