144 McDonnell and Smith— Xectd-CAfo 1 )' Arsenate. 



It was found, however, that a product of practically theoret- 

 ical composition was obtained by diluting a boiling saturated 

 solution of sodium or potassium chloride, to which had been 

 added arsenic acid and lead acetate, with a small amount of 

 boiling- water : To 2000 co saturated sodium chloride solution at 

 boiling temperature were added approximately 30 grams of 

 arsenic acid, then lead acetate solution until a permanent pre- 

 cipitate remained, filtered and added 600" of boiling water to 

 the clear filtrate. A precipitate formed almost immediately 

 and settled rapidly, leaving a clear solution. This was decanted 

 after a few minutes and the precipitate washed by decantation 

 with boiling water until no reaction for chlorine was obtained 

 in the wash water. The precipitate recovered weighed 4*8 

 grains and consisted of beautiful crystals similar in appearance 

 to those shown in fig. 2. In 'size they averaged about 

 •015 x •01 n " n , but some were observed as large as -10 x •05" 

 Analysis : 



Lead oxide, PbO. .1 73- 



Sodium oxide, Na a O -64 



Arsenic pentoxide, As,0 6 23-18 



Chlorine, CI 2-46 



100-18 

 O, equivalent to CI . . 0-.55 



k£mm * 



99-63 



arsenates are added to lead chloride. However when a solution of lead 

 chloride is added to sodium or potassium dihydrogen arsenate, the latter 

 remaining in excess, dilead arsenate is formed. A chlor arsenate will be 

 precipitated by lead acetate or nitrate from a solution of disodium arsenate 

 containing sodium chloride. 



*The same compound was formed, but in much smaller crystals, when the 

 boiling saturated sodium (or potassium) chloride solution, prepared as 

 described, was added quickly to three to six times its volume of boiling 

 water. However, when a portion of the same solution was added, at boiling 

 temperature, to five times its volume of cold water (28-30° C), a crystalline 

 precipitate was produced which analyzed : 



Lead oxide, PbO 73'80# 



Sodium oxide. Na Q -32 



Arsenic pentoxide, As a 5 22'30 



Chlorine, CI 3"42 



Water (expelled on ignition) -97 



100-81 

 O, equivalent to CI - 77 



100-04 

 This corresponds closely to the formula : 2Pb 3 (Ae04)2.PbCl2.H 2 0, or 

 Pb 5 (PbCl)a(AsO. ) )j.H.jO. This experiment was repeated a number of times 

 and always resulted in the production of this compound, which differs from 

 mimetite in containing a greater proportion of lead chloride and also a small 

 amount, apparently one molecule, of water of crystallization. 



