ENTOMOLOGY 365 



tion to its use is the necessity of handling the poisons in its home 

 preparation. 



Arsenate of Lead. Arsenate of lead may be prepared at' home 

 by combining approximately 3 parts of crystallized arsenate of soda 

 with 7 parts of crystallized acetate of lead (sugar of lead) in water. 

 This gives a slight excess of acetate of lead. Each of the ingredients 

 should be dissolved separately in water in wooden vessels, and the 

 two solutions poured together into the spray tank filled with water. 

 The white, flocculent precipitate of arsenate of lead which imme- 

 diately results is extremely fine and remains in suspension much 

 longer than any other arsenical. Furthermore, prepared in this way 

 and diluted at once, there is secured a mixture that is chemically su- 

 perior to the combined product sold in paste form and that remains 

 in suspension better. Arsenate of soda costs wholesale about 10 cents 

 a pound, and first-class acetate of lead about 10 cents a pound. 



Arsenate of lead may be used at any strength from 3 to 15 

 pounds to 100 gallons of water without injury to the foliage, for the 

 reason that it contains little, if any, soluble arsenic. It is ordinarily 

 used at the rate of 4 to 6 pounds to the 100 gallons of water or Bor- 

 deaux mixture. In later years it has come into general use especially 

 for spraying plants sensitive to arsenical poisoning, such as peach, 

 and also in cases where it is necessary to make heavy applications. 

 Its safety as regards the burning of foliage and its adhesive quality 

 offset its greater cost, and it is now much used in the codling moth 

 work and general arsenical spraying. 



In the home preparation of this arsenical, the number of pounds 

 of the poison per 100 gallons of water as given in directions for use 

 should be understood to mean the combined weights of the two in- 

 gredients. In point of fact, the resulting lead arsenate is only about 

 half the actual weight of the two ingredients, which explains in 

 part the apparently excessive amounts used as compared with other 

 arsenicals. 



A good many brands of arsenate of lead can be purchased on 

 the market, usually in the form of heavy pastes. As already indi- 

 cated, they have not the same power of remaining in suspension as 

 the freshly made product, but are otherwise, if properly made, quite 

 satisfactory. The water content, which is variable, should be spe- 

 cifically indicated and guaranteed, to make it possible to use the 

 poison at the strength desired. Arsenite of lead is a compound very 

 similar to the arsenate of lead, but it contains a less percentage of ar- 

 senic. It is prepared from sodium arsenite. 



General Consideration. In point of solubility and correspond- 

 ing danger of scalding the foliage, these arsenicals fall in the follow- 

 ing order, the least soluble first: Arsenate of lead, arsenite of lime, 

 Paris green, copper arsenite, and London purple. In point of cost 

 the arsenite of lime is much cheaper than the other arsenicals, and 

 the arsenate of lead, at the rate at which it is necessary to use it, 

 much the most expensive. But after all the main cost is in the appli- 

 cation, and it is therefore well worth while to secure a good arsenical 

 and get the best results. 



