ATOMIC WEIGHTS " 503 



to be approximate rather than exact. In each case the weighed oxide 

 was dissolved in an excess of half-normal sulphuric acid, the excess 

 being afterwards measured by titration with tenth-normal sodium hy- 

 droxide solution. From the data thus obtained, by a process which is 

 not clearly explained, the authors compute the proportion of oxygen in 

 the axides, and thence deduce the atomic weights of the several methods. 

 It would have been better to have given the HoSO^ equivalent to the 

 oxide, and then to have made a more direct calculation. However, I cite 

 the determinations for what they may be worth, their value being essen- 

 tially corroborative. For lanthanum the authors give the following 

 determinations : 



.5125 

 .5256 

 .4835 

 .5235 

 .4815 

 .5156 

 .5348 



Mean, 139.09, ± .0430 



We may now combine the similar means into general means, and de- 

 duce a value for the atomic weight of lantlianum. For the percentage of 

 oxide in sulphate we have estimates as follows. The single experiments 

 of Czudnowicz and of Erk are assigned the probable error and weight of 

 a single experiment in Hermann's series : 



Czudnowicz 58.668, ± .027 



Erk 57.068, ± .027 



Hermann 57.654, ±: .016 



Zschiesche 57.021, ± .051 



Marignac 57.549, ± .0112 



Cleve, earlier series 57.619, zt .0085 



Cleve, later series 57.480, ± .0040 



Brauner, 1882, first series 57.5575, ± .0057 



Brauner, 1882, second series 57.472, it .0086 



Bauer 57.541, ± .0136 



Bettendorff 57.524, ± .0006 



Bodman 57.508. ± .0070 



Jones, 1902 57.544, ± .0006 



Brauner and Pavlicek, first 57.564, ± .0047 



Brauner and Pavlicek, second 57.550, ±.0048 



Brauner and PavliCek, third 57.5843, ± .00075 



Jones, 1903, porcelain series 57.549, ± .0010 



Jones, 1903, platinum series 57.586, ± .0027 



Brill 57.695, ± .0207 



General mean 57.5469, ± .00034 



