Biography of Berzelius. 211 



firmly, and disputed the hypotheses of Thomson, Dalton, and 

 other chemists, who assumed that in two volumes of hydro- 

 gen there were as many atoms as in one volume of oxygen. 

 Subsequently, when by the direct determination of the spe- 

 cific weights of sulphur, phosphorus, and mercury vapours, 

 made by Dumas and Mitscherlich, this assumption of Ber- 

 zelius was not generally confirmed, he limited its application 

 to the permanent gases alone. 



He was on this account compelled frequently to assume 

 two atoms where other chemists assumed only one atom. 

 He therefore introduced double atoms in those cases where 

 they were the equivalent for one atom of another substance. 

 Many chemists, especially in Germany, have not followed 

 this view ; and Leop. Gmelin, in the last edition of his 

 " Handbucli" as well as Liebig and his followers, have com- 

 menced to take the atomic weights of hydrogen, nitrogen, 

 chlorine, bromine, iodine, fluorine, and phosphorus, as double 

 those adopted by Berzelius, and many French chemists also 

 entertain this view. The assumption that the so-called equi- 

 valents are identical in meaning with the term atoms, has 

 indeed so much probability, that the agreement of so many 

 chemists in this respect cannot be remarkable. 



Notwithstanding this, Berzelius continued to the last to 

 adhere to his old atomic weights, and the reasons which, in 

 the last edition of his Lehrbuch, he has assigned for doing 

 this, are so strong, that they cannot well be set aside. These 

 he derives especially from the isomorphism of perchlorates 

 and permanganates as proved by Mitscherlich, and from which 

 it follows that a double atom of chlorine can replace a double 

 atom of manganese. Since, however, manganese is in its com- 

 pounds isomorphous with iron and chromium, for instance, 

 in the alums, and since chromium in chromates has the same 

 form as sulphates, a simple atom of chlorine must be able to 

 replace an atom of sulphur. But if perchloric acid consists 

 of a double atom of chlorine, combined with seven atoms of 

 oxygen, then the hypochlorous acid contains only one atom 

 oxygen, combined with the same quantity of chlorine as in the 

 perchloric ; and as hypochlorous acid consists of two volumes 

 chlorine and one volume oxygen, the volumes of the two ele- 



