222 SUMMARY OF CURRENT RESEARCHES RELATING TO 



If the highly heated steel be suddenly cooled by quenching in ice-cold 

 water, ferrite, pearlyte, and cementito disappear. Two cases now present 

 themselves, according as the carbon content is inferior or superior to that 

 of the eutectic alloy. Thus, in a piece of steel containing • 45 p.c. of 

 carbon, and cooled as described, we find a constituent, probably homo- 

 geneous, made up of needles, parallel in the same region, but frequently 

 crossing one another along three principal directions. It is called 

 martensite. The needles of martensite, other conditions remaining the 

 same, become smaller and less distinct as the composition of the eutectic 

 alloy is reached. Its hardness increases simultaneously up to its maximum. 

 Above that point the metal does not remain homogeneous. A steel with 

 1*5 p.c. of carbon, quenched at 1050° C. in ice-water, breaks up into 

 two constituents (plate IV. fig. 2). One of tbem (austenite, the light 

 portion) possesses the unexpected property of being soft enough to be 

 scratched by a sewing-needle. 



Microscopic Study of Metallic Alloys.* — M. Charpy, of Paris, de- 

 scribes his experiments with alloys. In preference to working with 

 commercial alloys, which are apt to be of complicated composition, he 

 selected those of the simplest known type, which were more likely to 

 yield phenomena in a more suggestive form. His conclusions with 

 regard to eutectic alloys were that they were analogous to cryohydrates, 

 which Ponsot ascertained, in 1895, were composed of juxtaposed crystals 

 alternately of ice and of solid salt, the latter anhydrous or hydrated. 

 Thus in examining the eutectic alloy of tin and bismuth (Sn 53 ■ 9, Bi 

 46 • 1 p.c), the crystals were found extremely minute, but the metals 

 were simply juxtaposed. Plate V. fig. 1 shows one of these prepara- 

 tions magnified 200 diameters ; the black portions indicate the bismuth, 

 the white areas the tin which had been dug out by the dilute hydro- 

 chloric acid. Fig. 2 shows an alloy of silver and antimony (Ag 66, Sb 

 34 p.c.) magnified : the preparation has been treated with hydrosulphuric 

 acid, which darkens the silver without affecting the antimony. The 

 silver is represented by the white portions. The alloy is made up of 

 large areas of silver surrounded by the eutectic alloy, which clearly 

 exhibits the alternate layers of silver and antimony. 



The conclusion, therefore, is that eutectic alloys exist in the solid 

 state as simple mixtures of their constituents. 



The author also describes similar experiments with alloys having 

 normal curves of fusibility. 



The second portion of the paper deals with alloys with abnormal 

 curves of fusibility. These include alloys of copper and tin, antimony 

 and tin, antimony and silver, copper and zinc, silver and tin, and silver 

 and zinc. These are all discussed, and 17 excellent photomicrographic 

 figures illustrate the relations of the respective eutectic alloys to the 

 matrices. 



Crystalline Structure of Metals.f — In the Bakerian Lecture, Messrs. 

 Ewing and Rosenhain discuss fully their previous experiments on this 

 subject, and confirm their conclusion, to the effect that the plasticity of 

 metals is due to the sliding over one another of the crystalline elements 



* Metallographist, i. (1898), pp. S7-106 (12 figs, and 2 diagrams); pp. 192-210 

 (17 figs.). t Proc. Roy. Soc, lxv. (1899) pp. 172-7. 



