ATOMIC WEIGHTS 531 



In his first series Braimer found, for the same percentage, 57.871 

 and 57.868. Including these, the eight determination?, taken as one 

 series, give a mean of 57. 871, ±.0021. 



Hence Pr= 140.97. 



Combining this mean with other means for the same ratio we have — 



Jones 57.796. ± .0016 



Scheele, first 57.805, ± .0139 



second 57.737, ± .0117 



third 57.807, ± .0026 



Brauner 57.871, ± .0021 



General mean 57.8194, ± .0010 



Three other determinations by Welsbach ' were jiublished in 1903. 

 He used the sulphate method and found Pr = 140.64, 140.50 and 140.56 

 when = 16. Unfortunately, he gave no weighings, nor did he state 

 what value he used for the atomic weight of sulphur. His figures, there- 

 fore, are unavailable for discussion now. 



There are also three determinations by Feit and Przibylla,' who used 

 the peculiar volumetric method already described under lanthanum. 

 Their results are as follows : 



.0189 



The ratios for praseodymium now are — 



(1). Pr,(SOj3.8H„0:PrA: : 100: 46.211. ± .0050 

 (2). Pr,(S0j3:PrA: :100:57.8194, ± .0010 

 (3). 30,03 :Pr,( 304)3: :100:262.680, ± .1113 

 (4). 30,03 tPrsOj: : 100: 152.720, ± .0148 

 (5). 0:Pr:: 16: 140.545, ±.0189 



1 Sitzungsb. Wien. Akad., 112, 1037. 1903. 

 ^Zeitsch. anorg. Chem., 50, 258. 1906. 



