of Chemical Operations. 427 



might happen in this case also that two different hypotheses, 

 both including the whole of the known phenomena, should 

 lead to different deductions, and present different consequences 

 which should guide the operator into two distinct paths. 

 When things occur thus, it is useful to accept the two hypo- 

 theses at once, and since no objective reality is attributed 

 to them until experience has decided (when experience can 

 decide), both are undeniably useful. Sir B. C. Brodie's 

 system, by showing the possible decomposition of the whole of 

 one class of our elements, and by indicating one of the pro- 

 bable cases in which these elements are decomposed (the cases 

 of binoxide and tetroxide of nitrogen), renders a real rervice 

 to chemical science, and deserves to be known and studied. 

 It will deserve this still more, if it be found that in working it 

 out and perfecting it its defective sides are caused to disappear 

 and its completion effected. It will help to place Chemistry 

 on a solid foundation ; and such an attempt has a right to the 

 sympathetic attention of the whole scientific world. 



Postscriptnm. Since these lines were written some curious 

 observations have allowed scientific men to consider as pos- 

 sible, as even probable, the production of free hydrogen by 

 the action of an extremely elevated temperature on the greater 

 number of our elementary bodies. It is useless to demonstrate 

 — it demonstrates itself — the value which this discovery, if it 

 is confirmed, would give to Sir B. C. Brodie's hypothesis. 



Note on an Objection made by M. Naquet in his preceding 

 "Observations:' By Sir B. C. Brodie, F.R.S* 



M. Naquet has had the kindness to forward to me the proofs 

 of his " Considerations " on my Memoirs. It is not my wish 

 to comment here on his remarks ; but there is one point in 

 reference to which the remarks of M. Naquet are founded on 

 a pure misapprehension of the state of the case. This point 

 is of fundamental importance; and I will give a few words of 

 explanation in regard to it. Indeed, if the difficulties which 

 he has created really existed, the atomic method would have 

 in some respects a great advantage over the method of this 

 Calculus. I will explain the matter as briefly as possible. 

 The objection of M. Naquet is this. We may, according to 

 the atomic method, operating by way of substitution of atom 

 for atom, foresee in certain cases the number of practicable 

 substitutions. Thus, marsh- gas (CH 4 ) containing four atoms 

 of hydrogen, we may substitute in it chlorine for hydrogen 



* From the Moniteur Scientifique of Dr. Quesneville, April 1879. 



