CHEMISTRY OF THE NINETEENTH CENTURY. 615 



Berzelius has stamped the nomenclature of chemistry with the 

 impress of another idea, namely, the electro-chemical theory. The 

 decomposition of water and other compounds by the galvanic battery 

 need not be described in this place. Suffice it to say, as an example, 

 that when a hydrochloric acid is made to form part of the galvanic cir- 

 cuit, it is decomposed, chlorine being liberated from the positive pole, 

 and hydrogen from the negative pole. Similarly with other binary com- 

 pounds, one constituent appears at one pole, the other at the other 

 pole. If sulphate of soda is the subject of experiment, sulphuric acid 

 separates round the positive pole, while soda collects about the nega- 

 tive. Berzelius adopted the following hypothesis : he conceived that 

 every atom had two points or poles, at one of which a quantity of 

 negative electricity might collect, at the other a quantity of positive ; 

 and these quantities not necessarily being equivalent, but one or the 

 other kind predominating in certain atoms might impart to them dis- 

 tinctive properties. Hence he divided bodies into electro-negative 

 (e.g., chlorine) and electro-positive (e.g., hydrogen) by the supposed 

 predominance of one or the other electricity in the atom. The classi- 

 fication by these names has, as a matter of convenience, been more or 

 less retained to the present day ; but the theory itself has lost the 

 importance formerly attached to it. 



A most valuable part of the scientific work of Berzelius was the 

 preparation of a table of the equivalents of the elementary bodies, far 

 more accurate than that which Wollaston had published in 1813. 

 The numbers in Wollaston's table of equivalents (a term first intro- 

 duced by him) were more correct than the atomic weights given by 

 Dalton. But Berzelius extended the table, and by more exact methods 

 of analysis than had before been practised, he arrived at numbers very 

 closely representing those which still more refined researches have 

 since given. In fixing the figures which express the combining pro- 

 portions, any standard whatever that is otherwise convenient may be 

 selected. Thus Wollaston called oxygen 10, while Berzelius adopted 

 i oo as the figure for oxygen. Wollaston's number for hydrogen was 

 1*25, because he considered that water was composed of i equivalent 

 of oxygen -f i equivalent of hydrogen. Berzelius's number for hy- 

 drogen was 6^25, or only half the proportionate value of Wollaston's. 

 The reason was the Swedish chemist's desire to make his system 

 accord with Gay-Lussac's laws regarding water as made up of i atom 

 of oxygen united with 2 atoms of hydrogen. The atomic weight of 

 hydrogen is to the atomic weight of oxygen in Berzelius's system as 

 6 '25 : 100, for this is the ratio of the specific gravities of the two gases. 

 But he considered that hydrogen always entered into combinations 

 in double atoms, and thus H 2 = i2'5 is the equivalent of hydrogen. 

 Nitrogen, chlorine, bromine, and iodine were also considered by Ber- 

 zelius to have equivalents consisting ottwo atoms. In Dalton's system the 

 " atomic weights" were really the proportionate weights in which bodies 



