40 ANNUAL OF SCIENTIFIC DISCOVERY. 



LARGE IRON FORGING S. 



Mr. R. Mallet has read to the London Institution of Civil Engineers a 

 paper "On the Coefficients of Elasticity and of Rupture in "Wrought Iron, in 

 relation to the volume of the metallic mass, its metallurgic treatment, and 

 the axial direction of its constituent crystals." 



Iron was formerly entirely worked under tilt-hammers; the process of 

 rolling was then introduced; and now, in consequence of modern engineer- 

 ing requirements, masses of iron, ot considerable magnitude, were produced 

 by faggoting- together, under heavy forge-hammers, from large numbers 

 either of bars or slabs grouped together. The masses were not, however, 

 found to possess ultimate strength in proportion to the number of bars of 

 which they were composed; in fact, it appeared that the strength of the 

 mass became less in some proportion as the bulk became greater. This was 

 admitted as a fact, but no one had hitherto attempted to show experimen- 

 tally what function of the magnitude was the strength of a given kind of 

 iron, manufactured in a given manner; or how the same forged mass, when 

 very large, differed in strength in different directions, with reference to its 

 form; or how the mechanical part of the process of manufacture of the 

 same iron affected its actual strength, either as a rolled bar or as a forged 

 mass. 



Addressing himself to this investigation, the author dealt generally with 

 three points of the inquiry, viz. : 



1. What difference did the same large bars of unwrought iron afford to 

 forces of tension and of compression, when prepared by rolling, or by ham- 

 mering under the steam-hammer? 



2. How much weaker, per unit of section, was the iron of very massive 

 hammer forgings, than the original iron bars of which the mass was com- 

 posed? 



3. What was the average, or safe, measure of strength, per unit of sec- 

 tion, of the iron composing such very massive forgings, as compared with 

 the acknowledged mean strength of good British bar iron ? 



We have not space for the illustrative details, but the conclusions deduced 

 were, that practically the iron of very heavy shafts, forged guns, huge 

 cranks, and other similar masses, might be expected to become permanently 

 set and crippled at a trifle above seven tons per square inch, and to give 

 way by fracture at about fifteen tons per square inch by tension, and to 

 completely lose form at pressures of from fifteen to eighteen tons per square 

 inch. Therefore it followed that, allowing a deduction of one-half, as sanc- 

 tioned by practice, from the elastic limits of tension and of pressure, for the 

 margin of safety, the iron of such forged masses should not be trusted for 

 impulsive strains exceeding about one and three-fourths tons per square 

 inch of tension, and about four and a half tons per square inch of pressure, 

 or for passive tensile strains of three and a half tons per square inch, or for 

 passive pressure beyond nine tons per square inch., 



THIN CAST IRON. 



At a recent meeting of the Manchester Philosophical Society, Mr. Fair- 

 barn, the President, exhibited two large pans of cast iron, procured from 

 China, where they are used for boiling rice. The metal, which is at the 

 strongest part only one-tenth of an inch in thickness possessed considerable 



