THE CORROSION OF IRON AND OTHER METALS 329 



The Corrosion of Copper and of Copper Alloys 1 



The general lack of understanding of the conditions which 

 determine the corrosion of copper and its alloys would seem 

 to be even greater than is the case with iron. The chemical 

 text-books give no sound information on the subject ; even the 

 fact that copper is dissolved by a hot solution of hydrogen 

 chloride is very commonly overlooked, as Tilden pointed out 

 to little purpose years ago {Journal of the Society of Chemical 

 Industry, 1886, p. 84). Theoretically copper should not be 

 soluble in chlorhydric acid if the interaction involve merely the 

 formation of cupric chloride and hydrogen, as such a change 

 would be attended with an absorption of energy. Thus, taking 

 Julius Thomsen's figures : 



CuO = 37,160 gram-deg. C. heat-units 



CuO . 2HCI Aq = 15,270 „ „ 



52,43° 



since the heat of formation of water is included in this value, 

 the heat of dissolution of copper in chlorhydric acid will be — 



52,430 - 68,360 = -15,930 units. 



A like argument is applicable to nitric and sulphuric acids. Veley 

 moreover has shown, by a most exhaustive series of experi- 

 ments {Roy. Soc. Phil. Trans. 1891 A. 182, 279), that nitric acid 

 free from nitrous compounds will not dissolve copper ; and it is 

 well known that copper will not dissolve in dilute solutions of 

 sulphuric acid or in organic acids, except in presence of oxygen. 

 The direct dissolution of copper by chlorhydric acid is 

 probably to be accounted for as the consequence of the for- 

 mation of cuprous chloride. The dissolution of copper by 

 ordinary nitric acid doubtless takes place in a circuit which 

 includes not only the acid but also nitrogen dioxide or some 

 other nitrous compound which acts as the depolariser, throwing 

 energy into the circuit. Hot sulphuric acid is a solvent of 

 copper probably not because the acid acts when hot though 



1 "A Report to the Corrosion Committee of the Institute of Metals." By Guy 

 D. Bengough, M.A., The Journal of the Institute of Metals, vol. v. No. I, 191 1. — 

 On the Failure of a Brazed Joint. By Prof. Henry Louis. — The Corrosion of 

 Brass with Special Reference to Condenser Tubes. By Paul T. Briihl, M.Sc, Meet- 

 ing of Institute of Metals, Sept 191 1 .— The Hard and Soft States in Metals. The 

 Second May Lecture of the Institute of Metals, May 12, 191 1, by G. T. Beilby, 

 F.R.S. 



