352 Dr. H. Dab us on the Genesis of 



D. stands for i Ueber einige Fundamentals'atze der Che- 

 mie, insbesondere das Dalton- Avoga- 

 dro'sche Gresetz ' ; von Dr. Heinrich 

 Debus. Cassel : Qustav Klaunig, 1894. 



M „ „ Molecular Weight. 



S „ „ Specific gravity. 



M/S ,, „ Molecular volume. 



Division of numbers is expressed thus, M/S: 



|f =M/S. 



(p. ...) page ... in this paper. 



The empirical law that equal volumes of different gases 

 contain, at normal temperatures and pressure, an equal num- 

 ber of molecules will be represented by the symbols M/S = C. 



1. Dalton's Atomic Theory. 



The opinion used to be common amongst chemists * that 

 Dalton had originated the idea of indivisible particles (atoms) 

 for the explanation of the law of multiple proportions. This, 

 however, is not the case. The idea that the objects of ob- 

 servation are aggregates of exceedingly small indivisible par- 

 ticles is older than science itself ; it is attributed to a Phe- 

 nician philosopher, Moschus, living at Sidon at about 1100 B.C. 

 (D. 35) . His views, developed by the Greeks, were forgotten 

 after the destruction of the Roman empire, but resuscitated 

 by Grassendi about the middle of the 17th century. Boyle, 

 who called the atomic hypothesis the Phenician philosophy f , 

 applied it to the explanation of chemical phenomena, and 

 Newton to the explanation of Boyle's law. Also the chemists 

 of the last century employed the atomic doctrine for the 

 illustration of chemical change (D. 38-10). Dalton, who 

 seems to have obtained the idea of atoms from Newton (R. 13, 

 123), applied it, almost from the beginning of his scientific 

 career, to the explanation of physical phenomena, such as 

 diffusion, absorption, and expansion. In 1803 he discovered 

 a method how to determine the relative weight of atoms, and 

 added to the atomic philosophy a series of principles. The 

 group of principles so added by Dalton I propose to call 

 Dalton's " atomic theory/' 



The main points are :— 



* Liebig, Handbuch der Chemie, Heidelberg 1843, p. 65. 

 t 'The Works of the Right Hon. Robert Boyle.' London, 1744, 

 vol. i. p. 228. 



