70 ANNUAL OF SCIENTIFIC DISCOVERY. 



If the compression of the particles of the central steel predomi- 

 nates over the displacement of the particles of the outer steel, the 

 piece of steel under operation will then be smatler in dimensions. 

 In other words, if the expansion of the outer steel amounts to 

 more than the compression of the central steel, the piece of steel 

 will increase in bulk ; if the compression of the central steel 

 amounts to more than the expansion of the outer steel, the piece 

 of steel will then decrease in bulk. The expansion of the steel is 

 greatest when it is heated to a high degree of heat before im- 

 mersion. This effect is owing to the particles being displaced at 

 a still greater distance from each other, and which may, in some 

 measure, account for the brittleness of steel when overheated. 

 This expansion is, in some measure, reduced by tempering; and 

 this effect is caused by the hardness being reduced, and allowing 

 the particles to partly rearrange themselves in their natural po- 

 sitions. 



The expansion of steel is prevented in some measure by an- 

 nealing the steel about three times previous to its being finished, 

 turned, or planed ; for instance, after the first skin is cut from the 

 steel it should be annealed again, after which another cut must be 

 taken from it and again annealed, and so the third time. This 

 may appear to some like frittering away time ; but in many in- 

 stances the time will be more than saved in lapping or grinding 

 to their proper sizes after the articles are hardened, especially 

 when it becomes necessary. to lap or grind them by hand labor; 

 for hardened steel works with great difficulty. Therefore in some 

 instances it becomes a matter of importance in hardening to keep 

 the article as near as possible to its original size. Articles made 

 of steel, which have been well forged, will always keep truer and 

 keep their original sizes better in hardening, and be less liable to 

 break in hardening, than articles which are made of the steel in 

 the state it leaves the manufacturer. Ede on Steel. 



IMPROVED STEEL-HEADED RAIL. 



It is generally conceded by railway engineers that Bessemer 

 steel rails will wear about 16 times as long as common iron rails. 

 If such be the fact it is a matter of the utmost importance that 

 railway companies renew thoir roads with steel rails or steel- 

 headed rails as soon as those already in their tracks are worn out. 

 Some of the first engineers in the country have expressed them- 

 selves in favor of steel-headed rails, provided the steel head could 

 be welded perfectly to the iron, as in this country the weather is 

 so intensely cold in winter that rails made entirely of steel are 

 very liable to break. It is well known to all that until quite 

 recently steel-headed rails have proved a failure, for the reason 

 that it is such a difficult matter to heat a rail pile composed of iron 

 and steel according to the usual mode of piling; as the iron re- 

 quires about double the heat to bring it to a welding state that 

 steel does : consequently either the iron is not heated sufficiently 

 to weld, or the steel is overheated, which destroys its properties 

 altogether. In either case the rail is unfit for use. As a general 



