C^U) SCIENTIFIC KECUEJ) FOR 1885. 



On the Unit used in Calculatimj the Atomic Weights (by Lothar Meyer 

 aiul Karl Seubert). — Tlie controversy arising: immediately after the pro- 

 posal of Dalton's atomic theory, as to the unit upon which the numerical 

 values of the atomic weipcht should be based has for half a century 

 divided chemists into two schools. While Dalton and, later, Leopold 

 Gmelin, from theoretical and philosoj^hical considerations, chose the 

 smallest atomic weight, that of hydrogen, as the measure of all the rest, 

 Wollaston and Berzelius chose that of oxygen, ijartly because they did 

 not i^lace so high a value on theoretical views, and partly on the purely 

 practical ground that many elements can be compared directly with 

 oxygen, whereas they can be only indirectly compared with hydrogen. 

 When the Dalton unit, the hydrogen atom, gradually obtained the 

 upper hand, the old controversy appeared to have been laid aside, and 

 consequently it was to be hoped that the recent more exact investiga- 

 tions of the laws which govern the numerical values of the atomic 

 weights would be directed from the same point of view. This hope, 

 however, has unfortunately not been fulfilled, as the old Wollastou- 

 Berzeliu^ unit has lately again come into use in a difterent — and as we 

 believe — more dangerous form. 



As is well known, J. S. Stas has from his own observation as well as 

 those of others deduced as the most highly probable result that the 

 atomic weight of oxygen is not quite sixteen times as great as that of 

 hydrogen, but on the contrary is about ^^o of its value less than IG H. 

 That is when H=l, 0=15-96. Many chemists, however, content them- 

 selves with numerical values founded on the more simple ratio of 

 H: 0=1 ; ](>, regarding the difference of ^^j as of very little practical 

 consideration. And the hope that the old controversy over the choice 

 of the unit would disappear upon a recalculation of the atomic weights 

 has unfortunately not been fultilled. The desn-e to do away with the 

 unit 0=100 is universal; all chemists prefer referring atomic weights 

 to hydrogen, but they do not agree as to the way in which this is to be 

 done. Some refer all atomic weights to = 16, when H = l-002o, and 

 others to H=l. In consequence of these different views all the other 

 atomic weights Huctuate to the eateut of about ^ per cent, of their 

 value, a very undesirable state of affairs, leading to confusion and per- 

 l)lexity. The authors maintain that the real cause prompting the 

 adoption of 0=16 is a secret fondness for Front's hypothesis. 



The authors admit that the error introduced by making 0=16 is n)uch 

 smaller than the unavoidable errors of observation so far as inonjanic 

 compounds are concerned, but they show that in the analysis oH organic 

 compounds it is quite otherwise. From a table showing the percentages 

 of hydrogen and carbon in the paraffins containing 30 and 31 carbon 

 atoms and their derived alcohols and acids, it is evident that the vari- 

 ations in the calculated percentages of carbon dioxide reach the tenths 

 of a per cent., a difference often greater than that obtained from two 

 adjacent hydrocarbons in a homologous series. 



