288 Transactions of the Society. 



stain is readily removed by slight friction, the lines appear white 

 on a dull ground. 



Professor Heyn has kindly sent me some photographs of steel 

 structures developed by his copper-ammonium-chloride reagent, 

 which appeared to be identical with those developed by iodine. 

 Although he does not describe them as other than indicative of 

 primary crystallisation, I have but little doubt that they are 

 mainly evidence of imperfect distribution of phosphorus. 



If steel, containing low carbon, say under * 5 p.c, in either the 

 cast or forged condition, is very slowly cooled, the highly phos- 

 phorised areas reject the carbon which had segregated with the 

 phosphorus, and as a result massive areas of ferrite appear, the 

 borders of which are often surrounded with pearlite. 



If the phosphorus is greatly concentrated in certain parts, 

 carbon will not be retained there even on comparatively rapid 

 cooling from a high temperature (pi. VI. fig. 11). 



Description of the Photo-Microgkaphs. 

 Plates V. and VI. 



Fig. 1. — Heavy steel forging showing white parallel streaks, 

 similar to those described by Signor Schanzer, etched with iodine. 



Fig. 2. — Photograph of rolled soft steel bar, by Professor E. 

 Heyn, etched with the Heyn reagent. The dark central portion is 

 highest in phosphorus. 



Professor Heyn states that etching alone enables one to deter- 

 mine that the central portion is highest in phosphorus. 



Fig. 3. — Steel casting containing 0*3 p.c. carbon, 0*057 p.c. 

 sulphur, and • 041 p.c. phosphorus. Heat-tinted to a brown colour. 

 The high lights indicate specks of sulphide of manganese (MnS), 

 the half-tone parts are the boundaries of crystals highest in phos- 

 phorus. The dark background is ferrite and pearlite. In the 

 object itself the ground mass is brown, the phosphoiised parts are 

 purple, and the sulphide of manganese is white. After forging to 

 one-third of the original diameter, the phosphoiised parts appear 

 as bands, and are readily detected by heat-tinting, or by slight 

 etching with iodine. 



Fig. 4. — The same steel as fig. 3, to which phosphorus was 

 added when fluid to give ' 3 p.c. Structure developed by heat- 

 tinting. The whiter parts are the boundaries of the primary 

 crystals, and are very high in phosphorus. 



Fig. 5. — The same steel as the last, after forging to one-third of 

 the diameter. Heated rapidly to blue and etched with very dilute 



