304 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



This law recognises that elements may combine together 

 in different proportions, but adds (i) that each of these 

 proportions is fixed -and (2) that the different fixed propor- 

 tions are not independent of one another, but are related in 

 the simplest possible way. Thus, if hydrogen and oxygen 

 unite together in the ratio i : 8 to form water, they may 

 also unite in the ratio 2:8, 3 : 8, 4 : 8, or i : 16, i : 24, 

 1:32 (or, generally, in the ratio n x i : m x 8, where n and 

 m are whole numbers) in forming other compounds ; but 

 they cannot combine together in intermediate ratios such as 

 1*107 : 8 or i : 7*823, which are wholly independent of the 

 ratio in which they are present in water. Berthollet, who 

 claimed "that a substance may combine in all proportions 

 with another on which it acts by a reciprocal affinity " 

 (Journ. de Physique, 1805, 60, 347), had no place for 

 the law of multiple proportions. Proust, who recognised 

 the existence in many cases of two or more fixed proportions, 

 and especially of a fixed maximum and minimum, might 

 easily have discovered the law of multiple proportions if his 

 analyses had been more exact. Thus, in the case of iron 

 and sulphur he gave the proportions as 



sulphur to iron = 60 : 100, minimum 

 ,, =90 : 100, maximum 



These two proportions are in the simple integral ratio 2:3; 

 but as the actual proportions are 57 : 100 and 114 : 100, 

 ratio 1:2, it is not surprising that his measurements as a 

 whole did not disclose any simple relationship between the 

 maximum and minimum proportions. 



j The law of multiple proportions was therefore first dis- 

 covered by Dalton as a direct and obvious deduction from 

 fiis atomic theory. No formal statement of the law was 

 made, but several cases were quoted to which the law 

 can be applied, e.g. the three oxides of nitrogen in which 



