58 HISTORY OF CHEMISTRY. [LECTURE IV. 



accurate with respect to this standard. The atomic weight of 

 carbon had in reality only been found to be a multiple or a 

 submultiple of 5.4. Dalton himself does not appear to have 

 been aware of this arbitrary character of his numbers. 



In spite of this, his theory met with very general re- 

 cognition, and chemists were astonished at the simplicity with 

 which it explained all the regularities which had been dis- 

 covered immediately before. With the rapid progress that the 

 science was at that time making, some new support was 

 necessary. In order to avoid being left behind it was essential 

 to possess a general point of view from which the isolated facts 

 and the different regularities could be conveniently surveyed. 

 It was soon to be shown that this theory was capable of stand- 

 ing the test ; that it was not only sufficient to connect the 

 known phenomena, but that laws which were only discovered 

 subsequently could also be explained by means of it. This 

 holds especially for the law of gaseous volumes, which Gay- 

 Lussac discovered in 1808, a few months after the appearance 

 of Dalton's ingenious book. 



As early as 1805, Humboldt and Gay-Lussac, on the 

 occasion of their joint investigation of the composition of the 

 air, had determined anew the proportions by volume in which 

 hydrogen and oxygen combine. 25 They found slight differ- 

 ences from the earlier observations, and arrived at the highly 

 interesting result that water is produced by the condensation of 

 2 volumes of hydrogen and i of oxygen ; while Meusnier and 

 Lavoisier 26 had found 23 volumes of hydrogen and 12 of oxy- 

 gen, and Fourcroy, Vauquelin, and Seguin 27 had found 205.2 

 of hydrogen for 100 of oxygen. 



Three years later, Gay-Lussac extended his experiments to 

 other gases. 28 He had previously observed the law (often called 

 after him) of the uniform expansion of gases with increase of 

 temperature. 29 He was also familiar with the so-called law of 



23 Journ. de Phys. 60, 129. 26 Lavoisier, Oeuvres. 2, 360. ^ Ann. 

 Chim. 8, 230 ; 9, 30. w Mem. d'Arcueil. 2, 207. 29 Ann. Chim. 43, 

 137- 



