MATERIALS 23 



The arsenate of soda and the acetate of lead are 

 each dissolved separately in 5 gallons of the waten 

 and the solutions mixed together. The dissolving 

 may be effected most conveniently in this, and in 

 all other similar cases, by tying the solid in a piece of 

 sacking, and hanging it in the water, so as to be only 

 just immersed below the surface. 



The above proportions will ensure there always being 

 an excess of lead present, and, as different samples 

 of sodium arsenate are liable to contain less arsenic 

 than those on which these proportions are based 

 the excess of lead may be considerable. It is more 

 economical, therefore, to add the lead acetate gradually 

 to the arsenate, examining the liquid between suc- 

 cessive additions, by allowing it to settle, and adding 

 no more of the lead as soon as further additions fail 

 to produce any further cloudiness. 



The strength of the wash mentioned above is the 

 greatest which should be used, and weaker prepara- 

 tions are generally effective : the actual quantities in the 

 10 gallons may be reduced to one-half or one-quarter 

 of those given, but both materials must be reduced in 

 the same proportions, the weight of lead acetate being 

 always double that of the crystallised sodium arsenate, 

 or 3^ times that of the crude sodium arsenate. Fur- 

 ther details as to the arsenates of lead will be found 

 in the Sixth Report of the Woburn Experimental 

 Fruit Farm. 



A ready-made arsenate of lead of American origin 

 is now on the market, in the form of a paste (Swift's 

 arsenate), containing half its weight of dry arsenate, 

 and growers would find it more satisfactory to use 



