118 Review of Dr. Thomson 



are not yet all agreed about its weight. 2. Hydrogen, so far as 

 we know at present, combines with but few of the other simple 

 bodies ; while oxygen unites with them all, and often in various 

 proportions. Consequently, very little advantage is gained by 

 representing the atom of hydrogen by unity ; but a very great 

 one, by representing the atom of oxygen by unity. For it re- 

 duces the greater number of arithmetical operations respecting 

 these bodies to the addition of unity ; and we see at once, by a 

 glance of the eye, the number of atoms of oxygen which enter 

 into combination with the various bodies. Thus, if the atom of 

 manganese be represented by 3.5, and the weight of the various 

 oxides of that metal be as follows : 



1. Suboxide 4 4. Tritoxide 5.5 



2. Protoxide 4.5 5. Manganesious acid 6.5 



3. Deutoxide 5 6. Manganesic acid 7.5 

 It is obvious at once tfcat the 



Suboxide contains J atom ox. Tritoxide 2 atom ox. 



Proxide 1 Manganesious acid 3 



Deutoxide lj Mangenesic acid 4 



Whereas, if we were to make the atom of hydrogen unity, 

 these weights would be as follows : 



Manganese 28 Tritoxide 48 



Suboxide 32 Manganesious acid 56 



Protoxide 36 Manganesic acid 64 



Deutoxide 40 



Numbers, which would not suggest the number of atoms of 

 oxygen contained in each, with the same facility *." 



The first reason given by Dr. Thomson applies with equal 

 force to oxygen, for its relation in atomic weight to other bodies 

 is little better known than that of hydrogen to them. The pro- 

 portional weights of these rival elements are always inferred 

 from the composition of water ; and whatever relation be dis- 

 covered between them, it will pervade the whole system of 

 bodies which have for a constituent either hydrogen or water. 

 In Mr. Dalton's original numbers, published in 1808, the atomic 

 relation of hydrogen to oxygen in water is 1 to 7 ; and therefore 

 to reduce all the numbers to the oxygen unity, they have only to 

 be divided by 7. No error will be introduced into the resulting 

 numbers, by having taken the hydrogen unity, provided the 

 analyses of the oxides and oxygen acids have been exact. Again, 

 if water be supposed to consist of 1 part hydrogen to 7\ oxygen, 

 as on Dr. Wollaston's scale, surely this synoptic table would not 

 have its accuracy affected by reducing the numbers to a hydro- 

 gen unity ; for the relations of oxygen to the other bodies, 

 being deduced from their proper authorities, would stand as 

 before. 



* Historical Introduction, p. 14. 



