PLATE 29. 



Micro-metallography. 



A MILD STEEL x 50 (carbon 0.25 per cent.). 



Specimen polished, and etched with saturated solution of picric 

 acid in alcohol, shows sorbitic pearlite with ferrite meshing. 



B MONEL METAL (copper nickel alloy) x 150 (33 per cent, copper, 

 64 per cent, nickel). 



Etched by an electrolytic method, the ordinary methods being 

 unsuitable. The alloy was connected to the anode in dilute sulphuric 

 acid. 



Vertical camera used, and cover glass nose-piece illuminator. 



Preparation o/ steel surface (Stead's method). The surface is first 

 levelled by rubbing down by hand on a smooth file, the latter being 

 laid flat on a table. Then on a fairly smooth English emery cloth, 

 next on two or three French emery papers of increasing fineness, and 

 finally polished on a revolving block over which is stretched black 

 cloth impregnated with diamantine powder. 



Photos. Kindly supplied by L. ARCHBUTT, Esq. [To follow page 202. 



