The Genesis of Dalton s Atomic Theory. 351 



According to Roscoe and Harden this latter statement of 

 mine is not correct. My argument rests, they assert, on a 

 confusion between the relative density of the atoms and the 

 relative density of the gases made up of these atoms. 



I cannot allow Dal ton's merits to be set aside in this 

 manner, and I feel at the same time obliged to show that I 

 am not guilty of the mistake attributed to me. 



The atomic theory and the law of equal volumes (law of 

 Avogadro) constitute the basis of scientific chemistry. As it 

 is a matter of importance for everyone to know how the 

 foundation of his house has been laid, I believe the following 

 discussion will not be unacceptable to scientific chemists, 

 especially on account of some new matter considered in it. 

 As Dalton's nomenclature and views differ in several points 

 from those now in vogue, a few explanations will be necessary. 

 The elementary gases consist, according to Dalton, of very 

 small, indivisible particles, called atoms. Each atom is sur- 

 rounded by an atmosphere of heat of from one to two 

 thousand times its own size. Whatever, therefore, may be 

 the shape or figure of the solid atom abstractedly, when sur- 

 rounded by such an atmosphere it must be globular ; bat as 

 all the globules in any small given volume are subject to the 

 same pressure, they must be equal in bulk, and will, there- 

 fore, be arranged in horizontal strata, like a pile of shot (N.S. 

 145) . The volume of the molecule of a gas is equal to the 

 volume of the solid nucleus plus the volume of the atmosphere 

 of heat. Compound molecules result from the juxtaposition 

 of two or more different atoms. A molecule of oxygen is 

 composed of only one atom of oxygen, a molecule of carbonic 

 oxide of an atom of carbon and one of oxygen. Dalton 

 usually employs the word atom ; he calls a molecule of water 

 a molecule of ammonia an " atom of 

 I shall express Dalton's ideas in modern phrase- 

 ology. 



Abbreviations. 

 N.S. stands for : < New System of Chemical Philosophy,' by 



John "Dalton. Manchester, 1808-1810. 

 R.. „ „ 'A New View of the Origin of Dalton's 



Atomic Theory/ by H. E. Eoscoe and 



A. Harden. London : Macmillan & Co., 



1896. 

 0. „ „ Ostwald's Klassiker, No. 8. Leipzig : W. 



Engelmann. 

 Al. „ „ Alembic Club Reprints, No. 2. Edinburgh: 



W. F. Clay. 



