202 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



Mean, 96.890, ± .0704 



Hence Pb = 206.84. 



For the ratio between lead chloride and silver we have a series of re- 

 sults by Marignac and one experiment by Dumas. There are also un- 

 available data by Turner and by Berzelius. 



Marignac/ applying the method used in his researches upon barium 

 and strontium, and working with lead chloride which had been dried at 

 300°, obtained these results. The third column gives the ratio between 

 PbCL and 100 parts of Ag: 



Mean, 128.721, ± .016 



Hence Pb = 206.79. 



Dumas," in his investigations, found that lead chloride retains traces 

 of water even at 250°, and is sometimes also contaminated with oxychlo- 

 ride. In one estimation 8.700 grammes PbCU saturated 6.750 of Ag. 

 The chloride contained .009 of impurity; hence, correcting, Ag: PbCL:: 

 100 : 128.750. If we assign this figure equal weight with those of Marig- 

 nac, we get as the mean of all 128.7266, ±.013. The sources of error 

 indicated by Dumas, if they are really involved in this mean, would tend 

 slightly to raise the atomic weight of lead. 



The synthesis of lead nitrate, as carried out by Stas,* gives better 

 results. Two series of experiments were made, with from 103 to 250 

 grammes of lead in each determination. The metal was dissolved in 

 nitric acid, the solution evaporated to dryness with extreme care, and 

 the nitrate weighed. All weighings were reduced to the vacuum standard. 

 In series A the lead nitrate was dried in an air current at a temperature 

 of about 155°. In series B the drying was effected in vacuo. The data 

 are as follows, together with the ratio of nitrate to 100 parts of lead : 



1 Journ. prakt. Chem., 74, 218. 1858. Oeuvres Completes, 1, 574. 



2 Ann. Chem. Pharm., 113, 35. 1860. 

 ' Oeuvres Completes, 1, 386. 



