RICHARDS. — A TABLE OP ATOMIC WEIGHTS. 631 



NOTE. 



The accompanying table of atomic weights is but little changed since last year. 

 Caesium is made 132.88 instead of 132.9; calcium, 40.13 instead of 40.1 ; iron, 55.88 

 instead of 55.9; hydrogen, 1.0076 instead of 1.0075; and nickel, 58.71 instead of 

 56.70. Tlie value for caesium is due to some work, as yet unpublished, of Richards 

 and Archibald, and that for calcium is increased in accuracy because the recent 

 investigation of Hinrichsen* supports the less recent Harvard value.t The other 

 very small changes are due simply to slight differences in the interpretation of 

 data already well known. The decimal might have been omitted from palladium, 

 because this element may still be a whole unit in doubt; but it has been retained 

 as a compromise. 



The differences between the present table, that of the German Committee,! and 

 that of F. W. Clarke,§ are diminishing year by year. Nevertheless to as many as 

 twenty-eight elements out of the seventy-seven are given values in these three 

 tables differing among themselves by over one tenth of a per cent ; namely, the 

 atomic weights of antimony, bismuth, cerium, columbium, fluorine, gadolinium, 

 germanium, helium, hydrogen, lanthanum, magnesium, mercury, neon, osmium, 

 palladium, platinum, potassium, samarium, scandium, selenium, tantalum, tellurium, 

 thorium, thulium, tin, titanium, uranium, and zirconium. To this list of uncertain 

 elements should be added erbium, gallium, glucinum, indium, terbium, tungsten, 

 ytterbium, upon which the three tables agree only because of lack of data upon 

 which to base a disagreement. Thus nearly half of the elements are still in doubt 

 by at least one part in a thousand. This circumstance is not so much a reproof to 

 the many earnest workers upon the subject, as an evidence of the great difficulty 

 of some of the problems involved. 



Three of the elements given in the list above should not properly be included 

 among the uncertain values, namely, hydrogen, magnesium, and potassium. The 

 first finds its way into the list because of the disregard of significant figures by the 

 German Committee, and the second chiefly because Clarke has included in his 

 calculation work upon magnesic oxide undoubtedly erroneous on account of tiie 

 presence of included gases. || The case of potassium is somewhat peculiar; for 

 in spite of the great wealth of data concerning tliis element, Clarke assigns to it 

 the value 39.11, while the German Committee chooses 39.15. The low value is 

 chiefly due to very unsatisfactory data concerning potassic iodide. To me it seems 

 that the most recent work of Stas is far more satisfactory than his earlier work or 

 than the work of any one else, hence the value 39.14 has been assigned to potassium 

 in the present table since its first publication. Careful analyses by E. H. Archi- 

 bald and myself confirm this conclusion. 



* Hinrichsen, Zeitschr. phys. Chem., 39, 311 (1901). 



t Richards, Journ. Am. Chem. Soc, 22, 72 (1900), also 24, 374 (1902). 



I Landolt, Ostwald, and Seubert, Extra insertion in Berichte d. d. ch. Ges. 1902, 

 Heft 1. 



§ F. W. Clarke, Journ. Am. Chem. Soc, 24, 201 (1902). 



II Richards and Rogers, These Proceedings, 28, 209 (1893). 



