102 - SUMMARY OF CUERENT RESEARCHES RELATING TO 



Metallography, etc. 



Heterogeneity of Steels." — By treating polished sections of steel 

 with a cupric reagent and then removing the deposited copper by solu- 

 tion in ammonia, 6. Charpy and S. Bonnerot find that pearlite appears 

 white and ferrite darli, i.e. the appearance is the reverse of that 

 obtained l^y etching with ordinary reagents, such as nitric or picric 

 acid. The parts which are darkened are those which receive the first 

 deposit of copper, even in samples which appear to have received an 

 almost uniform coating of copper. The selective action of the cupric 

 reagent is determined mostly by the phosphorous and other elements 

 in the ferrite, and not by the carbon, as with acid reagents. The 

 dendritic structure of cast-steel is shown very clearly by this method of 

 etching, the dendrites appearing white and the remainder of the mass,, 

 which has solidified later and contains the greater part of the foreign 

 elements, dark ; and the authors have used it to trace the progressive 

 deformation of the dendrites during rolling of the steel. The dimen- 

 sions of the dendrites and their variation with conditions of cooling 

 were also studied. Variations in size of ingot have little effect on the 

 size of the fine dendrites formed by contact with the walls of the ingot- 

 mould ; those which form in the centre of the ingot increase considerably 

 in size with increase in size of ingot. In ingots of relatively pure steel 

 and of medium size, variations of 1 to 10 in the relative size of the 

 dendrites in the peripheral and central portions were observed. 



Tungsten-Molybdenum Alloys, f — Alloys of tungsten and molyb- 

 denum were prepared by Z. Jeffries by mixing the powdered metala 

 (obtained by reduction of the oxides in hydrogen) in the requisite 

 amounts, pressing into briquettes and sintering in hydrogen at 1300° C,,. 

 and then heating just below the fusion temperature (previously deter- 

 mined approximately) for twelve minutes. After such treatment the 

 alloys were completely crystalline, and could be rolled or drawn. The 

 melting-points were determined by a novel electrical method, depending^ 

 on the number of watts consumed in melting a wire in an atmosphere 

 of hydrogen, the melting-points and fusion-wattage of the pure metals- 

 being known. The melting-point curve shows that the alloys form a 

 continuous series of solid solutions. This was confirmed by microscopical 

 examination of the structure of the alloys. AVhen properly prepared, all 

 consisted of homogeneous polygonal crystals. The alloys were etched 

 with a boiling solution of hydrogen peroxide. Examination of etching- 

 pits in the pure metals showed that they both crystallized in the iso- 

 metric system, the crystal units being cubes. 



* Comptes Eendus, clxv. No. 17 (1917) pp. 536-40 (6 figs.). 



t Trans. Amer. Inst. Mining Engineers, No. 115 (1916) pp. 1225-36 (11 figs.). 



