ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1 17 



Transparent Metallic Films.*— T. Turner finds that thin films of 

 gold, silver, or copper, heated in air between glass slips, become trans- 

 parent at temperatures below 550° C. In the case of gold and silver, 

 microscopic examination proves that the apparent transparency is due 

 to destruction of continuity of the film, the metal aggregating when 

 heated into separate granular masses. Under similar conditions copper 

 oxidises, forming a continuous transparent film, bright green at first, 

 then gradually darkening to deep brown. The discovery of a trans- 

 parent stage in the oxidation of copper supports the view thai the 

 spectrum colours, which appear on the surface of certain metals by 

 -oxidation, are due to the formation of a transparent film. 



Structure of Eutectics.f — As a preliminary to the study of a pure 

 eutectic alloy, W. Rosenhain and P. A. Tucker have re-determined the 

 equilibrium diagram of the lead-tin system. $ The eutectic point is 

 placed at a concentration of 63 p.c. tin. Transformations of the lead- 

 rich alloys, occurring in the solid state, are regarded as the separation of 

 tin from the solid solution of tin in lead, which changes from the /? to 

 the a state. The eutectic consists of grains, in each of which there is a 

 systematic orientation of the laminations produced by layers of the two 

 constituents. The authors take the view that these grains are true 

 spherulitic crystals. 



Partition of Silver between Zinc and Lead.§ — G. N. Potdar has 

 investigated the constancy of the partition coefficient of silver between 

 liquid zinc and liquid lead. Weighed quantities of the three metals 

 were maintained at 540° C. for several hours, the mass was allowed to 

 solidify, and the percentage of silver determined in each of the two 

 layers. The separation of the lighter and heavier layers was not quite 

 perfect : this caused discrepancies in the results. The author concludes 

 that the coefficient is constant for the more dilute solutions, and is 

 about 300. The partition coefficient of silver between solid zinc and 

 liquid lead (of importance in the Parkes process), is much higher. 



Troostite.|| — C. Benedicks defends the appellation " colloidal solu- 

 tion " as applied to troostite, on the ground that dispersed systems 

 containing ultramicroscopic particles of metals are universally admitted 

 to be colloidal solutions. H. le Ohatelier considers that the expression 

 " colloidal solution" must fall out of use, since the condition indicated 

 is not one of solution in any true sense. 



* Proc. Roy. Soc, Series A, lxxxi. (1908) pp. 301-10 (9 figs.). 



t Tom cit., pp. 331-4 (1 fig.). 



t See this Journal, 1908, p. 523 



§ Journ. Coll. of Sci. Tokyo, Japan, xxv. (1908) Art. 9 (4 figs.). 



j| Rev. Metallurgie, v. (1908) pp. 878-9. 



