92 HISTORY OF CHEMISTRY. [LECTURE VI, 



finds confirmation in Gay-Lussac's rule ; and, by measuring 

 the volumes, Berzelius can here determine the number of 

 atoms which mutually combine with one another. For example, 

 since two volumes of hydrogen unite with one volume of oxygen, 

 water consists of two atoms of hydrogen and one atom of 

 oxygen. He cannot conceive how anyone can be of a different 

 opinion, and he engages in controversy with Thomson, who 

 only assumes half as many atoms in one volume of hydrogen 

 as in one volume of oxygen. 



" It has been assumed that water is composed of an atom 

 of oxygen and an atom of hydrogen ; but since it contains two 

 volumes of the latter gas for one of the former, it was concluded 

 that in hydrogen and in inflammable substances generally, the 

 volume weighs only half as much as the atom, while in oxygen, 

 volume and atom have the same weight. As this is only an 

 arbitrary assumption, the accuracy of which cannot even be 

 tested, it appears to me much simpler and more conformable 

 with probability to assume the same relation of weight between 

 the volume and the atom in the combustible substances as in 

 oxygen ; because there is nothing which should make us 

 suppose a difference between them. If water is regarded as 

 composed of two atoms of radical and one atom of oxygen, 

 then the corpuscular (atomic) and the volume theories coincide, 

 so that their difference only consists in the state of aggregation 

 in which they present the substances to us." 17 



It must be mentioned that Berzelius does not extend to the 

 compound gases, his view as to the identity of volume and 

 atom, but considers that the atoms of these neither occupy the 

 same space as the atoms of the elements nor show uniformity 

 of volume amongst themselves. That this is so, follows from 

 his atomic weight estimations. With him, H = i = i volume or 

 i atom of hydrogen ; H. 2 O =18 = 2 volumes or i atom of water ; 

 73 = 4 volumes or i atom of hydrochloric acid, etc. 18 



17 Lehrbuch. 3, part I, 44-45. 18 It is true that he calls HC1 = 36.5 an 

 atom of hydrochloric acid and says HG4 is the double atom (see Lehrbuch), 

 but for the most part he actually employs the formula Hl. I return to this 

 again, however, farther on. 



