48 THEORY OF D ALTON. 



as 2 to 1, 3 to 1, 4 to 1, &c. ; fractional parts 

 seldom occurring in well ascertained cases. 



By inspecting the following Table, it will be 

 seen that the smallest combining ratio of oxygen 

 is 8, compared with hydrogen as unity ; and that 

 when it combines with other elements in larger 

 proportions, they are 16, 24, 32, 40, or some 

 multiple of 8. Chlorine combines with mercury 

 in the ratio of 36, as in chloride of mercury, 

 (calomel), or of 72, as in the bi-chloride of mer- 

 cury, (corrosive sublimate) and so of carbon, 

 hydrogen, and other elements. 



I have adopted the atomic numbers employed 

 by the majority of British chemists in preference 

 to those of Berzelius, chiefly with a view of avoid- 

 ing the inconvenience of fractions. I have also 

 chosen hydrogen as a standard of comparison 

 for the same reason. Berzelius has selected oxy- 

 gen 100.00 as a standard, on account of its great 

 abundance, and the vast variety of combinations 

 which it forms ; while Thomson and Ure have 

 employed oxygen as unity, by which hydrogen 

 is rendered 8 times less; or 0.125, carbon 0.75, 

 sulphur 2, mercury 25 or 12^, chlorine 4.5, and 

 so on ; both of which are unavoidably attended 

 with fractions that are difficult to remember. 



Dr. Wollaston employed the terms chemical 

 equivalent, and Sir Humphrey Davy combining 

 proportion, to denote the atom of Dalton. I shall 

 generally use the term atom, or particle, as indi- 



