222 SUMMARY OF CURRENT RESEARCHES. 



as the coarse crystalline structure of steel in the cast condition ; in 

 hypo-eutectoid steels it is characterized by the presence of primary 

 ferrite, which exists in one of two forms : (1) a network ; (2) as needles 

 in a triangular or " delta " arrangement, constituting the Widmann- 

 statten structure. If steel in the cast condition is heated above Ac 3 

 and cooled slowly, ferrite is re-precipitated more or less upon the lines 

 originally occupied by it in the raw steel. The author's experiments 

 now show that if the coarse casting structure is effaced by heating to 

 900 C. and cooling rapidly, it tends to re-appear if the steel be again 

 heated above Ac-j and cooled slowly. 



New Etching Reagent for Steel.*— W. Rosenhain describes the 

 action of a reagent composed of an acid solution of ferric chloride, such 

 as is used for etching copper alloys, to which have been added about 

 O'l p.c. cupric chloride and 0"05 p.c. stannic chloride. When this 

 reagent is applied to a polished steel specimen, a thin deposit of copper 

 is slowly formed on the ferrite, while pearlite and cementite are only 

 very slightly affected. Under the Microscope the ferrite appears to be 

 blackened, while the pearlite remains bright. In commercial steels the 

 ferrite is not darkened uniformly, a strongly banded structure being 

 developed. Apparently the rate of deposition of copper is greater as the 

 freedom of the ferrite from impurities, especially phosphorus, is more 

 complete. The patterns obtained by the use of the reagent indicate 

 clearly the distribution of the phosphorus, and have been found to be 

 identical with patterns obtained by Stead's " heat-tinting " process. 



Optical Orientation of some Cast Metals. f — K. Endell and 

 H. Hanemann give an account of their applications of Konigsberger's 

 methods by which opaque bodies are microscopically examined in 

 polarized light. Sections are polished by the usual methods, but not 

 etched ; they should show no " relief " effects. According to the 

 character of the light which they reflect constituents, are distinguished 

 as isotropic or anisotropic. The appearances observed in sections of 

 quickly solidified ingots of the anisotropic metals, zinc, antimony, 

 bismuth, and tin, are described. When allowed to solidify without 

 disturbance, zinc and antimony form similarly oriented crystals, having 

 their optical axes at right angles to the cooling surface. Primary 

 crystals of the same metals occurring in a ground mass of eutectic were 

 examined, as were also the various constituents and slag inclusions 

 occurring in steel. 



* Nature, xcii. (1914) p. 529. 



t Zeitschr. Anorg. Chem., lxxxiii. (1913) pp. 267-74. 



