268 SUMMARY OF CURRENT RESEARCHES RELATING TO 



various grades of emery, etc., with selvyt or other method, friction 

 should be given with the ball of the thumb, following which rice-starch, 

 previously ground to a very fine powder, should be rubbed on with 

 medical (but not medicated) wool — such as the pure wool sold by the 

 chemist. Where this is not practicable, a piece of soft razor-strop 

 leather, or a strip of selvyt glued on a piece of smooth hard wood, may 

 be employed, using the starch plentifully. The starch must be used so 

 plentifully that it does not get heated. The writer has used both pro- 

 cesses for a long time past in metallography with the greatest success. 



Metallography, etc. 



Aluminium-silver Alloys.* — W. Broniewski has determined the elec- 

 trical conductivity, the temperature-coefficient of electrical resistance, 

 the thermo-electric properties, and the E.M.F. of solution, of a series of 

 aluminium-silver alloys. The curves expressing the results indicate the 

 existence of the compounds Al. 2 Ag 3 and A!Ag 3 . Confirmation was 

 obtained by microscopical examination of the alloys. 



Quenching of Bronzes.f — The softening effect of quenching cast- 

 bronze from a suitable temperature appears to be due to the suppression 

 of the decomposition of a solid solution. L. Grenet points out that if 

 this explanation holds, subsequent re-heating of such softened material 

 should cause an increase in hardness by bringing about the decomposition 

 of the solid solution. Two tin-copper alloys, containing respectively 

 15 and 20 p.c. tin, were softened by quenching from 750° C, and, as 

 anticipated, the hardness was restored by subsequent re-heating at tem- 

 peratures 100° to 400° C. 



Bearing Metals. + — A. Hague discusses the qualities desirable in 

 bearing metals, and classifies the alloys used for this purpose as : (1) rigid 

 bronzes ; (2) plastic white metals ; (3) plastic bronzes. The plastic white 

 metals consist of hard grains embedded in a plastic matrix. In the third 

 class, plasticity is imparted to the bronzes by the addition of 15 to 30 p.c. 

 of lead.*^ The lead does not appear to alloy with the bronze, but to be 

 held mechanically ; it exists in the bearing metal as veins of lead. The 

 composition and properties of numerous anti-friction alloys are given, 

 with much information on the best methods of employing them. 



Behaviour of Copper towards Gases.§ — A. Sieverts and "W. Krumb- 

 haar have investigated the solubility, in solid and in molten copper, of 

 oxygen, nitrogen, carbon monoxide, carbon dioxide, hydrogen, and 

 sulphur dioxide. The behaviour of hydrogen points to the existence 

 of a solid solution of hydrogen in copper. 



* Comptcs Rendus, cl. (1910) pp. 1754-7 (4 figs.). 



t Op. cit., cli. (1910) pp. 870-1. 



X Engineering, lxxxix. (1910) pp. 826-9. 



§ Zeitschr. Phys. Chem., lxxiv. (1910) pp. 277-307 (4 fige.). 



