ATOMIC WEIGHTS 



111 



A similar series of experiments with lead arsenate gave the subjoined 

 figures : 



PbsiAsO,),. PbCh. Per cent. PbCL. 



.38152 .35381 92.737 



.436197 .40449 92.731 



.57218 .530G5 92.742 



.60085 .55717 92.730 



.74123 .68736 92.732 



.77107 .71494 92.721 



.88282 .81858 92.723 



.97779 .90674 92.734 



Mean, 92.731, ± .0019 

 Hence As =75.0.5. 



Lead arsenate was also transformed into lead bromide, by heating in a 

 stream of h^-drobromic acid : 



PbBr,. Per cent. PbBr,. 



.73092 122.424 



.75567 122.451 



.80569 122.447 



Pb.iAsO,),. 

 .59704 

 .61712 

 .65799 



.0076 



Mean, 122.441, 

 Hence As = 74.916. 



All of Ebaugh's weights are reduced to a vacnum. 

 Silver arsenate was also chosen by Baxter and Coffin ^ for their de- 

 terminations of the atomic weight of arsenic. In some experiments 

 Ebaugh's method of heating in gaseous hydrochloric acid was adopted: 

 in others the arsenate was dissolved in nitric acid, and the silver then 

 precipitated as chloride or bromide. Corrections were applied, not only 

 for weighing in air, but also for traces of moisture in the initial sub- 

 stance. Different samples of the arsenate were prepared, which gave 

 slightly varying results for the atomic weight, and the determinations, 

 for that reason, fall into two groups. In series 1 and 2, which may be 

 treated as one here, the first five determinations were made by Ebaugh's 

 method, and the last two by solution and precipitation. The figures 

 thus obtained are as follows : 

 Ag^AsO,. 

 3.17276 

 2.65042 

 3.51128 

 5.83614 

 5.722.52 

 4.50149 

 3.38270 



Hence As =74.956. 



Mean, 92.9550, ± .00036 



Jovirn. Anier. cnieni. Soc, 31, 297. 1009. 



