336 Mr. Children's Summary View of [May, 



Article III. 



A Summarij View of the Atomic Theory according to the HypO' 

 thesis adopted by M. Berzelius. By J. G. Children, FRSJ. 



(Continued from p. 193.) 



It is obviously necessary for this purpose, that some sub- 

 stance should be fixed upon, the weight of whose atom may be 

 assumed as unity ; Dalton chose hydrogen for his unit, as the 

 substance of which the smallest weights enter into combination : 

 he has been followed by Davy, Brande, Henry, Phillips, and 

 various other writers ; whilst Wollaston, Thomson, and Berze- 

 lius adopt oxygen as their lowest number, that substance being 

 of all others most universally present in inorganic bodies. On 

 the scale of chemical equivalents Dr. Wollaston reckons oxygen 

 as 10, Thomson considers it as 1, and Berzelius as 100. It is of 

 small consequence which atom be selected fur tlie purpose, or 

 what relative value be assigned to it, whether 1, 10, or 100 ; but 

 whichever be chosen, the weights of the atoms of all other 

 bodies must be expressed in some function of that unit. 



The weight of the atom of any body is easily determined, if 

 we know correctly the composition of one or more of the combi- 

 nations it is capable of forming with any other body, the weight 

 of whose atom has been previously ascertained. Sulphur, for 

 instance, combines with oxygen in several proportions ; in the 

 lowest, 100 parts of sulphur take 50 of oxygen ; in the next, 

 100 ; and in the third, 150 ;* numbers which are in the ratio of 

 1, 2, 3 ; we may, therefore, assume that in the different oxides 

 an atom of sulphur is united successively to 1,2, and 3 atoms of 

 oxygen, and the supposition is supported by various considera- 

 tions of the other combinations of sulphur, as, for instance, 

 those of the sulphurous and sulphuric acids. The lowest com- 

 pound, therefore, may be considered as containing an atom of 

 each element, and if we call that of oxygen 8, we find by a sim- 

 ple proportion that that of the atom of sulphur is 16.f 



This example is sufficient to show the method to be adopted 

 in similar researches, and it is evident that when the weight of 

 the atom of any one body is ascertained, it may be employed 

 for determining that of other bodies. 



The results of a mineral analysis may be calculated on the 

 atomic theory, and the inevitable small errors of experiment 

 corrected by its means. 



* There is a fourth compound formed of an atom of sulphurous acid united to an 

 atom of sulphuric acid, and containing 100 sulphur + 125 oxygen. Its atomic com- 

 position may be stated as just mentioned, or, as consisting of2 atoms sulphur + 5 atoms 

 oxygen. It is not necessary to say more about it in this place. 



'^ I adopt the numbers given by Brande and Pliillips, in which hydrogen is taken as 

 unity. 



