16 HISTORICAL INTRODUCTION. 



Protoxide . . 36 



Deutoxide , . 40 



Tritoxide . . 48 



Manganesous acid . 56 



Manganesic acid . 64 



Numbers, which would not suggest the number 

 of atoms of oxygen contained in each, with the 

 same facility. 

 But the ra. 3. All the knowledge that we are likely ever 



tins should 



. . .. . 



to acquire or the atomic weights of bodies, is 

 bie. si tl ~ merely the ratios of these weights. Now, it is ob- 

 vious, that ratios are much more easily observed, 

 and much more easily employed, the smaller the 

 numbers are, by which they are denoted. Thus 

 the ratio of 38741 to 116223 is the same as that 

 of 1 to 3. But how very inconvenient would 

 the great number of figures be, compared with 

 the simple number 1 : 3. It is therefore highly 

 important in chemistry, that the atomic weights 

 of bodies should be represented by the smallest 

 possible numbers. Now, when we make the 

 atom of oxygen unity, the atomic weights of all 

 bodies are represented by numbers eight times 

 less than they would be if the atom of hydrogen 

 be unity. It has been represented by some 

 persons, in favour of the atom of hydrogen being 

 unity, that in that case the atomic weight of 

 every body is a whole number; whereas, when 

 oxygen is the unity, fractions are frequently 

 unavoidable. And these fractions, it is said, ren- 



