(c) Chemical compounds consist of "compound atoms" 

 (nowadays called molecules), in which the atoms 

 of the elements forming each compound are united 

 in fixed, whole number, ratios. 

 The laws of chemical combination, determined ex- 

 perimentally, showed that all chemical compounds were 

 formed by the combination of the different elements in 

 definite proportions by weight. Thus, in carbon monoxide, 

 it was always found that there were 16 parts by weight 

 of oxygen to 12 parts of carbon, in whatever manner 

 carbon monoxide was prepared. In carbon dioxide, the 

 combining ratio was 32 parts by weight of oxygen to 12 

 parts of carbon, i.e. there was precisely twice as much 

 oxygen combined with a given weight of carbon in car- 

 bon dioxide as was combined with the same weight of car- 

 bon in carbon monoxide. It was thus clear that the units 

 in which oxygen and carbon existed were perfectly defi- 

 nite in weight, and that carbon monoxide was composed 

 of "compound atoms" each of which consisted of one car- 

 bon and one oxygen atom, which had relative weights of 

 12 and 16 respectively. Similarly, carbon dioxide was 

 composed of "compound atoms" consisting of one car- 

 bon to two oxygen atoms, giving the relative proportions 

 of 12 to 32 parts by weight. Every part of any piece of 

 a pure chemical element has the same chemical properties, 

 agreeing with Dalton's first postulate. And Dalton's sec- 

 ond postulate is proved to be true by the experimental 

 law of the conservation of mass. There was no way of 

 detecting single atoms until long after Dalton's great theory 

 was proposed, but the proofs which he gave were conclusive 

 regarding the real existence of atoms. We can detect 

 individual atoms and measure their masses and diameters, 

 and it is found that they conform to Dalton's postulates. 



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