METALLURGY. 



533 



structure of various kinds of cast-iron appears 

 to be chiefly modified by the presence of crys- 

 talline plates of graphite, over which is depos- 

 ited what is probably free iron, while the inter- 

 spaces are filled with what are probably two 

 distinct compounds of iron and carbon. In 

 other cases, the structure is mainly dependent 

 on the crystallization of the iron itself, the 

 graphite being thrown off toward the close of 

 the process. In white refined iron the princi- 

 pal constituent is probably an intensely hard 

 refined white iron with much carbon, and one 

 or more of the other compounds of iron and 

 carbon. Hammered bloom consists of an ir- 

 regular mixture of crystals of iron and portions 

 of slag. When rolled into a bar those portions 

 of slag not squeezed out are thrown out into 

 long threads. The crystals seen in the bar are 

 not the original crystals of the bloom, but fresh 

 crystals formed on the cooling of the bar. The 

 fiber seen on fracturing specimens of wrought- 

 iron is mainly due to the elongation that occurs 

 during the fracture, and is not a characteristic 

 of the unaltered iron. The most characteristic 

 feature of the change of structure produced by 

 the cementing process is the development of a 

 network of flat crystals of an intensely hard 

 compound of iron and carbon, which is scarcely 

 acted upon by dilute acid. The structure of 

 Bessemer steel ingots is materially different 

 from that of the varieties of steel containing 

 more carbon, and, though of coarser grain, 

 closely approaches the structure of some vari- 

 eties of Swedish iron. This structure, upon 

 hammering, is greatly altered, and becomes of 

 finer grain and more uniform. 



Mr. J. 0. Bayles, of New York, after review- 

 ing before the American Institute of Mining 

 Engineers the researches of Mr. A. Martens, of 

 Berlin, and Mr. Sorby, on this subject, and 

 giving an account of his own method of pre- 

 paring the objects for examination, expressed 

 the belief that the method opens a vast field 

 of knowledge not yet reached by either chemi- 

 cal analysis or physical test. There are many 

 conditions the result of changes produced by 

 mechanical treatment to which chemical analy- 

 sis gives no clew, and which are detected but 

 not explained by the tests of the physical labo- 

 ratory. 



DETERIORATION OF TIN. At a late meeting 

 of the American Institute of Mining Engineers 

 Professor R. H. Richards, of Boston, exhibited a 

 pig of block-tin which had appeared to be of a 

 perfectly good quality, but was found after the 

 lapse of a few months to have become brittle, 

 and to have undergone a change in its molecular 

 condition that involved about half of the mass. 

 The change made itself apparent by enlarge- 

 ment in spots which took on a darker color 

 and revealed a crystalline structure like that 

 of stilbite. It was believed to be due to the 

 presence in the tin of a small percentage of 

 mercury with which the metal was originally 

 treated, left after an imperfect heating; and 

 the analysis of a part of the pig showed that 



about 2 '62 per cent of mercury was actually 

 present. The fact of this deterioration taking 

 place is not new. Dr. T. Sterry Hunt called 

 attention to the fact that it had previously 

 been ascertained that block-tin, under certain 

 conditions, would undergo the changes de- 

 scribed ; and he cited an instance of a piece of 

 the metal which, supposed to be in a state of 

 purity, afterward became so crystalline that it 

 was almost ready to fall to pieces. 



IMPROVEMENTS IN ELECTRO -PLATING. Some 

 further improvements in the electro-deposition 

 of brass, bronze, and other metals have been 

 patented by Mr. W. H. Walenn, of London. 

 The first object of the inventor was to produce 

 a coating that should be adherent and in a soft 

 condition. For this a solution is used which 

 is composed of thirty-two ounces avoirdupois 

 of cyanide of potassium (70 per cent real cya- 

 nide) and one ounce of neutral {artrate of am- 

 monium per gallon of liquid, which is charged 

 with copper by an electrolytic process, and is 

 made complete by the addition of cupric am- 

 monide. The solution is used at a boiling-point, 

 or near to it, when the coating of copper is soft- 

 ened, and the rate of deposition is very materi- 

 ally increased by the heat. The quality of the 

 work done by this process is illustrated by the 

 fact that thin sheet-iron plates treated by it have 

 been given a coating so adherent that repousse 

 work could be executed upon them without 

 interfering with the continuity of metal and 

 without exposing the coated metal underneath. 

 If a plate were hammered to destruction, the 

 copper coating would be simply extended over 

 the iron where it was cracked or broken. Mr. 

 Walenn's invention also includes methods of 

 preventing the too great evaporation of the 

 solution while it is heated during deposition, 

 for working the electro-depositing solutions in 

 a closed vessel under a known pressure. 



PROTECTION OF IRON AND STEEL SURFACES 

 FROM RUST. The Bower-Barff process for 

 preserving iron and steel from rust is based 

 on the fact that a film of magnetic oxide on 

 the surface of a mass of either metal will pro- 

 tect the whole from further oxidation or cor- 

 rosion. The resisting power of Russia sheet- 

 iron has been found to be due to this cause. 

 To Professor Barff is due the credit of being 

 the first deliberately to undertake to coat iron 

 and steel with magnetic oxide produced design- 

 edly for the purpose of protecting their sur- 

 faces from rust. To effect this, he subjected 

 the metal to the action of superheated steam. 

 The Bower process is based upon the use of 

 combustible gases and air, or free oxygen. The 

 gases are burned in a fuel gas-producer, which 

 is similar in principle to the Siemens regener- 

 ator, with a slight excess of air over that re- 

 quired for perfect combustion, while the iron 

 articles to be heated and oxidized by the prod- 

 ucts of the combustion are exposed to them in 

 a suitable brick chamber. When the quantity 

 of free oxygen mixed with the products of 

 combustion is rightly adjusted, the iron articles 



