CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A TABLE OF ATOMIC WEIGHTS. 

 By Theodore William Richards. 



Presented March 9, 1898. 



Since do natural constants are more used by chemists than the 

 atomic weights, it is a matter of great importance for every one, from 

 the chemical philosopher to the practical analyst, to have a convenient 

 table of them always at hand. Unfortunately the present state of our 

 science makes the selection of the values often a matter of personal 

 opinion ; and because this is the case, it is well that many of those who 

 have had experience in accurate quantitative analysis should express 

 their views. Hence arose the present work, which was begun solely 

 for use in Harvard College. 



It is true that an accurate table of atomic weights may sometimes 

 be less appropriate for the calculation of analyses than an inaccurate 

 one. For the constant errors of any one process are eliminated as 

 much as possible from the accurate table, and, moreover, all the results 

 are reduced to the vacuum standard. Of course neither of these refine- 

 ments is to be expected in common work, although many uncorrected 

 methods may yield results which are very consistent among themselves. 

 Obviously the best table for the practical calculation of analyses would 

 be a list of factors, in which each quantity had been found empirically 

 according to precisely the method which is to be employed in the anal- 

 ysis of an unknown substance.* Since, however, the errors of ordinary 

 work often eliminate one another, and since such a table of empirical 

 factors would have to be accompanied by exceedingly minute directions, 

 the scientifically accurate table of atomic weights is generally the most 

 convenient substitute for the factors demanded by the analyst, as well 

 as the most suitable basis for theoretical considerations concerning the 

 periodic system of the elements. 



* Compare Seubert, Berichte d. d. cliem. Gesell., XXI. 2180. 



