OZONE AND HYDROGEN PEROXIDE DALTON'S LAW 219 



quantity of the first element, A,.,,, there occur quantities of the second 

 element bearing the same ratio to each other as mr is to qn ; and as //>, 

 r, q, and n are whole numbers, therefore their products are also whole 

 numbers, and this is also expressed by the law of multiple proportions. 

 Consequently the atomic theory is in accordance with and evokes the 

 first laws of definite chemical compounds : the law of definite composi- 

 tion and the law of multiple proportions. 



So, also, is the relation of the atomic theory to the third law of definite 

 chemical compounds, the law of reciprocal combining weights, which is as 

 follows : If a certain weight of a substance C combine with a weight 

 ft of a substance A, and with a weight b of a substance B, then, also, the 

 substances A and B will combine together in quantities a and b (or in 

 multiples of them). This should be the case from the conception of atoms. 

 Let A, B, and C be the weights of the atoms of the three substances, and 

 for simplicity of reasoning let combination proceed in the quantity of one 

 atom. It is evident that if the substance gives AC and BC, then the 

 substances A and B will give a compound AB, or their multiple, A, t B TO . 



Sulphur combines with hydrogen and with oxygen. Sulphuretted 

 hydrogen contains thirty-two parts by weight of sulphur to two parts 

 by weight of hydrogen, which is expressed by the formula H 2 S. Sulphur 

 dioxide, SO 2 , contains thirty-two parts of sulphur and thirty-two parts of 

 oxygen, and therefore we conclude, from the law of combining weights, 

 that oxygen and hydrogen will combine in the proportion of two parts 

 of hydrogen and thirty -two parts of oxygen, or multiple numbers of 

 them. And we have seen this to be the case. Hydrogen peroxide 

 contains thirty-two parts of oxygen, and water sixteen parts, to two 

 parts of hydrogen ; and so it is in all other cases. This consequence of 

 the atomic theory is in accordance with nature, with the results of 

 analysis, and is one of the most important laws of chemistry. It is a law, 

 because it indicates the relation between the weights of substances enter- 

 ing into chemical combination. Further it is an eminently exact law, 

 and not an approximate one. The law of combining weights is a law 

 of nature, and by no means an hypothesis, for let the entire theory of 

 atoms be cast down, still the laws of multiple proportions and of com- 

 bining weights will remain, inasmuch as they deal with facts. They 

 may be guessed at from the sense of the atomic theory, and historically 



presence of an atmosphere round the sun and planets, judging from astronomical observa- 

 tions, may be considered as fully proved. On Jupiter and Mars there may be even 

 distinguished bands of clouds. Thus the atomic doctrine, admitting a finite mechanical 

 divisibility only, must be, as yet at least, only accepted as a means, similar to that means 

 which a mathematician employs when he breaks up a continuous curvilinear line into a 

 number of straight lines. There is a simplicity of representation in atoms, but there is 

 ,110 absolute necessity to have recourse to them. The conception of the individuality of 

 the parts of matter exhibited in chemical elements only is necessary and^trustworthy. 



