THEORY OF DALTON. 47 



announced by Dalton is, that the constituents of 

 ponderable matter, ichether simple or compound, 

 are capable of combining with each other only in 

 fixed or definite proportions by weight. 



In a practical point of view, this law has been 

 of the highest importance to the manufacturing 

 chemist, independent of its connexion with the 

 whole theory of physical science. 



Passing over the early and imperfect analyses 

 of Dalton, it has been established by the united 

 labours of the most accurate experimenters of 

 modern times, that water is always composed of 

 8 parts by weight of oxygen to 1 of hydrogen ; 

 that common salt is always composed of 36 parts 

 by weight, (in round numbers) of chlorine to 24 

 of sodium ; that carbonate of lime, whether in 

 the form of marble, chalk, or stalactites, is inva- 

 riably composed of 2*2 parts by weight of car- 

 bonic acid, to 28 of lime, &c. 



It was by thus ascertaining the relative pro- 

 portions in which bodies combine chemically by 

 weight, that Dr. Dalton was lead to a perfectly 

 simple method of deducing the relative weights 

 of their ultimate chemical atoms. The theory 

 assumes, that in all cases, the lowest combining 

 proportion of bodies, whether simple or com- 

 pound, represents the weight of its particles ; 

 and that when ever a body combines with another 

 in two or more proportions, the larger is an even 

 multiple by some whole number of the smaller, 



