1825.5 Dr. ThomsorCt'FM Principle of Chemistry, 139 



some process which we have not discovered, decimals al'e more 

 easily remembered than whole numbers, and numerous figure* 

 than few. 



With respect to the decimals included in those numbers 

 which result from the adoption of oxygen as unity, Dr. Thomson 

 observes : " Now surely it will not be said that the fractional 

 numbers are more unwieldy or more unmanageable than the whole 

 numbers ; while in all cases of whole numbers, the advantage on 

 the s'de of the latter method is very great. Thus if hydrogen be 

 unity, the atom of uranium is 208, while if oxygen be unity, it is 

 only 26." 



Let it be granted for a moment that provided we have to remem- 

 ber a certain number of figures, it is indifferent whether they are 

 decimals or whole numbers ; and let us then examine in which 

 mode the greater facihty is obtained. Dr. Thomson's third table 

 contains 408 substances hydrogen; being 1, 319 of these are 

 represented by two figures, and 89 by three, and consequently 

 no one by any greater number ; but oxygen being unity, we 

 have 58 bodies represented by "one figure, 104 by two, 99 by 

 three, 143 by four, and 4 by five figures. It will also appear 

 that of 246 substances represented by three, four, or five figures, 

 oxygen being unity, 200 are represented by two figures only, 

 when hydrogen is the standard of comparison. The sixth table 

 contains the atomic weight of 646 bodies ; of these, 262 are 

 represented by four, five, and 1 by six figures, of which not one 

 would exceed three figures, hydrogen being 1. 



These statements are, we think, sufficient to settle the ques- 

 tion of facility. But in conversation, let any chemist inquire of 

 another by what number he represents any given substance-*- 

 let it be nitrate of manganese ; if oxygen be unity, the answer 

 will be 19*125. If hydrogen be the standard, the answer will be 

 153. Now this is not an extreme case ; there are many such as 

 will be readily imagined from what has been stated. 



The author proceeds to the consideration of the relative and 

 absolute weight of oxygen and hydrogen gases, and the compo- 

 sition of water. He discusses the question whether that fluid, 

 according to the views of Sir H. Davy and Professor Berzelius, 

 is a compound of 1 atom of oxygen and 2 atoms of hydrogen, as 

 indicated by their respective volumes, or constituted of one 

 atom of each of its elements. We need hardly observe that the 

 author coincides with the views of most other chemists in 

 adopting the latter opinion. 



Several well imagined and executed experiments are related, 

 all of which tend to confirm the opinion that an atom of hydro- 

 gen being 1, that of oxygen is 8, and of water consequently^^. 

 This part of the subject had indeed been so completely set%d 

 in our opinion by the previous researches of the author ..^F^d 

 others, that it was scarcely requisite to perform fresh experi^ 



