164 Intelligence and Miscellaneous Articles. 



" To account for the production of heat and light during com- 

 bustion, Lavoisier had recourse to Black's theory of latent heat. 

 Heat is always evolved when a substance, without change of form, 

 passes from a rarer into a denser state, and also when a gas be- 

 comes liquid or solid, or a liquid solidifies, because a quantity of heat 

 previously combined or latent within it is then set free. Now this 

 is precisely what happens in many instances of combustion. Thus 

 water is formed by the burning of hydrogen, in which case two 

 gases give rise to a liquid ; and in forming phosphoric acid with 

 phosphorus, or in oxidizing metals, oxygen is condensed into a solid. 

 When the product of the combustion is gaseous, as in the burning 

 of charcoal, the evolution of heat is ascribed to the circumstance 

 that the oxidized body contains a smaller quantity of combined heat, 

 or has a smaller specific heat than the substance by which it is 

 produced.''' 



This passage, combined with that which immediately succeeds it, 

 and which I abstain from quoting merely because of its length, 

 enunciates very distinctly the views which I have ascribed to La- 

 voisier in relation to the origin of heat and light which accompany 

 combustion. If they are mistaken views, I have, at all events, the 

 consolation of having fallen into error in good company. 



I may, in conclusion, observe that I fear I have suffered much in 

 the estimation of the reviewer by continuing to employ the dua- 

 listic * methods of explanation, and the atomic weights long in use 

 among chemists, instead of those of the unitary system, of which, I 

 make no doubt, he is a zealous advocate. In my introductory chapter 

 I have explained my motives for adhering, at least for the present, 

 to the equivalents and the language of Berzelius and Davy, and I 

 regret that before entering on the details of the work, he did not, as 

 it were, lay the axe to the root, and point out the errors I may have 

 committed in such fundamental discussion. If convicted of any 

 inaccuracies, either of statement or inference, in relation to the 

 system of the illustrious Gerhardt, I trust I have given sufficient 

 proof that I would be prepared to admit them, and, as far as pos- 

 sible, atone for them. 



James Apjohn, M.D., F.R.S., M.R.I.A., 

 Professor of Chemistry in the University of Dublin. 



Out of deference to Professor Apjohn's wishes, we have adopted 

 the somewhat unusual course of publishing his reply to the criticisms 

 on his work entitled ' A Manual of the Metalloids/ which appeared 

 in the last Number of this Journal. Upon this reply, the reviewer 

 claims the right of adding the few following remarks : — 



Professor Apjohn's work is intended for the use of junior students 

 in chemistry, and comes before them, not only with the prestige 

 conferred upon it by the distinguished position of its author, but 

 with the additional advantage of being published as one of a series 



* This phrase is at present sometimes used as one of reproach by gen- 

 tlemen who have studied chemistry in a German school, and who are quite 

 satisfied with the fictions of the unitary system. 



