1818.] Definite Proportions in Chemical Combinations. 37 



specific gravity. Hence, in order to determine the constituents 

 of sulphureted hydrogen gas with perfect accuracy, we have 

 only to ascertain correctly the specific gravity of hydrogen gas 

 and of sulphurcted hydrogen gas. Now 



100 cubic inches of hydrogen gas weigh 2*230 gr. 



100 cubic inches of sul-phureted hydrogen . . .35-890 



Hence it follows that sulphureted hydrogen gas is composed of 



Hydrogen - 2-23 or 1-00 



Sulphur 33-66 15-09 



This shows us that if sulphureted hydrogen gas is composed of 

 an atom of hydrogen united to an atom of sulphur (and hardly 

 any other supposition seems admissible), then if an atom of 

 hydrogen weigh 1, an atom of sulphur will weigh 15-09. The 

 combination of oxygen and sulphur gave us 15-12 for the weight 

 of an atom of sulphur. Thus the two processes of reasoning 

 lead to the same conclusion, since the difference between 15*09 

 and 15-12 is only —„%„• This is as near a coincidence as it is 

 possible to obtain from chemical experiments, where absolute 

 precision, from the nature of our processes, is impossible. 



By a similar mode of reasoning, we may determine with 

 considerable accuracy the weight of an atom of azote, phospho- 

 rus, carbon, and the metals. It would be tedious to state the 

 methods here at full length ; but some of the most important of 

 them will be given afterwards. 



It is hardly necessary to observe, how very powerfully a parti- 

 cular conclusion is confirmed when we arrive at it by different 

 processes. This advantage we have in full perfection when we 

 set about determining the weight of the atoms of the simple 

 substances. In most cases we come to the same conclusion by 

 two, three, or four different methods. These coincidences, I 

 think, could not exist, unless the conclusion were well founded. 

 7. I shall terminate this part of the subject with Mr. Dalton's 

 canons for the combination of the atoms of bodies with each 

 other. They are very ingeniously contrived, and their truth, I 

 conceive, will be readily admitted by every person who pays due 

 attention to the subject: — 



1st. When only one combination of two bodies can he ob- 

 tained, it must be presumed to be a binary* one, unless some 

 cause appear to the contrary. 



2d. When two combinations are observed, they must be pre- 

 sumed to be a binary and a ternary. 



• By binary, Mr, Dnlton mraiot a compound of one atom of one body with 

 one atom of another ; l>y ternary, a compound of oue atom of one body with 

 two atouib of iinoiliiT ; and t,u on. 



