OF ARTS AND SCIENCES. 5 



became an important subject for consideration; but it is evidently 

 of little use to recalculate such heterogeneous results. The neces- 

 sity for a careful experimental revision is very apparent. Such a 

 revision would be especially interesting in view of the fact that 

 barium is a member of one of the best marked series of elements 

 known, — a series which might yield important information regard- 

 ing a possible mathematical relation of the atomic weights. More- 

 over, the atomic weights of no less than eighteen other elements * 

 have been determined, at one time or another, by reference to baric 

 sulphate. Most of these determinations have been made without 

 the least precaution with regard to the baric chloride occluded in 

 the precipitated sulphate, or on account of the solubility of the sul- 

 phate itself; but even if the method had been satisfactory, the 

 determinations could not be considered as anything more than 

 crude approximations, because of our uncertainty regarding the 

 molecular weight of baric sulphate. 



These were some of the considerations which prompted the pres- 

 ent undertaking. It is not unnatural that the revision should 

 have been begun with the more or less strong belief that the atomic 

 weight of barium could not be far from 137.1; but the progress of 

 the work has completely overthrown this belief, and has indicated 

 a much higher value. 



Balance and Weights. 



The balance and weights were identical with those used in the 

 latter part of the investigation upon copper,! hence a further de- 

 scription of them is unnecessary. The weights were gently and 

 carefully rubbed, and again standardized with reference to each 

 other; a proceeding which yielded values essentially identical with 

 the two previous standardizations. The first ten-gramme weight 

 was also compared from time to time with the platinum weight 

 which had been carefully standardized in Washington,! in order 

 to test its constancy. 



True Grammes. 



Oct. 18, 1891 Ten-gramme weight = 10.00023 



May 16, 1892 '' '' =10.00023 



Nov. 1, 1892 <' ^' = 10.00022 



Nov. 2, 1892 '' '' = 10.00020 



* Li, Be, F, Mg, Si, V, Cr, Ni, Cu, Se, Y, In, (Ba), La, Ce, Di, Au, Tl, Th. 

 Compare L. Meyer and Seubert's " Atomgewichte," p. 165. 

 t These Proceedings, XXVI. 242. 



