I. 



Some Peculiar Double Salts of Lead 21 



appears, however, as if a condition of equilibrium were reached, 

 for it was found after several extractions, varying in length, 

 using the same salt, that all yielded practically the same 

 amount of iodin. The other products of the decomposition, 

 the acetates of lead and of the alkali metal, could be readily de- 

 tected qualitatively in the filtrate. 



A study of the decomposition reactions just noted suggests 

 that the first action of the reagent is to split up the salt into 

 the two components, e. g. : 



and that subsequently the iodid-acetate decomposes into lead 

 iodid and lead acetate, e. g., 



2. 2^^<G^3C>2""^'^^2+^'^<^ €21/302)2. 



It is, however, not at first sight easy to explain the forma- 

 tion of the basic iodid, for experiment shows that lead iodid is 

 not acted upon to any marked extent by either hot or cold 

 water with formation of a basic salt. P^urther, should it be 

 conceded that the iodid is converted directly by water into 

 basic iodid, Pbh-\-H20=PbI{^0H)-^HI, the presence of the 

 hydriodic acid — or of its salts, since in this case it would natur- 

 ally react with the alkaline acetate formed in reaction i, yield- 

 ing an alkaline iodid — could be readily detected. Examination 

 of the filtrates reveals traces only of iodid, such as might be 

 expected from the lead iodid in solution. If, on the other hand, 

 it be conceived that a part at least of the iodid-acetate is acted 

 upon by water and thus transformed into the basic iodide, 



then the addition of a relatively small quantity of acetic acid 

 should serve to prevent this last reaction from taking place. 

 It was found, however, that, in alcoholic solution, if added in 

 small quantities at a time, a relatively large amount of glacial 

 acetic acid could be used without affecting the result to any ap- 

 preciable extent; naturally, when added in very large quantity, 



327 



