68 RELATION OF ATOMS TO VOLUMES. 



mass of phenomena, for which no satisfactory 

 reason can be assigned. 



In regard to several bodies termed elementary, 

 chemists have not yet been able to determine 

 whether we have obtained their true atomic 

 weights, or only multiples or submultiples of 

 them. At one time, it was supposed by Ampere 

 and Dumas, that equal volumes of all gases and 

 vapours, simple or compound, contain exactly 

 the same number of atoms. In order to sustain 

 this hypothesis, so beautiful from its simplicity, 

 Dumas imagined that when chlorine unites che- 

 mically with hydrogen to form hydrochloric acid 

 gas, their atoms undergo a division, by which 2 

 atoms of the acid are formed out of one of each 

 of its elements. It is needless to insist, that these 

 hypotheses have not been found in accordance 

 with established facts. 



That equal volumes of all gases contain equal 

 numbers of atoms was inferred, first, from the 

 circumstance that all gaseous bodies are equally 

 expanded by the same additions of caloric, the 

 pressure being equal : and secondly, from the 

 supposed fact, (which has been termed the law of 

 Mariotte), that the volume of any gas whatsoever, 

 diminishes in proportion to the pressure exerted 

 upon it, the temperature being equal. It was 

 maintained, that if the number of atoms in each 

 gas were not the same, the diminution of volume 

 under the same pressure ought also to vary. 



