REPORT OF THE CHEMIST 



183 



SESSIONAL PAPER No. 16 



drawn up. With certain brands of the ' dry ' arsenate of soda less acetate of lead 

 would suffice than is indicated, but, that there may be no risk of injury to foliaga, 

 the formulae provide for an excess of lead even when the driest, or most modified, 

 brand of arsenate of soda is used. 



Formulae for Arsenate of Lead Sprays. 



A. This spray is, approximately, equivalent in arsenical strength to 2 lbs. arsenate 

 of lead paste (50 per cent arsenate of lead) per 40 gallons. 



B. This spray is, approximately, equivalent in arsenical strength to 3 lbs. arsenate 

 of lead paste (50 per cent arsenate of lead) per 40 gallons. 



In preparing the spray, the arsenate of soda and acetate of lead are dissolved in 

 separate vessels, using in each case from 1 to 2 gallons of water — the exact quantity 

 is of no moment. When dissolved, pour the two solutions simultaneously into a 

 40-gallon barrel two-thirds full of water, and finally fill to the containing mark. 

 This method will ensure the precipitation of the arsenate of lead in a very finely 

 divided form which will remain in suspension much longer than if the precipitation 

 is made from more concentrated solutions and subsequently diluted. 



ARSENITE OP LIME. 



So far as Canadian exi>erience is concerned this is practically a new insecticide, 

 though its properties as an insoluble compound, harmless to foliage and an effective 

 poison for biting insects, have long been known. Thus, Lodeman, in his manual 

 ' The Spraying of Plants,' 1896, wrote ' As an insecticide it is probably not surpassed 

 by any compound of arsenic; it is advisable to mix some colouring matter with the 

 poison to lessen the danger of mistaking it for some other article.' 



Arsenite of lime is not upon the market, but its preparation is not a matter of 

 great difficulty. The method more commonly advocated involves, as the first step, the 

 formation of arsenite of soda by the boiling together of white arsenic and washing 

 soda (sal soda or carbonate of soda, in crystals). The proportions generally recom- 

 mended are white arsenic 1 lb., washing soda 4 lbs., water, 1 gallon. These compounds 

 dissolve very readily as the liquid approaches the boiling point, and further heating is 

 unnecessary when they have passed into solution. The result is a solution of arsenite 

 of soda. This cannot he used as a spray as it is strongly corrosive and would quickly 

 strip the trees of their foliage. It must he converted into arsenite of lime. ' 



The conversion of the arsenite of soda into arsesnite of lime constitutes the 

 second and very essential part of the process; it may be accomplished in one of two 

 ways as follows: 



1. Thoroughly slake two pounds of good, fresh quick lime and stir into 40 

 gallons of water; then pour in with constant stirring of the lime water one pint of 

 the arsenite of soda solution. The spray is ready for use immediately as the forma- 

 tion of arsenite of lime takes place at once. This spray contains 2 ounces of white 

 arsenic or as much arsenic as one made by adding 4 ounces of Paris green to 40 

 gallons. The above proportions allow for a fair excess of lime, which serves the 

 double purpose of preventing injury to the foliage and of making visible the degree 

 of thoroughness with which the. spray has been applied. 



