COATING OF IRON OR STEEL — FORBES. 29 



The treatment thus extended results in a much darker color, 

 approaching very nearly to a black, and where it is intended to 

 produce this kind of" a finish, the surface need not be carefully 

 polished beforehand, a smooth and even surface, (with, however, 

 a full exposure of the clear metal), being all that is needed, as 

 the surface after treatment presents a fine granular character, 

 quite pleasing to tlie eye, but without polish, even though it 

 may have been polished previous to treatment. 



It is, however, necessary in order to oljtain good results, that 

 the suface be made clean, so that free action of the oxidizing- 

 agent may not be interfered with. 



The extent of the treatment, and consequent depth of the 

 scale formed, must of course be modified to suit the purposes for 

 which the articles treated are intended to be used. 



This kind of coating, as a preventive from further oxida- 

 tion, has enofagfed the attention of scientific men, and several 

 methods have been proposed for producing it. 



About fourteen years ago, Prof. Barfi", of some part of England, 

 devised a method of submitting the articles to be treated to the 

 action of steam, the articles having been raised to a suitable de- 

 gree of heat in a muffle, the steam was then admitted, and 

 becoming decomposed, the oxygen combined with the iron, and 

 the hydrogen was enabled to escape by a suitable exit pipe. 



At first this method was not quite successful, because although 

 the desired oxidation was obtained, j^et it was not satisfactorj^ 

 because it did not stick to the iron, but was formed in minute 

 scales that were easily detached. This was afterwards remedied 

 by using superheated steam and quite satisfactory results were 

 then obtained, and tlie articles so treated present a very nice ap- 

 pearance. The method, however, requires a properly erected 

 apparatus, at a considerable outlay, for its accomplishment. A 

 short time after Prof. Barfi"s method was introduced, another 

 method of accomplishing the result was invented by a Mr. Bower, 

 of England. Mr. Bower's method consisted in subjecting the 

 suitably heated articles, they being also enclosed, to the action of 

 hot air — the supply of air being renewed from time to time as it 

 became deoxidized, and fresh supplies introduced into the cham- 



