ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 123 



iron-carbon phase. When hardened steel is tempered, the change in 

 physical properties precedes the change in carbon condition. Thus, 

 when a 0*95 p.c. carbon steel quenched in water from 900° C. was re- 

 heated to 400° C, 70 p.c. of the loss of hardness had taken place, and 

 only 1:5 p.c. of the change from hardening carbon to cementite had 

 occurred. Osmondite, the chief constituent when the change has pro- 

 ceeded thus far, is defined as a solid solution of iron carbide in a- iron. 

 Doubt is thrown on the suggestion that the hardness of osmondite, 

 which is still distinctly harder than pearlite, is due to " inequiaxing " 

 (distortion of the crystalline grains). 



Apparatus for Polishing Metal Sections.* — K. W. Zimmerschied 

 describes a machine designed for the use of a number of students. 

 The ten horizontal polishing wheels are driven from two shafts run- 

 ning below the bench. The spindle of each polishing wheel carries at its 

 lower end a friction disk, which can be raised out of contact with the 

 driving wheel on the shaft, thus stopping the polishing wheel. Speed is 

 regulated by sliding the driving wheel along the shaft. Each polishing 

 wheel is provided with a water-guard, and is continuously supplied 

 with distilled water from a glass nozzle. The metal section, after sur- 

 facing on a fine carborundum wheel, is polished in turn with (1) very 

 fine carborundum powder on a canvas-covered disk ; (2) alumina on 

 broadcloth ; (3) if still finer polishing is required, ronge on broadcloth. 



Annealing of Sterling Silver.f — W. H.Walker found that the 

 dark "fire-surface " produced on silver containing 7*5. p.c .copper, by 

 annealing, was due to the oxidation of the copper. By annealing in a 

 non-oxidising atmosphere this surface darkening may be prevented. 

 Sterling silver which has been partially oxidised and afterwards annealed 

 in a reducing atmosphere, shows blisters on the surface, apparently 

 caused by the formation of water vapour within the metal. 



Tellurium-tin Alloys.:}: — H. Fay has determined the freezing-point 

 curve, and studied the microstructure. One compound, SnTe, melting 

 at 769° C, occurs, and forms a eutectic with tellurium, containing 

 85 p.c. of that metal, melting point 399° C, and a eutectic with tin of 

 very low concentration in tin. 



Longitudinal Impact of Metal Rods.§ — J. E. Sears has determined 

 the velocity of propagation of elastic waves in rods of steel, copper, and 

 aluminium, by a dynamical method. Two equal rods of the metal were 

 suspended horizontally by cords, with their ends (made slightly convex) 

 just touching and their axes in the same straight line. One rod was 

 withdrawn a given distance and allowed to swing against the other. 

 The duration of longitudinal impact was measured by allowing an 

 electrical circuit to be completed by the contact, and measuring the 

 total quantity of electricity passing during contact. The results are in 

 very close agreement with the velocities calculated from the formula 



v = \/ —, subjected to a small correction to give the true adiabatic 

 v p 



* Journ. Amer. Cheni. Sec, xxix. (1907) pp. 855-8 (3 figs.). 



+ Tom. cit., pp. 1198-1201 (3 figs.). J Tom. cit., pp. 1265-8 (1 fig.). 



§ Proc. Camb. Phil. Soc, xiv. (1907) pp. 257-86 (9 figs.). 



