342 SUMMARY OF CURRENT RESEARCHES RELATING TO 



5. Cementite, i.e. the separated carbide of iron, Fe 3 C ; occurs in 

 steels rich in carbon. 



6. Martensite ; probably a solution of Fe 3 C in iron ; occurs only in 

 steel hardened above 600° or 700° C. 



7. Austenite, an alloy rich in carbon, less bard than 5 and 6, and, 

 in the author's opinion, a solution of elementary carbon in iron ; as yet 

 has been only found in steel containing over 1 p.c. of carbon, and 

 suddenly cooled from a high temperature. 



8. Pearlite, a mixture of ferrite and cementite, to which perhaps 

 may be added sorbite ; it may be lamellar or granular. 



9. Sorbite appears, under certain conditions in pearlite as a third 

 constituent ; it may be some residual martensite, which did not have 

 time to be decomposed into ferrite and cementite. 



10. Troostite is found as a jagged and stringy constituent between 

 martensite and cementite, and may hold a relation to these constituents 

 similar to that held by ferrite to cementite in pearlite. 



Microstructure of Manganese Steel.* — Mr. F. C. Lau illustrates by 

 four photomicrographs the appearance and disappearance of certain 

 mysteiious dark discs in quenched manganese steel. He believes that 

 these discs are composed of cementite which, in the case of manganese 

 steel, would be a double carbide of iron and manganese. He has 

 occasionally noticed a similar appearance in carbon steels, with the dif- 

 ference that the discs appear white and brilliant. 



Microscopic Structure of Gold and Gold Alloys.f — Thos. Andrews 

 finds, by means of numerous etchings and micrometer measurements, 

 that pure gold crystallises in the regular cubic system and its modi- 

 fications. 



Gold alloyed with bismuth, lead, silicon, tellurium, or potassium, was 

 also examined, the composition being generally 99 '80 p.c. of gold to 

 0*20 of the baser metal. In all cases crystals of pure gold were found 

 to be imbedded in a more or less intricate rneshwork of alloy, thus 

 throwing light upon the known changes in its physical properties. This 

 alloy is the eutectic. The author discusses the views of other writers 

 on gold alloys. 



Microstructure of Alloys of Iron and Nickel.J — M. Osmond finds 

 that these alloys may be divided into three groups : — (1) those not con- 

 taining above 8 p.c. of nickel ; (2) those containing from 12 to 25 p.c. of 

 nickel ; and (3) the non-magnetic alloys containing about 25 p.c. of 

 nickel, and those which resume their magnetic properties owing to an 

 excess of nickel (30 to 50 p.c). The author finds that the study of the 

 microstructure of these alloys confirms the classification based on their 

 mechanical properties. Additional evidence is afforded that the principal 

 properties of steels are a function of the position of their points of trans- 

 formation on the scale of temperature. Alloys of iron and nickel are 

 also found to acquire the interesting property of schistosity under 

 forging. This is revealed by all etching methods, giving rise to the 

 formation of bands alternately more or less attacked, surrounding each 



• Metallographist, i. (1899) pp. 1537-9 (4 figs.). 



t Tom. cit., pp. 105-25 (10 li-s). 



X Comptes Rendus, May 9, 1898; and Metallographist, i. (1899) pp. 69-71. 



