ONE HUNDRED YEAES OF CHEMISTEY 293 



more than twenty other atomic weights, but this great 

 amount of work did not bring about any considerable 

 improvement, for it appears that Dumas did not greatly 

 excel Berzelius in accuracy, and that the latter had made 

 one of his most noticeable errors in connection with 

 carbon. 



Soon after assisting Dumas in the work upon carbon, 

 Stas began his very extensive and accurate, independent 

 determinations, leading to the publication of a book in 

 1867 describing his work. Stas made many improve- 

 ments in methods by the use of great care in purifying 

 the substances employed, and especially by using large 

 quantities of material in his determinations, thus dimin- 

 ishing the proportional errors in weighing. His results, 

 which dealt with most of the common elements, were 

 accepted with much confidence by chemists everywhere. 



Stas reached the conclusion that there could be no real 

 foundation for Prout's hypothesis, since so many of his 

 atomic weights varied from whole numbers, and this 

 opinion has been generally accepted. 



The first accurate atomic weight determination pub- 

 lished in the Journal was that by Mallett on lithium (22, 

 349, 1856; 28, 349, 1859), showing a result almost identi- 

 cal with that accepted at the present time. Johnson and 

 Allen's determination (35, 94, 1863) on the rare element 

 caesium was carried out with extraordinary accuracy. 

 Lee, working with Wolcott Gibbs, made good determina- 

 tions on nickel and cobalt (2, 44, 1871). The work of 

 Cooke on antimony (15, 41, 107, 1878) was excellent. 



Concerning the more recent work published elsewhere 

 than in the Journal, attention should be called particu- 

 larly to the investigations that have been carried on for 

 the past twenty-five years by Richards and his associates 

 at Harvard University. Richards has shown masterly 

 ability in the selection of methods and in avoiding errors. 

 His results have displayed such marvelous agreements 

 among repeated determinations by the same and by dif- 

 ferent processes as to inspire the greatest confidence. 

 His work has been very extensive, and it is a great credit 

 to our country that this atomic weight work, so superior 

 to all that has been previously done, is being carried 

 out here. 



