Some Peculiar Double Salts of Lead 17 



The appearance of this salt, as well as that of a similar 

 compound in the waste liquor from the potassium double salt, 

 as by-products, may be regarded as indicating the general na- 

 ture of the reaction, showing that a partial interchange takes 

 place between the lead iodid and the alkaline acetate, thus fur- 

 nishing additional evidence in favor of the theory which has 

 been proposed in explanation of the double salt formation. 



The Lead Salt. — In his paper dealing with the salts of the 



type P^<7- rr r^ Carius^ states that water decomposes 



these, throwing out a white powder, which, however, soon 

 goes completely into solution. He further says that the halogen 

 salts of lead are soluble in lead acetate, and that the compounds 

 obtained by the two methods are identical to this. Based upon a 

 chlorin estimation, he ascribes the formula 



Pb<^Cimo-,'^PKCiHzOi^i '6H2O. 



Although Carius mentions the fact that lead iodid acts like the 

 chlorid, he does not give any description of the iodin com- 

 pound. A repetition of his work reveals the probable cause 

 of this omission, for when lead iodid is dissolved in a water 

 solution of lead acetate, the basic iodid of lead is invariably 

 formed; the same is indeed the case when an alcoholic solu- 

 tion is used, unless a relatively large amount of acetic acid be 

 .idded. 



The iodid is not so readily soluble in lead acetate solution 

 as in solutions of the alkaline acetates. The following propor- 

 tions used in several instances will give an idea of the solubility : 

 50 gr. lead acetate were dissolved in 100 cc. 93 per cent alcohol 

 and 30 cc. glacial acetic acid; in this, at the boiling tempera- 

 ture, there were dissolved about 4 gr. lead iodid. The solution 

 does not have to be cooled in a vacuum, as no decomposition 

 takes place during the precipitation. The crystals obtained 

 were white, well defined, and consisted of simple monoclinic 

 forms. 



323 



