130 THE ATOMIC WEIGHTS. 



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

 ride. In one estimation 8.700 grammes PbCl 2 saturated 6.750 of Ag. 

 The chloride contained .009 of impurity ; hence, correcting, Ag : PbCI 2 : : 

 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 in- 

 dicated 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 excellent 

 results. Two series of experiments were made, with from 103 to 2pO 

 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, 100 of lead 

 yield of nitrate : 



A. 



159-973 

 159.975 



159.982 



159-975 

 159.968 



J59-973 

 Mean, 159.9743, =fc .0012 



159.970 

 159.964 

 159-959 

 I59-965 



Mean, 159.9645, .0015 

 Mean from both series, 159.9704, 2 .0010 



There is still another set of experiments upon lead nitrate, originally 

 intended to fix the atomic weight of nitrogen, which may properly be 

 included here. It was carried out by Anderson f in Svanberg's labora- 

 tory, and has also appeared under Svanberg's name. Lead nitrate was 

 carefully ignited, and the residual oxide weighed, with the following 

 results : 



5.19485 grm. PbN 2 O 6 gave 3.5017 grm. PbO. 67.4071 per cent. 



9.7244 6.5546 " 67.4037 " 



9.2181 6.2134 " 67.4044 " 



9.6530 6.5057 " 67.3957 



Mean, 67.4027, i .0016 



* Aronsteiii's translation, 316. 



t Ann. Chim. Phys. (3), 9, 254. 1843. 



