Mr Dalton's System of Chemical Philosophy. 347 



The last method by nitrous gas, has indeed been proposed before, and la- 

 bour bestowed on it both by others and myself, but without reducing the 

 results to any certainty, till lately ; the principal cause of this want of 

 success has arisen from misunderstanding the nature and constitution of 

 nitric acid." (Page 4.) " It sometimes? happens that the nitrous gas is 

 partly or wholly retained by the residue of nitric acid ; but in this case the 

 oxymuriate of lime may be applied to convert the nitrous gas into nitric 

 acid." (Page 5.) 



Accordingly this method of ascertaining the proportion of oxygen which 

 enters into combination with a metal is the one adopted by Mr Dalton. 

 The metho{l, we should apprehend, is one not likely to be approved by 

 practical chemists ; for though assuredly it must be possible in some in- 

 stances to ascertain the combining oxygen by this method ; yet there is 

 hardly an instance where other methods equally easy and more susceptible 

 of accuracy could not be adopted. Besides, the method rests on a some- 

 what remote deduction from an assumption that the sole product is a ni- 

 trate. Now we know that ammonia results in some cases from the action 

 of nitric acid ; and its production ought perhaps to be suspected in other 

 eases where it has not yet been ascertained. Accordingly we find Mr Dal- 

 ton stating (page 31) that his experiments on the nitric oxide evolved by 

 iron and nitric acid did not afford " satisfactory" data for deducing the 

 oxygen which combines with iron. Part of the nitric oxide was retained 

 by the iron solution ; and when in order to convert this into nitric acid 

 he added a solution of bleaching powder, a pungent gas was evolved, which 

 he supposes to be a compound containing more oxygen than nitric acid. 

 We have no doubt that this " pungent gas" is the same again mentioned 

 by Mr Dalton (Appendix, page 336,) as an accompaniment to the azote 

 evolved when an ammoniacal salt is mixed with a solution of bleaching 

 powder—" exciting sneezing, and inducing catarrh." The offensive va- 

 pour which produces these effects is chloride of azote derived probably in 

 the case of the iron solution from the action of dissolved bleaching pow- 

 der or nitrate of ammonia. Since we are upon the subject, we may ob- 

 serve that it is by no means easy to obtain azote quite free from all smell 

 of chloride of azote, by decomposing ammonia by means of chlorine ; and 

 if we should attempt to free the azote of chloride by washing, we run 

 equal risk of contaminating the azote with other gases separated from the 

 Vater. Messrs Berzelius and Dulong {Annates de Chimie et de Physiqucy 

 vol. XV. page 390) procured the azote of which they took the specific gravity 

 by decomposing ammonia by chlorine ; and the reason that they obtained 

 the specific gravity .976 which Messrs Biot and Arago before then got 

 .968 probably was that their azote retained a trace of chloride of azote. 

 At least we are certain that either their specific gravity of oxygen or of 

 azote must be too much or that of air too little ; for, taking tlie air to con- 

 sist of .21 of oxygen by bulk and .79 of azote, 1. of air by bulk, yields by 

 computation a specific gravity of 1.0026 instead of 1. Admitting the spe- 

 cific gravity of oxygen to be as they state it, we would have to reduce that 

 of azote to .9727, in order to make that of air 1. Besides oxygen and azote, 

 Messrs Berzelius and Dulong took the specific gravity of hydrogen and of 



