ON MR. DALTON's PRINCIPLE OF COMBINATION. -^^ 



pothesis is at present unsupported by any evidence, yet it 

 implies nothing contradictory to reason or experience; so 

 that, if it appear that there areany number of facts which co- 

 incide with it, or that are conveniently explained by it, they 

 muat be considered as forminoj an indirect arj<unaent in its 

 favour. Now if we admit the truth of tlie hypothesis, so far 

 as respects the union of the two elements atom by atom, a 

 necessary consequence is, that the compound will be either 

 hinary*y or that the number of atoms in the substance 

 which exists in the greatest quantity will be some multiple 

 of the atoms existicig in the smaller quantity. I will take Compounds of 



the example of sulphur and oxij;en. These bodies unite in sulphur and 



. . . oxigen. 



three different proportions, of which one must be binary^ 



i. e. 100 atoms of sulphur and 100 atoms of oxigen will 

 unite and form 100 atoms of some compound, which com- 

 pound we might a priori suppose would be that in which 

 the strongest affinity is exerted between the two elements. 

 In all the other compounds it necessarily follows, that the 

 number of atoms which exist in the largest quantity, must 

 be either as 200, 300, 400, or some multiple of ICO ; for it is 

 obvious, that the substances could not combine atom by- 

 atom, were the greater number of atoms to exist in the rati* 

 of 120, 150, or in any quantity intermediate between the 

 centesimal numbers. It seems the most natural to regard 

 the sulphuric acid as the ftiwary compound of sulphur and 

 oxigen, or that 100 atoms of sulphur and 100 atoms of oxi- 

 gen form 100 atoms of sulphuric acid. According to the 

 most accurate experiments, the respective weights of the 

 component parts of sulphuric acid are 100 parts of sulphur 

 to 136*5 parts of oxigenf, therefore the weight of an atom 

 of sulphur will be to the weight of an atom of oxigen as I 

 to 1*365, or nearly as 3 to 4. Let us now try how this sup- 

 position will coincide vvith the composition of the next com- 

 pound of sulphur and oxigen, sulphurous acid, 100 parts of 

 which are stated, upon the respectable authority of Dr. 



• The word UnaTy is here, and in al! the ether parts of thi<i paper, em- 

 ployei in the sense which Mr Dalton assigns to it; but it is obvious, how- 

 much confusion may be introduced by the circumstance of there being two 

 different significations applied to the* same scienlific term, 



fKlaproth, Gfthlen'fJwur. V. 109. 



Thomson^ 



