408 THE SCIENTIFIC PAPERS OF 



In the discussion of the Paper 



"ON SOME PHYSICAL CHANGES OCCURRING IN 

 IRON AND STEEL AT HIGH TEMPERATURES," 



By Mr. T. WRIGHTSON, 



DE. SIEMENS * said that owing to a bad cold he should have 

 difficulty in making himself understood, but he would endeavour 

 to say something on Mr. Wrightson's paper. He thought they 

 were indebted also to their friend Mr. Bell for having taken up 

 the question experimentally. Mr. Bell's results were to a certain 

 extent confirmatory of Mr. Wrightson's, and opposed to the 

 hypothesis brought forward some years ago before the Royal 

 Society by Mr. Mallet. There seemed to be now no doubt that 

 cast iron expanded in setting, and that it followed the general law 

 of solids in contracting with diminution of temperature only after 

 it had set. That was in itself a very important fact, and with its- 

 assistance they might be able to discover the true cause of such a 

 physical phenomenon. Mr. Bell had a difficulty in accounting to 

 the full for Mr. Wrightson's assertion that a metal ball floated on 

 the surface when at a considerably lower temperature than that 

 which would follow from the physical consideration brought before 

 them by Mr. Bell. It appeared to D\ . Siemens, however, that Mr. 

 Bell might have added one other cause to those which he had very 

 ingeniously mentioned to account for his brick of partially heated 

 metal rising to the surface much sooner than it could be expected 

 to do, judging simply by the fact of its expansion by heat. Mr. 

 Bell assigned the action partly to the occlusion of gas on the surface 

 of the solid. No doubt that was a good reason, but it was a 

 reason which would apply more forcibly to small balls or pieces of 

 metal than to large ones ; and so far as they could learn, the 

 phenomenon was not influenced in any sensible degree by the 

 volume of metal they were dealing with. Mr. Bell also brought 

 forward a reason, which to Dr. Siemens's mind did not apply- 

 namely, that the currents of hot fluid metal set up in a bath would 



* Excerpt Journal of the Iron and Steel Institute, 1880, pp. 35-37. 



