ZOOLOGY AND BOTANY MICROSCOPY, ETC. 387 



Metallography, etc. 



Properties of Gold Leaf at High Temperatures.*— J. C. Chapman 

 and H. L. Porter have found that gold leaf does not become transparent 

 when heated alone. When gold leaf, suspended from a horizontal wire 

 and maintained in tension by means of a small weight hung on it, was 

 heated, a gradual increase of length took place up to about 170° C. 

 From 170° to 340° C. the length remained constant, and at 340° C. a 

 rapid contraction began and continued through a considerable tempera- 

 ture interval. Gold leaf fixed to glass remained unchanged when heated 

 a few degrees below 340° C, but when heated a little above 340° C. it 

 became transparent. Microscopic examination showed that the gold 

 itself was still opaque, but had aggregated, leaving clear spaces, as 

 observed by Turner, f The contraction appears to be the cause of the 

 transparency. 



Microstructure of Copper.! — A metallographical study of copper 

 containing various amounts of impurities forms part of an investigation 

 of the oxidation refining process by TV. TVanjukoff. The samples were 

 taken at different stages in the refining operation. Four etching reagents 

 were used : (1) Ammonia solution ; (2) ammoniacal solution of copper 

 chloride ; (3) nitric acid of 1 • 2 sp. gr. ; (4) copper sulphate solution, 

 acidified with sulphuric acid, in which the section was made the anode 

 of a weak electric current. Numerous photomicrographs illustrate the 

 paper. 



Copper-aluminium Alloys.§— M. Barree has determined the trans- 

 formation points of the alloys in the range 8 to 15 '5 p.c. aluminium, 

 by measuring the variation of electrical resistance with temperature. 

 Critical points were found in the neighbourhood of 500° and 750° C, 

 sufficiently near to those found by L. Guillet. In addition, a new 

 critical point was observed at about 200° C. In those cases in which 

 the transformation did not occur at exactly the same temperature on 

 heating and on cooling, the critical point on cooling was the lower. 

 Successive heatings did not affect the position of the critical temperatures. 



TV. Broniewski|| has determined the specific conductivity, the tem- 

 perature-coefficient of the resistance, the thermo-electric properties and 

 the solution E.M.F. of the complete series of alloys of aluminium with 

 copper. The curves embodying the results obtained point to the exist- 

 ence of the compounds Al 2 Cu, AlCu, Al 2 Cu 3 , and AlCu 3 . Of these, 

 Al 2 Cu 3 is new, while the existence of AlCu has been disputed. 



Alloys of Nickel and Copper. IF— E. Vigouroux has not succeeded in 

 isolating any definite compounds by the chemical treatment of nickel- 

 copper alloys. An investigation of the E.M.F. of solution of these 

 alloys leads to the same conclusion, that no compounds exist. 



* Proc. Roy. Soc, Series A, lxxxiii. (1909) pp. 65-8 (2 figs.). 



+ See this Journal, 1909, p. 117. 



% Metallurgie, vi. (1909) pp. 749-59, 792-801 (55 figs.). 



§ Rev. Metallurgie, vii. (1910) pp. 16-33 (S figs.). 



|| Comptes Rendus, cxlix. (1909) pp. 853-5. f Torn, cit., pp. 1378-80. 



2 D 2 



