ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 711 



tions are intimate crystalline mixtures ; whilst the primary crystals are 

 too small to be detected microscopically, they are large enough to retain 

 their identity ; (2) the term "solid solution" is strictly not applicable 

 to crystalline bodies such as metallic alloys, and should be restricted to 

 supercooled liquids, such as glass. 



Alloys of Aluminium and Zinc* — W. Rosenhainand S. L. Archbutt 

 have re-determined the equilibrium diagram of the aluminium-zinc 

 system. Cooling curves and some heating curves were taken ; 300 grm. 

 of alloy were used for each experiment, and the rate of cooling was slow. 

 Microscopic examination was applied to specimens which had been (1) 

 slowly cooled from fusion, (2) annealed at certain definite temperatures, 

 and either slowly cooled, or quenched. The diagram differs in impor- 

 tant features from that given by Shepherd. The existence of the 

 compound Al 2 Zn 3 (corresponding to the J3 phase) has been demonstrated. 

 In alloys containing this phase, dendritic crystals frequently assuming 

 six-rayed forms were observed. A horizontal line in the diagram at 

 about 440° C. is held to represent the formation of Al 2 Zn 3 , while a hori- 

 zontal at about 255° C. represents the decomposition of that compound. 



Aluminium Alloys containing Magnesium. f — A. Wilm finds that 

 certain aluminium alloys containing a small amount of magnesium are 

 capable of being hardened by heat-treatment. Immediately after 

 quenching, the alloy is soft, but after a few days at atmospheric tempera- 

 ture its hardness rises considerably. An increase in ductility accompanies 

 this increase in hardness. The hardness attained upon storage increases 

 with rise of quenching temperature, up to 470° C. An alloy containing 

 8 ' 5 p.c. copper, ■ 5 p.c. magnesium, after being hardened by storage 

 following quenching, was considerably further hardened by cold-rolling. 

 The addition of a small quantity of manganese to such alloys renders 

 them capable of resisting the destructive action of mercury, as the surface 

 is not wetted by mercury. 



Lead-tin Alloys. J — D. Mazzotto has made a careful study of the 

 heat-evolution in the solid state which occurs at about 150° C. in lead- 

 tin alloys on cooling. In an alloy containing 33 • 3 p.c. tin and 66 ' 7 p.c. 

 lead, it was found that the intensity and the temperature of the recales- 

 cence phenomenon were considerably affected by previous annealing, the 

 maximum values of both temperature and intensity being obtained by 

 annealing at 188° C, the eutectic temperature. The temperature of 

 maximum intensity, and the heat of transformation, rise with increase 

 of tin content up to 18 p.c. tin, which is the concentration of the solid 

 solution saturated at the eutectic temperature. The author shows that 

 the thermal phenomenon in question may be fully explained by the rapid 

 diminution of the solid solubility of tin in lead as the temperature falls 

 below the eutectic temperature. The evolution of heat on cooling is 

 caused by the falling of tin out of solution in lead. Annealing tends to 

 increase the quantity of solid solution which is saturated at the annealing 



* Proc. Roy. Soc, Series A, lxxxv. (1911) pp. 389-92 (1 fig.). 



t Metallurgie, viii. (1911) pp. 225-7 (9 figs.). 



t Int. Zeitschr. Metallographie, i. (1911) pp. 289-352 (8 figs.). 



