Thomson's System of' Chemislry. 151 



and mercury, are all mere affairs of the printer, except short 

 notices about their seleniurets. We were not a little surprised 

 to find, that he took no notice of Mr. Donovan's new deter- 

 mination of the proportion of oxygen in the mercurial oxides, 

 after the numerous panegyrics which he has pronounced on his 

 paper. " He finds," says the Doctor, " the composition of the 

 two oxides of mercury, as follows : 



Protoxide 100 mercury, + 4.12 oxygen. 



Peroxide 100 . + 7.82. 



Mr. Donovan informs us that, though he repeated his ex- 

 periments several times, the results were precisely as above 

 stated. They do not accurately correspond with the atomic 

 theory, and therefore cannot be quite correct ; but if we take 

 the mean of the two, we obtain the composition of the two 

 oxides of mercury as follows 



Merc. Oxyg. 



Protoxide 100 -f 3.98 

 Peroxide 100 + 7.96 

 numbers which differ very little from those determined by 

 former experiments*." 



Here are committed two distinct and independent errors, in 

 two different compounds, one in excess, the other in defect, 

 and by taking the mean, truth is to be obtained ! Has the 

 Doctor any notion of logic ? 



The articles gold, platinum, palladium, rhodium, iridium, 

 antimony, chromium, molybdenum, tungsten, columbium, and 

 titanium (with which the first volume concludes) are copied ver- 

 batim from the old edition. We perceive merely a new notice of 

 the ignition produced by exposing platinum, in contact with tin 

 or antimony, to a moderate heat. 



Having devoted so much attention to his first volume, which 

 in fact contains the substance of his system, we shall take but a 

 cursory view of the remainder. The Doctor commences his 

 second volume with the following paragraph : " In the present 

 state of the science of Chemistry, I have thought it belter to 

 describe several of the compound substances, while treating in 

 the last book, of the simple bodies, by the union of which they 

 are constituted, than to place all the compounds under distinct 

 heads. A contrary plan has been followed by some modern 

 writers, but I think the result has been such, as ought to deter 

 others from imitating their example. The unity of the subject 

 has been destroyed, and the facts have been exhibited in so un- 

 connected a manner, as must considerably retard the progress 

 of the student, while it fatigues and disgusts those who are 

 already acquainted, with the subject." Is Dr. Thomson aware 

 what a graphical picture he has been drawing of his own work ? 



* Annrdt of I'lulnsnphy, p. 17, 18. 1820. 



