36 On the Daltonian Theorrj of [July, 



For it has been ascertained, I think, with precision, that water 

 is composed of 100 measures of oxygen gas, and 200 measures 

 of hydrogen gas. Now the specific gravity of these gases are as 

 follows : — 



Oxygen 1-104 



Hydrogen 0-073 



Hence water is composed by weight of 



Oxygen 7-56 



Hydrogen 1-00 



From this coincidence we are entitled to conclude that water 

 is formed by the union of an atom of oxygen to an atom of 

 hydrogen. This very important conclusion is supported by other 

 considerations. Oxygen and hydrogen have never been made to 

 combine in any other proportion than that in which they exist in 

 water. Hence this proportion must be that which unites most 

 readily, and with the greatest force. Now as the atoms of 

 hydrogen repel each other, as is the case also with the atoms of 

 oxygen ; and as hydrogen is attracted by oxygen ; it is obvious 

 that when they are mixed equably, as is the case when 200 

 measures of hydrogen gas, and 100 measures of oxygen gas, are 

 put into a tube, and fired by electricity, they will most readily 

 unite atom to atom. This, though not in itself decisive, is a 

 corroborating circumstance. It follows from it that a given bulk 

 of hydrogen gas contains only one-half the number of atoms 

 that exist in the same bulk of oxygen gas. 



6. Knowing the weight of an atom of oxygen and of an atom 

 of hydrogen, we have it in our power to deteimine the weight 

 of an atom of the other substances which unite with oxygen, or 

 with hydrogen, or with both. For example, 100 parts of sul- 

 phur unite with two proportions of oxygen, the first consisting 

 of 100, the second of 150 parts, both in weight. Here the 

 proportions of oxygen being to each other as the numbers 1, 1^, 

 or as 2, 3, it is reasonable to suppose that the first portion repre- 

 sents two atoms of oxygen, and the second three atoms ; and 

 that there is another compound, consisting of sulphur united 

 with one atom of oxygen, not yet discovered. If this supposi- 

 tion be reasonable, it follows, that the weight of sulphur which 

 enters into these combinations represents an atom of that sub- 

 stance. Therefore 100 represents an atom of sulphur, and 100 

 two atoms of oxygen ; so that an atom of sulphur, it appears, is 

 just double the weight of an atom of oxygen. 



We have it in our power to verify this reasoning, by means of 

 the combinations which sulphur makes with hydrogen. It has 

 been ascertained that 100 measures of hydrogen gas, when they 

 unite with sulphur, do not alter their bulk, but merely their 



