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Professor W. Chandler Roberts- Attsten [March 26, 



production of complicated forms by forging or by rolling iron and 

 steel and other metals, entirely dej)ends on the flow of the metal 

 when suitably guided by the artificer. The lines of flow in iron 

 may be well shown by polishing a surface of the metal, and by 

 submitting it to the action of a solution of bichloride of mercury, 

 which etches the surface, or better, to the slow action of chromic 

 acid solution, as suggested by Sir Frederick Abel, the result in 

 either case being, that any difference in the hardness of the metal 

 or in the chemical composition, or want of continuity, caused by 

 the presence of traces of entangled slag, reveals the manner in 

 which the metal has flowed. The engravings illustrate the direc- 

 tion of flow in the following cases. Fig. 4 is a section of a 



Fig. 4. 







forged crosshead, kindly sent me by Mr. Webb of Crewe. Fig. 5 

 represents the top, planed and etched, of a hemisphere of mild 

 steel, of the form and dimensions shown in the sectional view, 

 Fig. 6, I in. thick, " dished " cold by forcing a plate through a 

 circular orifice. The convolutions of the etched portions afford 

 evidence of the struggle sustained by the flowing particles of the 

 metal. The experiments of M. Tresca were not made on " cinder- 

 free " metal ; it is therefore interesting to compare the etched 

 section of the old rail. Fig. 7, the result of the complicated 

 welding of puddled iron, with a basic -Bessemer rail, rolled from 

 steel Avhich has been cast, and which is therefore free from entangled 

 slag. Fig. 8 represents a section of such a rail presented to mo 

 by Mr. P. C. Gilchrist. 



A very striking illustration of the importance of the flow of 

 metals, when used in construction, is afforded by some observations 



