322 THE SCIENTIFIC PAPERS OF 



ing first on the outside of the mould offered more resistance there 

 to the motion of the plunger, and the outside thus became com- 

 paratively speaking porous, while the fluid portion in the centre 

 received a larger amount of compression than the outside which 

 had more power of resisting the pressure. The particles of gas 

 entangled within the fluid mass would therefore encounter rather 

 less resistance towards the outside than towards the inside, the full 

 hydraulic pressure being transmitted to the centre of the fluid 

 mass. In that way the expulsion of the gases from the fluid 

 metal might perhaps be accounted for ; and he should be glad if 

 Sir Joseph Whitworth would give his explanation of the matter. 

 The fact being admitted, it was clear that the steel produced by 

 that mode of treatment must possess many great advantages 

 over metal treated in the ordinary way by hammering ; for it 

 was hardly to be supposed that hammering would be capable of 

 driving out the gases. 



With regard to the mode in Avhich these gases entered the 

 metal, he did not think they were merely entrapped mechanically 

 at the time of pouring out the metal into the mould ; because in 

 working melted steel in the open hearth of a regenerative furnace 

 he had found that the metal could be made at any moment to 

 evolve gases in great quantities by simply plunging a cold bar of 

 iron to the bottom of the fluid mass. The fluid metal evidently 

 absorbed carbonic oxide to a very great extent ; and it was due to 

 the partial congelation of the metal that the gases were suddenly 

 set free. Similarly in the Bessemer process a great ebullition took 

 place on pouring the fluid metal out of the converting vessel into 

 the iron moulds, and the top of the moulds had to be closed by a 

 stopper to prevent the metal being thrown out by the ebullition. 

 It was clear therefore that the metal contained a large quantity of 

 gas occluded within itself ; and if this was retained in the metal 

 it became a source of weakness. However small the bubbles of 

 gas might be, their presence would have the same effect as the 

 presence of particles of foreign matter between the particles of 

 metal, and must necessarily weaken it. 



In reference to the proposal to designate as steel any metal 

 bearing a tensile strain of 28 tons per square inch, he thought it 

 would be wise on the whole to fix a limit of strength, but some 

 further limitation seemed also to be needed. For instance, a 



