THEOKY OF DEFINITE PROPORTIONS. 287 



bodies; these views being suck as to include both these two rules in 

 their most general form, and further, the rule, at that time still more 

 new to chemists, of multiple proportions. He conceived bodies as 

 composed of atoms of their constituent elements, grouped, either one 

 and one. or one and two, or one and three, and so on. Thus, if C 

 represent an atom of carbon and one of oxygen, will be an 

 atom of carbonic oxide, and C an atom of carbonic acid ; and 

 hence it follows, that while both these bodies have a definite quantity 

 of oxygen to a given quantity of carbon, in the latter substance this 

 quantity is double of what it is in the former. 



The consideration of bodies as consisting of compound atoms, each 

 of these being composed of elementary atoms, naturally led to this law 

 of multiple proportions. In this mode of viewing bodies, Mr. Dalton 

 had been preceded (unknown to himself) by Mr. Higgins, who, in 1789, 

 published 4 his Comparative View of the Phlogistic and Antiphlogistic 

 Theories. He there says, 6 " That in volatile vitriolic acid, a single ulti- 

 mate particle of sulphur is united only to a single particle of dephlo- 

 gisticated air ; and that in perfect vitriolic acid, every single particle 

 of sulphur is united to two of dephlogisticated air, being the quantity 

 necessary to saturation ;" and he reasons in the same manner concern- 

 ing the constitution of water, and the compounds of nitrogen and 

 oxygen. These observations of Higgins were, however, made casually, 

 and not followed out, and cannot affect Dalton's claim to original merit. 



Mr.' Dalton's generalization was first suggested 8 during his examina- 

 tion of olefiant gas and carburetted hydrogen gas ; and was asserted 

 generally, on the strength of a few facts, being, as it were, irresistibly 

 recommended by the clearness and simplicity which the notion pos- 

 sessed. Mr. Dalton himself represented the compound atoms of bodies 

 by symbols, which professed to exhibit the arrangement of the ele- 

 mentary atoms in space as well as their numerical proportion ; and he 

 attached great importance to this part of his scheme. It is clear, how- 

 ever, that this part of his doctrine is not essential to that numerical 

 comparison of the law with facts, on which its establishment rests. 

 These hypothetica 1 configurations of atoms have no value till they are 

 confirmed by corresponding facts, such as the optical or crystallii>fl 

 properties of bodies may perhaps one day furnish. 



Turner's Chem. p. 217. P- 36 and 37. 



Thomson, vol. ii. p. 291. 



