LECTURE X.] HISTORY OF CHEMISTRY. 175 



completeness and conscientiousness were his watchwords, and 

 these were adhered to. 



Since formulae, for Gmelin's school, merely represented the 

 composition of substances by means of a contracted style of 

 writing them, these chemists were at liberty to choose their 

 " equivalents " or "combining weights" at will from the pos- 

 sible multiples. The guiding principle appeared to them to be 

 simplicity in symbolising, and therefore their numbers possess 

 little real significance as regards development. I shall merely 

 remark that they adopted the formulae of Berzelius for most 

 compounds, and, in doing so, they regarded the double atom 

 as an equivalent. They arrived at this by halving the atomic 

 weights of oxygen, sulphur, carbon, selenium, etc., with refer- 

 ence to hydrogen, chlorine, bromine, iodine, nitrogen, phos- 

 phorus, and the metals.' 2 



It must not be supposed, however, that, at the beginning 

 of the forties, the atomic weights of Berzelius were no longer 

 used. On the contrary, they were still employed by Liebig and 

 his numerous and important followers, 3 and it was only towards 

 the end of the decade (after the appearance of Gerhardt's paper) 

 that the latter also made use of Gmelin's equivalents. I have 

 already indicated in a previous lecture what the reasons were 

 that brought about this revolt from the atomic theory. 4 Although 

 I said there that none of the physical rules which expressed 

 relations between the atomic weight and certain properties of 

 matter, appeared capable of general application, on the other 

 hand, the law which had induced Dalton to advance the atomic 

 theory, that is, the law of multiple proportions, was still un- 

 attacked. The examination of numerous organic compounds 

 whose investigation was already completed, had only tended to 

 confirm it. No doubt, it had become necessary to admit that 

 a much larger number of atoms can unite with one another 



2 Compare Gmelin, Handbuch. First Edition, 34. At this time Gmelin 

 also halves the atomic weight of phosphorus, and so writes phosphoric acid 

 P a O.- as Berzelius did. 3 The sign for the double atom is not employed 

 in Liebig's Annalen, and HLO is therefore printed instead of HO, as Liebig 

 observes from want of the necessary types. 4 Compare p. 1 06. 



