Biographical Account of the late John Dalton. 87 



attached a number denoting the atomic weight, or\he weight of an atom of 

 each body respectively. Hydrogen, as the lightest, has its atomic weight 

 represented by unity, and oxygen by 7. Every one of his atomic weights 

 is erroneous ; this was the consequence of the want of accurate analyses 

 of compound bodies. 



Dr. Prout first demonstrated that water is a compound of 1 hydrogen and 

 8 oxygen by weight. Therefore, if wo represent water as composed of 

 1 atom hydrogen and 1 atom oxygen, their respective weights will be to each 

 other as 1 to 8. In the same volume Dalton gives the atomic weight and 

 constitution of 37 bodies, but all of them so inaccurate that it would bo 

 needless to state them. In the appendix to the second volume of his System, 

 published in 1810, he has given a few additional compounds, but not 

 more accurate than those given in the preceding volume. Indeed, at that 

 time it was impossible to give the atomic weights accurately, because few 

 or no accurate analyses of compound bodies existed. 



Mr. Dalton represented the atomic weight of hydrogen by unity ; but 

 Dr. Wollaston pointed out the numerous advantages which would result 

 from considering the atomic weight of oxygen to be unity. And this 

 suggestion was adopted by Berzelius in his tables, and has now become 

 almost universal. 



I made a very careful and extensive set of experiments above twenty 

 years ago, from which I deduced that the atomic weights of all bodies are 

 multiples of that of hydrogen. If we denote oxygen by 10, then hydrogen 

 will be 1 # 25, carbon 75, azote 17*5, sulphur 20, phosphorus 20, soda 40, 

 potash 60, &c. These numbers have till lately been almost completely 

 overlooked ; but within these two or three years the subject has been again 

 taken up, and so far as the investigation has gone, my numbers have been 

 verified. Thus Dumas found the atomic weights of hydrogen, carbon, 

 azote, and oxygen, as follows : — 



Hydrogen, . . 0*125 Azote, .... 1*75 

 Carbon, . . . 0*75 Oxygen, .... 100 



Zinc, lead, mercury, silver, have been found. 



Zinc, . . . 4125 Mercury, . . . 125 

 Lead, .... 13 | Silver, .... 13*5 



Potash and soda have been represented on the continent by- 



Potash, . . 5-89916 | Soda, 390897 



But whoever will take the trouble to examine the experiments of 

 Thenard and Gay-Lussac on the oxydizement of potassium and sodium, 

 and my analyses of the salts of potash and soda, must, I conceive, admit 

 that the true atomic weights of these bodies are 



Potash, .... 61 Soda, 4 



