86 Biogmphical Account of the late John Dalton. 



the other volume with one volume of carbon, and formed a volume of carbonic 

 acid. Hence carburettod hydrogen is composed of H 2 -f- C condensed 

 into one volume. 



It was this that suggested to him the notions which he entertained 

 respecting the atomic theory. I do not know when he adopted these notions, 

 but when I visited him in 1804 at Manchester, he had adopted them ; and 

 at that time both Mr. Dalton and myself were ignorant of what had been 

 done by Richter on the same subject. 



The ultimate particles of all bodies, in his opinion, consist of atoms 

 incapable of farther division. It is these atoms which combine. These 

 atoms are spherical, and he seems to have thought that they all have 

 the same bulk ; though they differ in weight. We can determine the atomic 

 weight of a body by determining how much of it will combine with another 

 body. He represented the atomic weight of hydrogen by unity, and that 

 of oxygen by 7. 



Water, according to him, is OH 



Olefiant gas is H C H C 



Carburetted hydrogen H C H 



So that if we take an atom of carbon from olefiant gas we convert it 

 into carburetted hydrogen, and if we add an atom of carbon to carburetted 

 hydrogen, we convert it into olefiant gas. 



These two gases constituted the only example of the combination of 1 

 and 2 atoms of one substance, with an atom of another. I furnished him 

 with another example in the oxalate and binoxalate of strontian. The 

 first salt is a compound of 1 atom oxalic acid with 1 atom of strontian, 

 and the second, of 2 atoms of oxalic acid with 1 atom of strontian. Dr. 

 Wollaston furnished him with another in oxalate, binoxalate, and quad- 

 roxalate of potash. 



1. 1 atom Oxalic acid with 1 atom Potash. 



2. 2 atoms 1 atom Potash. 



3. 4 atoms 1 atom Potash. 



These were the data from which he deduced what is now called the 

 Theory of Atomic Weights. 



At the end of the first volume of his New System of Chemical Philosophy, 

 published in 1808, there is an engraving, on which are represented the 

 symbols by which the different simple bodies are distinguished. He gives 

 20 symbols, each consisting of a circle, with some internal mark of dis- 

 tinction. Oxygen is represented by a circle, hydrogen by a circle with a 

 dot in the centre, azote by a circle with a perpendicular line, carbon 

 by a circle blackened within, 9. the metals by circles within which the 

 first letter of the name of the metal is given ; thus, (i), (z), represent an 

 atom of iron and zinc respectively. He gives 20 symbols, and shows how 

 2, 3, 4, 5, 6, and 7, of these atoms may be united together so as to form 

 new compound bodies. To each of these 20 simple bodies, he has 



