24 



On the Atomic Theory. 



Art. IV. — On the Atomic Theory of Chemistry; by John 

 Finch, M. C. S., &c. 



The Atomic theory, or the system of chemical equiva- 

 lents, is justly considered of the greatest importance, be- 

 cause it has introduced the certainty of mathematical sci- 

 ence into the daily operations of the laboratory. 



By this system, the lowest proportion in which bodies 

 combine is represented by a number attached to each sub- 

 stance, which is called its atomic weight, and it is found by 

 experiment, that bodies combine either in that ratio, or in 

 some multiple of that ratio. 



The following are atomic numbers given by Prof. Brande 

 in his elaborate System of Chemistry : — 



Hydrogen. 

 1. 





Oxygen. 

 8. 





Nitrogen. 

 14. 





Chlorine. 

 36. 





















J Carbon. 

 6. 





Sulphur. 

 16. 





Iodine. 

 125. 





Phosphorus. 

 12. 



These numbers are very similar to those given by Mr. Dal- 

 ton, and by Drs. Thomson, Henry, Wollaston, and Murray. 



All chemists agree in fixing the atomic numbers for oxy- 

 gen and hydrogen by the proportions in which they combine 

 in water, and the equivalent numbers for other substances 

 depend in a great degree upon those which are thus con- 

 ferred. 



Mr. Dalton, in his Elements of Chemical Philosophy, en- 

 deavours to establish as a formula, that where two substan- 

 ces combine in only one proportion, it must be considered as 

 a combination of one atom of each, or, as he expresses it, a 

 binary combination. On this principle, although it is known 

 that water is composed of two volumes hydrogen and one 

 volume oxygen, he considers it as composed of one atom 

 of each, which therefore have to each other the relative 

 numbers 8 oxygen, 1 hydrogen. 



The chemists, whose names are recited above, have, in 

 general, adopted the Daltonian formula ; the following rea- 

 sons may be alleged against its adoption. 



First. — The rule, if correct, cannot apply in the instance 

 of water, because there is another combination known of 

 oxygen and hydrogen, the peroxide of hydrogen, which has 



