MECHANICS AND USEFUL ARTS. 29 



finely granular, and ^Tstalline ; that of 50.3 iron yields a some- 

 what spongy button with metallic globules; its fracture i\m-\y 

 granular, bright, and grayish white. The alloy of 25.3 per cent, 

 iron is obtained as an imperfecth^ fused spongy mass, of less co- 

 herence than the former, a yellowish-gray white color and some- 

 what dull lustre. The alloy containing 17 per cent, of chromium 

 is described by Berthier as almost silver white, fibrous in structure, 

 and with difficulty attacked by acids. That containing CO per 

 cent, of chromium scratches glass better than tungsten steel, and 

 almost as deeply as the diamond. 



With regard to steel, Berthier found that 1 or 2 per cent, 

 of chromium when added to molten metal communicates hardness 

 and the property of taking a very beautiful damask, without 

 diminishing its malleability. Faraday and Stodart examined 

 steel containing nearly 3 per cent, of chromium, and found it 

 to be as malleable as pure iron and giving a very fine damask. 

 The damask was removed by polishing, and restored by heat 

 without the use of any acid. 



The use of chromnte of iron, or chrome ore, for hardening iron, 

 has lon^ been known ; but it is only recently that attention has 

 been paid to its practical use for this purpose, the chrome ores hav- 

 ing been almost exclusively used for the manufacture of bi-chro- 

 mate of potash for coloring purposes. Late experiments have 

 demonstrated its superiority as an alloy for hardening steel, and 

 for the manufacture of burglar-proof safes. The chrome-iron 

 safes are cast, and are impervious to acids or drills, and the ma- 

 terial is by far the hardest metal ever discovered. 



These allo3's may also be made with chrome-iron ores, by 

 using a flux to retain the silica and alumina which may be present 

 in the ores. A good flux for this purpose is a mixture of 100 

 parts glass (free from lead), and 40 of glass of borax, to 100 of 

 ore. 



The supply of chrome-iron ore in this country is quite exten- 

 sive; and it is found of superior quality at the Bare Hill, about 6 

 miles from Baltimore, in Harford County, and in other parts of 

 Baltimore County, and many parts of Chester, Delaware, and 

 other counties of Pennsylvania. — Scientijic American. 



CARBON IN IRON. 



It is well known that there are two states in which carbon exists 

 in solid iron, — a state of chemical combination with the iron, and 

 a state of merely mechanical dift'usion througii its mass. It is 

 also known that the carbon existing in iron in the last-mentioned 

 state is always in the form of graphite. Dr. Phipson has recently 

 announced to the Academy of Sciences that he has discovered 

 that siliciura also may exist in cast iron, either in a state of com- 

 bination, or in a state of diffusion racreh% and that, like carbon, 

 when merely diffused through the iron, and not in comI)ination 

 therewith, it is always in the graphite form. He adds, what, if 

 true, is of great practical importance, that, upon the condition of 

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