ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 509 



probably smaller at higher temperatures. Crystallised y-iron may con- 

 tain up to 11) p.c. tin ; the solubility of tin in a-iron is not appreciably 

 diflferent. The temperature of magnetic transformation of iron does not 

 appear to be affected by additions of tin or gold. Tin and iron form at 

 least one compound (at S!)3° C.) ; its exact composition is not established. 

 Iron and gold give a homogeneous melt in all proportions. They form 

 no compounds. The solubility of gold in iron and of iron in gold in 

 the solid state falls considerably with falling temperature. 



Iron-carbon Alloys.* — P. Goerens develops the theory that graphite 

 never separates from the melt as such, but is invariably the product of 

 the decomposition of cementite in the solid state. While the stable 

 system is iron + carbon, iron + cementite being metastable, the accepted 

 diagram represents the equilibrium between iron and cementite. In the 

 molten alloys the carbon exists as carbide. The eutectic at 4*2 p.c. 

 carbon solidifying at ll'Mf C, is a mixed crystals -f- cementite eutectic. 

 The formation of kish in high carbon cast iron is explained as follows : 

 On cooling, cementite first separates out from the melt ; this splits up 

 into graphite and iron ; the iron redissolves in the molten solution of 

 cementite in iron, and the flakes of graphite float to the surface. Among 

 the author's experimental work are determinations of melting points of 

 alloys, and investigation of the microstructure after varying heat treat- 

 ment. Of two alloys of the same carbon content, existing in one as 

 cementite, in the other chiefly as graphite, the graphitic alloy has the 

 higher melting point ; the white cast iron begins to melt at the same 

 temperature at which its solidification ceases. A useful table is given 

 showing the action of various etching reagents on the different con- 

 stituents. t 



Copper and Phosphorus.^ — E. Heyn and 0. Bauer have made a 

 complete investigation of the freezing-point curve and the microstruc- 

 ture of the copper-phosphorus alloys. The curve indicates the existence 

 of the compound CugP, confirmed by determinations of density and of 

 E.M.F. against copper in a copper sulphate solution. A eutectic 

 (8*27 p.c. phosphorus, 707° C.) is formed by CugP and a solid solution 

 of very low concentration of CugP in copper. The hardening effect of 

 phosphorus on copper is greater than that of tin ; CugP is very hard. 

 Alloys containing more than 15 p.c. phosphorus cannot be prepared 

 by melting, but by heating copper filings and phosphorus to 300°- 

 400° C, richer alloys result. On raising these richer alloys to higher 

 temperatures they lose phosphorus, a definite concentration corresponding 

 to each temperature. At 1100° C. it is 14*lp.c., i.e. the compound 

 CugP. The alloys over 14 "1 p.c. appear to consist of mixed crystals of 

 CugP and CujP.^. Copper ammonium chloride solution was used for 

 etching the microscopic sections. 



Copper, Silver, and Lead.§ — K. Friedrich and A. Leroux have 

 revised and completed the equilibrium diagrams of the binary systems, 

 copper-silver and lead-copper, and have determined the diagram of the 

 ternary system. Two crystalline phases are found in the copper-silver 



* Metallurgie, iv. (1907) pp. 137-49, and 173-85 (44 figs.). 

 + See also this Journal, 1907, p. 116. 

 t Metallurgie, iv. (1907) pp. 242-7 and 257-66 (30 figs.). 

 § Metallurgie, iv. (1907) pp. 293-315 (83 figs.). 



