1820.] the Atomic Theory. 213 



43, Sulphur. — There are two well known combinations of 

 oxye'en and sulphur, viz. the sulphuric and the sulphurous acids. 

 It has been shown (sect. 17,) that the latter holds two-thirds the 

 quantity of oxygen contained in the former. It has been also 

 shown that the sulphuric acid contains 100 sulphur + 150 oxy- 

 gen (ibid.) Hence, sulphurous acid must contaui two-thnds of 

 150 _ 100 oxygen. Now, if we suppose oxygen to unite with 

 sulphur according to a given arithmetical progression, we shall 

 obtain its lowest combination by constantly taking the common 

 difference from the last lowest term until the difterence is too 

 great to be deducted, or until nothing remains. Thus, two of 

 the terms found are 150 and 100, then- difference is 50 ; there- 

 fore 100 — 50 = 50 will express the next term lower than 100. 

 It is also the lowest for 50, the term last found — 50 common 

 difference = ; therefore, 50 is the quantity of oxygen unitmg 

 with sulphur when the union is the lowest that can be. It is, 

 therefore, a binary, in which 1 atom of oxygen unites with I 

 atom of sulphur, and it will be expressed 100 sulphur + 50 oxy- 

 gen, from which we obtain the proportional weight of an atom 

 of sulphur, as 50 oxygen : 100 sulphur :: 1 weight of an atom of 

 oxygen : 2 weight of an atom of sulphur. For if there be the 

 same number of atoms in 100 by weight of sulphur as in 50 by 

 weio-ht of oxygen, it is evident that the singls atoms themselves 

 musl; bear to each other the same proportion as then- multi- 

 ples do. 



44. Sodium. —When 100 grs. sodium are thrown mto water 

 there is a decomposition of the latter, and 198-30 cubic inches 

 of hydrogen gas are set free ; the temperature being = 60'^, and 

 the barometric pressure = 30 inches. The hydrogen, as a 

 constituent of water, requires half its volume of oxygen, that is 

 198-30 -r- 2 = 99-15 cubic inches, which is the quantity of 

 oxygen that unites with the sodium to form soda. But 99-15 

 cubic inches of oxygen gas weigh 33-6 ; there soda is composed 

 of 100 sodium + 33-6 oxygen, or taking the mean of several 

 experiments 33-3. . 



The peroxide of sodium is composed of 100 sodium + 50 

 oxygen by weight. Now the oxygen in soda (33-3) is to the 

 oxygen in the peroxide of sodium (50) as 2 is to 3 nearly ^ and 

 if 2 and 3 are the lowest proportional terms to which 33-3 and 

 50 can be reduced, the 2 must represent two atoms, and the 3 

 three atoms. The lower numbers than 2 and 3, viz. 1 and 1-5 

 must be rejected, for there can be no fractional part of an hidivi- 

 sible atom ; 2 and 3 are, therefore, the lowest proportionals. 

 This gives soda as a deutoxide, and the peroxide of sodium as a 

 tritroxide. From either of these we may deduce the proportional 

 weight of an atom of sodium. Thus, for the deutoxide, or when 

 1 atom of '.sodium unites with two of oxygen. 



As 33-3 oxygen : 100 sodium :: 2 atoms weight of oxygen : 



