170 ATTRACTION. 



THEORY OF ATOMS. 



For a complete view of this curious and interesting speculation, re- 

 course must be had to the writings of Higgins^ Dalton, Berzelius, 

 Thomson and others.* 



In the sketch that has been given of definite proportions, I have in- 

 tentionally avoided the use of the word atom, because it may be mis- 

 understood, and may lead beginners to confound facts with hypothe- 

 sis. The doctrine of definite and multiple proportions is established 

 on the basis of experiment, and is fully confirmed both by analysis 

 and calculation. 



The expressions, combining weight, combining quantity, or combin- 

 ing proportion, and chemical equivalent, all mean the same thing ; and 

 it may be added, that atom, and atomic constitution and atomic weight, 

 are used by most writers in the same sense. The atomic hypothesis, 

 first suggested by Mr. Higgins, (1789,) was so fully detailed and illus- 

 trated by Mr. Dalton, in his Chemical Philosophy, that the theory is 

 usually considered as his. It is ingenious and beautiful, and there 

 can be no reasonable doubt that matter has an atomic constitution ; 

 but, that it is such as the atomic theory now in discussion supposes, 

 although highly probable, cannot be demonstrated ; and it is there- 

 fore important for the student to be able to distinguish it, or any other 

 atomic theory that may be proposed, from the luminous and demon- 

 strated verity of definite and multiple proportions. 



(AM.) If we assume that bodies, in the combination in which they 

 exist in the smallest proportions, unite atom and atom, then their re- 

 lative weights in those cases, will represent those of their atoms. 

 This assumption is the foundation of the atomic theory. 



(Hi.) There being no combination in which hydrogen is known to 

 exist in smaller proportion than in water, and the specific gravity of 

 hydrogen to oxygen being as 1:16, if these elements unite atom to 

 atom, and a volume of each represents an atom, then the relative 



3. " The sulphur of the acid is just double the oxygen of the base." 



4. The acid itself is just five times as much as the oxygen of the base. 



Metallic sulphurets often contain one proportion of each element, and when con- 

 verted into a salt, the sulphuric acid and the protoxide will be exactly in the propor- 

 tion for forming a neutral sulphate of a protoxide. 



In the carbonates, the oxygen of the acid is generally double that of the base, and 

 a similar mode of reasoning is applicable to the various genera of salts ; but no con- 

 stant ratio exists between the quantity of oxide and that of the acid, or of the oxygen 

 in the acid, because the combining weights of the metals themselves are different. 

 All these facts are arranged naturally under Mr. Dalton's principle of multiple pro- 

 portions. 



An attempt has been made to extend the same views to the constitution of miner- 

 als. See Ann. of Philosophy, N. S. Vol. IX, Mr. Children. 



* See Henry, 10th London Ed. Vol. I, p. 42. Thomson's First Principles of 

 Chemistry, and Turner and Murray. 



