CHEMISTRY OF THE NINETEENfH\CENT~ 



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certain classes of facts which have since attracted the attention of 

 chemists. Many of the laws relating to matter iri Ae/ gaseous sVa'te. 

 are known, and the uniformities they present are very strik)rjg when 

 compared with diversities presented by liquids and solids. '/H^nce 

 some have designated the gaseous as the perfect state of matter, Thej 

 hypothesis of Avogadro, suggested by certain uniformities in the beha- 

 viour of different gases, has the beautiful simplicity which distinguishes 



FIG. 306. JOHN DALTON. 



many fertile theories. The deductions from it have an harmonious 

 consistency in both chemistry and physics. Dalton rejected this hypo- 

 thesis partly on account of difficulties arising from his ideas concern- 

 ing the atmospheres of caloric. 



" In prosecuting my inquiries into the nature of elastic fluids, I soon 

 perceived it was necessary, if possible, to ascertain whether the atoms 

 or ultimate particles of the different gases are of the same size or 

 volume, in like circumstances of temperature and pressure. By the 

 size or volume of an ultimate particle I mean in this place the space 

 it occupies in the state of a pure elastic fluid : in this sense the bulk 



