XXII 

 JOHN DALTON 



I 766- I 844 



John Dalton, son of a weaver, was born in Cumberland, England, 

 September 5, iy66. After an early life spent in teaching in ele- 

 mentary schools, in //pj he became a teacher of mathematics and phi- 

 losophy at Nezv College, Manchester. He began his researches into 

 the combination of gases in 1800 and discovered that gases expanded 

 equally iinth the same pressure and heat. He announced his discov- 

 ery in a paper read before the Manchester Society in 1801. From 

 further experiments he derived his theory that gases combined with 

 one another in definite proportions, and evolved his atomic theory to 

 explain the results. Awarded the King's medal in 1822, he was fur- 

 ther honored by a pension granted in 18 j^. He died May 2/, 1844. 



THE ATOMIC THEORY * 



There are three distinctions in the kinds of bodies, or three states, 

 which have more especially claimed the attention of philosophical 

 chemists ; namely, those which are marked by the terms elastic fluids, 

 liquids, and solids. A very familiar instance is exhibited to us in 

 water, of a body which, in certain circumstances, is capable of assum- 

 ing all the three states. In steam we recognize a perfectly elastic fluid, 

 in water a perfect liquid, and in ice a complete solid. These observa- 

 tions have tacitly led to the conclusion which seems universally 

 adopted, that all bodies of sensible magnitude, whether liquid or solid, 

 are constituted of a vast number of extremely small particles, or atoms 



* From a note entitled On the Constitution of Bodies which Dalton wrote 

 and had incorporated in Thomas Thompson's System of Chemistry (3d edi- 

 tion, 1807). 



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