March 31, 1899.] 



SCIENCE. 



4:11 



THE ATOMIC WEIGHTS— A QUARTER CEN- 

 TURY'S PROGRESS. 



It may be of interest ,so near the close of 

 the centurj^ to follow a good commercial 

 precedent and make an inventory and strike 

 a. balance so as to gain some idea of the 

 progress in chemistry. One portion of oi\r 

 stock in trade has caused us a gi-eat deal of 

 ti'onble all through this century. It was in- 



by Meudeleefi in the constiuction of his 

 first table and that given by Fownes, whose 

 text-book was very largely used in England 

 and in this country. For the later com- 

 parison we will make use of the tables given 

 by the American and German committees. 

 Sixtj'-three elements come under the com- 

 parison in the former case and seventy in 

 the latter. The comparative table follows: 



COJIPAEISON OF LISTS OF ATOMIC WEIGHTS. 



No. atomic weisjlits 



troduced as a ' new line ' at the beginning of 

 the century and has been of the greate.st 

 value, but has suiiered from serious fluctua- 

 tions. The so-called chemical constants, 

 namely, the atomic weights, which should 

 be constants but have not been, have for the 

 larger part of the century been in a humil- 

 iating condition of incertitude. But they 

 are improving, settling down to their true 

 values, as it were, and there is cause to take 

 heart of hope concerning them. 



Some thirty years ago the Periodic System 

 was announced. The atomic weights had 

 emerged from the slough into which they 

 had sunk by the middle of the centuiy, 

 thanks to the labors of Cannizzaro, Wil- 

 liamson and others, but still there was veiy 

 little unanimity except with regard to those 

 for wliich the fewest data were in our pos- 

 session. It is difhcult to select for com- 

 parison any representative tables of atomic 

 weights for these earlier years, as none were 

 authoritative. In those daj'S there were 

 no national nor international committees 

 to consider these matters. We shall not go 

 far wrong, however, if we take the list used 



While much is left to be desired, the im- 

 provement is most gratifying. In the 

 earlier tables 5.5.-5 per cent agreed within 

 0.1 of the value. The majority of these as 

 given in the table were whole numbers and 

 were simjjly rounded o&' because the frac- 

 tions were unknown. The tables of 1899 

 give 65.7 per cent, of all the elements as 

 agreeing to the same extent, and here the 

 most scrupulous care has been observed in 

 recording the fractional portions. S"early 

 eighty jjer cent, of the atomic weights used 

 at present vary by 0. 2 or less where in the 

 earlier tables this proportion was only 

 sixty -two per cent. Nearlj^ thirty per cent, 

 of the earlier atomic weights varied by 0.5 

 or more where onlj' five per cent vaiy now. 

 None of the i^resent atomic weights vaiy by 

 more than one whole number where four- 

 teen varied a quarter of a century ago, five 

 of these varying by more than five integers. 

 It is evident that the list is narrowing down 

 and that this blot of ignorance and inac- 

 curacy which has rested upon the science 

 will soon be removed. Few realize how 

 great the armj^ of Avorkers along this line 



