138^ Anal^es of Booku [AuG« 



Article X. 



Analyses of Books. 



An Attempt to establish the First Principles of Chemistry by 

 Experiment. By Thomas Thomson, MD. FRS. Regius Pro- 

 fessor of Chemistry in the University of Glasgow, &c. In 

 Two Volumes, 8vo. 1825. 



This work may be considered under two different points of 

 view; first, as a collection of the principal facts upon which the 

 important doctrine of definite proportions or atomic theory is 

 founded; and, secondly, as containing numerous experiments 

 confirming those which had been previously made, or supply- 

 ing the deficiency which existed as to the atomic weights of va- 

 riorts bodies, both simple and compound. 



After a preface and advertisement, we are presented with an 

 historical introduction of the atomic theory, occupying twenty- 

 eight pages : in this sketch we think tne author has fairly 

 allotted to each philosopher the portion of merit due to him ; 

 there are, however, some statements which call for obser- 

 vation ; and especially with respect to the substance by which 

 the atomic unit is preferably represented — whether by hydrogen 

 or oxygen. Dr. Thomson remarks, p. 14, " Mr. Dalton made 

 choice of the atom of hydrogen for his unity ; and in this he has 

 been followed by Dr. Henry, of Manchester, and by one or two 

 chemical gentlemen in London. But this method has been 

 rejected by almost all the British chemists, and by all the che- 

 mists, without exception, in Europe and America." Has Dr. 

 Thomson forgotten, that Sir H. Davy, in his Elements of Chemi* 

 cal Philosophy, has adopted hydrogen as unity? We shall 

 not follow the author in all his arguments for preferring oxygen ; 

 the strongest of these, and in our opinion indeed the only 

 one w^hich possesses any weight, and that but little, is that 

 " we see at once by a glance of the eye the number of atoms of 

 oxygen which enter into combination with the various bodies.*' 

 This fact the Doctor has illustrated by reference to that case 

 which of all others best proves it, viz. the six oxides of manga- 

 nese, for no other body forms so many oxides ; but this facility is, 

 we think, more than counterbalanced by the difficulty of seeing at 

 a glance whethertheproposed atomic weight of a body is probably 

 the true one, by determinining whether it is a multiple of the 

 atom of hydrogen by a whole number ; thus oxygen being unity, 

 fuming sulphuric acid, is represented by 11*125: now it requires 

 an. operation to discover that this is equivalent to 0*125 x 89, 

 and 89 is, in our opinion, a much more convenient number, and 

 more likely to be retained in the memory than 11'125, unless by 



