344 'Analysis of Scientific Books. 



In adverting- to this subject, the Reviewer certainly did mean 

 to arraign the Doctor's accuracy and candour for setting up 

 pretensions to a discovery which was probably never made, and 

 which, at all events, from its date could not affect the prior 

 claim of the English philosopher. 



Dr. Thomson confesses his blunder, pointed out by the Re- 

 viewer, in respect to fluorine ; but softens it into an arithmetical 

 error, sinking the long train of theoretical nonsense which he had 

 tacked to its tail. The atomic number 1.25, which he now 

 gives for fluoric acid, is very nearly that, deducible from an 

 experiment long ago made by Sir H. Davy, on fluate of potash. 

 " Twenty-two grains of fused sub-carbonate of potash, decom- 

 posed by diluted liquid fluoric acid, in an experiment made 

 with great care, was found to afibrd 18.15 grains of dry fluate 

 of potash*. But 22 : 8.75:: 18.15 : 7.22; from which sub- 

 tracting the atomic weight of potash 6, we have 1.22, to repre- 

 sent an atom of fluoric acid. 



In Dr. Thomson's Answer, we find one instance of complai- 

 sance, which we shall try to repay. " I shall gratify," says he, 

 " this laudable curiosity of the Reviewer. 1 ascertained the 

 volume of oxygen gas in the olefiant gas, by means of nitrous 

 gas, employing Dalton's formula for the purpose t." We are 

 surprised that so doughty a disputant, should betray the secret 

 of his errors in so silly a way ; for Dr. Thomson, in the 6th 

 edition of his System, condemns Mr. Dalton's formula, which, 

 indeed, had been shewn long ago by M. Gay-Lussac, to be 

 good for nothing. Describing Mr. Dalton's formula, Thom- 

 son says, " To 100 measures of air, add about 36 of nitrous 

 gas; note the diminution of bulk, and multiply it by ^^ ; the 

 product gives the bulk of oxygen in the air examined. / have 

 made many experiments on this subject ; but have ^ot obtained 

 results agreeing with each other. Sometimes the multiplier is 

 ^ = 0.3684 ; while sometimes it is as high as f J- = 0.42 J." It 

 was the French philosopher who first cleared up by his doc- 

 trine of volumes (so strangely resisted by Mr. Dalton,) all these 

 perplexities ; thus reducing the analysis of air, or gaseous mix- 

 tures containing oxygen, to great simplicity and precision. 

 Dr. Thomson will find a full account of this important part of 

 practical chemistry, in the Dictionary of Chemistry, Article, 

 Eudiometer. 



In our Review, p. 145, his ignorance of the mode of working 

 simple equations in algebra is exposed, though he is perpetually 

 involving the plainest cases of arithmetic in a mist of algebraic 

 symbols, as pedants .nake unlucky quotations from languages 

 they do not understand. The merest tyro in calculation, would 

 have been chastised at school for committing the Doctor's 



■»• rhil. Trans. 1814. t Answer, p 267. 



J Sy>tein, 6lh Edit. III. p. 168. 



