58 THE GYPSY MOTH- -APPENDIX. 



of lead and arsenate of soda. Owing to the variable com- 

 position of these commercial salts, a chemical analysis of 

 each is indispensable, as indicating the relative amounts to 

 be used. All such calculations must be based upon the 

 quantity of lead oxide (PbO) found in the lead salt and that 

 of arsenic pentoxide (As 2 O s ) contained in the arsenate of 

 soda, making due allowance for other acidulous radicals 

 which may precipitate the lead. 



Both the acetate and the nitrate of lead are extensively 

 used in paint and dyeing industries, and especially as mor- 

 dants in calico printing. Arsenate of soda is chiefly used 

 to remove mordants. 



Acetate of Lead, Lead Acetate, Sugar of Lead. 



Pb(C 2 H 3 O,),3H,0. 



So far as is known to the writer, this salt is the one gen- 

 erally used as a source of soluble lead oxide for the prepara- 

 tion of arsenate of lead. Acetate of lead may be obtained 

 in the market in all grades, from clear, transparent crystals 

 to dark gray or brown lumps, and is usually quite free from 

 adulteration. It is prepared either by exposing litharge 

 (PbO) to the action of the vapors of pyroligneous acid, 

 or by dissolving metallic lead in pyroligneous acid and re- 

 crystallizing the products from water solutions. Pure lead 

 acetate crystallizes in four-sided prisms, containing three 

 molecules of water of crystallization. Crystals formed by 

 the sudden cooling of a hot saturated water solution sepa- 

 rate in a more finely divided condition than those formed by 

 a slow evaporation. The finer crystals are especially desir- 

 able when the salt is to be used for technical purposes, or 

 when it is necessary to dissolve a large quantity in a short 

 space of time. 



When the crystallized salt is exposed to the action of the 

 air there is a rapid loss of water of crystallization (efflores- 

 cence) and also a slow formation of lead carbonate, due to the 

 action of carbon di-oxide contained in the air. Thus the 

 percentage composition of crystallized lead acetate may be 

 materially changed. Loss of weight by efflorescence yields 

 a product containing a higher percentage of actual lead 

 acetate than the original crystallized salt, accompanied by 



