384 ECONOMIC ENTOMOLOGY 



water. The finer the particles the longer they remain in suspension, 

 consequently it should first of ^11 be made into a thin paste in a small 

 amount of water, and after it is in the barrel it should be kept in 

 suspension by a mixer. It cannot be used with lime-sulphur solution. 



The usual formula employed is: Paris green, i lb.; best stone lime, 

 I to 4 lb.; water, 160 gal. imperial or 200 gal. U. S. measure. The 

 Paris green is made into a paste with water and stirred into the lime- 

 and-water mixture. When used as a dry application for the potato 

 beetle, i lb. of Paris green is thoroughly mixed with 20 lb. cheap 

 flour, air-slaked lime or finely sifted land plaster. 



(b) Arsenite of Lime. — White arsenic (AS2O3), combined with 

 washing soda or sal soda (Na2C03) and quick lime (CaO), is frequently 

 used on account of its cheapness. The combination is made as follows: 



Dissolve I lb. white arsenic and i lb. sal soda in i gal. of water 

 by boiling in an iron vessel for 20 minutes. Add this while hot to 

 slake the lime; then add 2 gal. of water. Use 2 qt. of this to 40 gal. 

 of water. AS2O3 + NasCOg + Ca(0H)2 = Ca(As02)2 + CO2 + 

 2NaOH; or rather AS2O3 + NasCOg = 2NaAs02 + CO2; 2NaAs02 + 

 Ca(0H)2 = Ca(As02)2 + 2NaOH. 



(c) Arsenate of Lead. — This insecticide is preferred by many fruit 

 growers to Paris green since it adheres better to foliage, is less likely 

 to do injury, and no lime is required in standard preparations. 



The commercial form consists of a mixture of the neutral triplumbic 

 arsenate [Pb3(As04)2] and the acid plumbic hydrogen arsenate (PbH- 

 ASO4). The neutral product may be prepared by dissolving acetate 

 of lead (11 oz.) and arsenate of soda (4 oz.) in 120 gal. water. The 

 reaction is as follows: 



3Pb(C2H302)2 + 2Na3As04 = Pb3(AsOi)2 + 6NaC2H302. 



When lead nitrate is used instead of lead acetate more of the acid 

 arsenate is formed. 



For fruit trees 2 lb. of arsenate of lead (paste) to the barrel (40 

 gal.) of water is the usual strength. For the Potato Beetle 4 lb. 

 (paste) or 2 lb. (powder) to the barrel should be used. Acid brands 

 are apt to burn the leaves. 



Commercial arsenate of lead is put up in the paste, the usual form, 

 and the powder form of which but half the amount is required. The 

 former contains about 15 per cent. AS2O6; the latter has about Z2> P^r 



