948 MR A. CRICHTON MITCHELL ON THE 



material gains enormously in toughness and tensile strength, while the hardness which is 

 so marked in the lower percentage is lessened. The same holds with higher proportions 

 up to 25 per cent. Thus, taking into consideration as well the other properties to be 

 immediately mentioned, we find that while iron and manganese alloys containing upwards 

 of 7 "5 per cent, of the latter present features more akin to those of steel, others with 

 higher proportions, exceeding 7 '5 per cent., have the entirely different characteristics of 

 what is practically a new substance. As already mentioned, it is to that particular alio} 7 , 

 containing from 10 to 15 per cent, of manganese, that the name " manganese- 

 steel " has been given. 



The chemical composition of manganese-steel varies, but the following may be taken 

 as an average : — 



Carbon, 



Silicon, 



Sulphur, 



Phosphorus, 



Manganese, 



- 85 per cent. 

 0-23 

 0-08 

 0-09 

 13-75 



Its density is 7 '8 3 ; practically the same as wrought iron. Its hardness is of a some- 

 what peculiar nature. Thus, while to drill a hole in manganese-steel takes 15 or 20 times 

 longer than in ordinary steel, and while it is hard enough to scratch any steel but the 

 hardest-tempered, yet it may easily be indented by a blow from a hand-hammer. It is 

 also strange that, being so difficult to drill, or to cut with a planing-tool, when subjected 

 to a compression-load of 100 tons, cylinders of manganese-steel, 1 inch long, 0'75 inch 

 diameter, were shortened 0'25 inch; while chilled iron cylinders of exactly the same 

 dimensions, and under the same conditions, were scarcely altered. The tensile strength 

 varies from 50 to 65 tons per square inch, according to the mode of treatment. Hard- 

 drawn manganese-steel wire will, however, stand upwards of 110 tons per square inch. 

 The tensile strength is greatly increased by the process known as "water-toughening"; 

 i.e., raising the material to yellow heat, and immediately plunging it into cold water. 

 The elongation under stress is much greater in this alloy than in steel of the ordinary 

 kinds, being in some cases as much as four times. Steel with a tensile strength of 60 

 tons per square inch seldom gives more than 10 per cent, elongation ; while a similar 

 bar of manganese-steel will give 50 per cent, elongation. 



When manganese-steel is subjected to the usual process employed in tempering steel, 

 it behaves in an unusual manner. " Water-toughening " makes it softer ; heating it, 

 and allowing it to cool in air, hardens it ; sudden cooling also increases its ductility. 

 These effects are the reverse of what takes place in ordinary steel. 



One of the most peculiar features about this alloy is that it is almost non-magnetic ; 

 a fact first pointed out by Mr Bottomley * and Dr HoPKiNSON.t Since then, Professor 

 EwnroJ has fully investigated its magnetic properties. He finds that its magnetic suscep- 



* B.A. Report, 1885, p. 903. t Phil. Trans., 1885, Part II. t B.A. Report, 1887, p. 587. 



