On the Oxidation of the Constituents of Ammonia. 4i^7 



apprehend, would be only verbal, for it amounts to saying that it 

 contains a real as well as a nominal definition. It is an objec- 

 tion which may be raised in regard to any adequate mathemati- 

 cal definition whatever. " We might/^ says Dr. Whewell, " begin 

 by defining a right angle to be the angle made by a line which 

 stands evenly between the two portions of another line ; and we 

 might add an axiom, that all right angles are equal. Instead of 

 this, we define a right angle to be that which a line makes with 

 another when the two angles on the two sides of it are equal. 

 But in all these cases we express our conceptions of a necessary 

 relation of lines ; and whether this be done in the form of defi- 

 nitions or axioms, is a matter of no importance.^^ 



That Euclid^s 12th axiom is the same in kind as his definition 

 of a circle, right angles, &c., has been universally acknowledged. 

 In the celebrated controversy on the grounds of mathematical 

 reasoning, D'Alembert calls it a definition, and, except in the 

 mere question of nomenclature, which cannot afi'ect the point I 

 have attempted to establish, his opponents agree with him. It 

 appears to be of some importance that we should bear this fact 

 in mind when discussing the theory of parallels. 



The Cloisters, Inner Temple, 

 fy ,^ij; November 8, 1856. 



LIX. On the Oxidation of the Constituents of Ammonia hy Porous 

 Media, with some Remarks on Nitrification, By Prof. Schon- 

 BEiN of Basle^. 



My dear Faraday, 

 .... O INCE I last wrote to you I have actively continued my 



^^ researches on the phsenomena of contact, and obtained 

 some results which are curious enough. You know perhaps, 

 that, according to my former experiments, ozonized oxygen at the 

 common temperature oxidizes both the elements of ammonia, 

 forming with that compound nitrate of ammonia ; whilst, as you 

 are well aware, common oxygen under the same circumstances 

 does not at all afi'ect either gaseous or aqueous ammonia. The 

 same oxygen, however, on being piit in contact with certain mat- 

 ters, acquires the power of engendering, with ammonia, nitrous 

 acid, i. e. nitrite of ammonia. Platinum and copper are such 

 matters. Moisten the former metal (in the state called platinum 

 black) with a strong solution of ammonia, leave these substances 

 exposed for a short time to the action either of common oxygen 

 or atmospheric air, then treat the metallic powder with some di- 

 stilled water, and you will easily detect in the liquid the pre- 

 * Communicated by Professor Faraday, 



Phil. Mag. S. 4» Vol. 1^. No. 81. Dec. 1856. 2 H 



