Some Peculiar Double Salts of Lead 



Biderable extent upon the conditions of handling. The double 

 Bait is apparently more soluble than its constituents, and under 

 practically similar conditions one would sometimes get lead 

 iodid crystallizing out first ; at other times sodium acetate. 

 The approximate quantities which led to the best results were : 

 40 to 50 gr. sodium acetate in enough alcohol (about 80 per 

 cent) to make a fairly concentrated solution, 2 to 3 cc. glacial 

 acetic acid and 10 to 12 gr. lead iodid. From this solution, 

 on cooling in a partial vacuum, no lead iodid separated out, 

 but several crops of sodium acetate were obtained. These 

 were removed as fast as formed, and if decomposition set in 

 during the handling, by heating the solution it could be again 

 obtained clear. This was kept up until no further separation 

 of sodium acetate took place, but upon slow evaporation in 

 a partial vacuum, large, almost wdiite, crystals were obtained. 

 It is easy to judge of the relative purity of the several crops of 

 sodium acetate by taking a portion of the salt, pressing out 

 rapidly between drying paper, then moistening with water or 

 with acetic acid. Instant decomposition takes place, and as 

 lead iodid is one of the products of decomposition of the double 

 salt, the depth of color due to this serves as a very good quali- 

 tative test. 



Several prepara'tions of the salt were made, and the crystal- 

 lized product was carefully examined each time to de- 

 termine if there was a tendency to the formation of a uni- 

 form substance. This was found to be true except in one 

 instance, to be noted later. The crystals consist of large, flat 

 orthorhombic plates, usually admixed with a small amount of 

 thin, pearly scales, from which they could be easily separated 

 mechanically. 



The crystal form and planes usually oc- 

 curring are shown in the accompanying 

 figure. Crystals up to 3 mm. in length by 

 I to 2 mm. in width were obtained. The 

 planes were well defined, but no measure- 

 ments could be made, the necessary ap- 

 paratus not being at hand. 



a=P?i 



Figr. 1 



313 



