674 SUMMARY OF QUERENT RESEARCHES RELATING TO 



Industrial Application of the Microscope.* — W. H. Davis describes 

 the method of employing the Microscope in controlling the roasting 

 of ;i sulpho-telluride gold ore, chemical analysis failing to give sufficiently 

 deli ii ilr information as to the relation between the condition of the gold 

 and the roasting temperature. 



Illumination in High-power Photomicrography. - ]- — C. Benedicks 

 points out that published metallographical photomicrographs at 1000 

 or more diameters, with a few exceptions, leave much to be desired in 

 sharpness of definition. This appears to be due to the neglect of an 

 important factor. The Beck illuminator, a thin glass plate setatanangle 

 of 45° in the Microscope tube, has, on account of certain disadvantages, 

 been replaced to a large extent by the Zeiss or Nachet prism. Such 

 totally-reflecting prisms cut off one-half of the light rays proceeding 

 from the objective, and the author proves that this is equivalent to a 

 large reduction in numerical aperture. Tests of a Zeiss 2 mm. apo- 

 chromat N.A. = 1 "SO, with and without a piece of black paper fixed above 

 one half of the objective, were made on various test-objects viewed by 

 transmitted light. The resolving power was greatly reduced by the 

 presence of the paper. Photomicrographs at 1200 diam. are given of 

 the same field of lamellar pearlite illuminated (1) by a reflecting prism ; 

 (2) by a cover-glass at 45° ; (3) as (2), but with one-half of the cone of 

 light cut off by a diaphragm placed above the glass disk ; (2) showed 

 much sharper definition than either of the other two photomicrographs. 

 The faults of the Beck illuminator are shown to be not serious : it is 

 accordingly to be preferred to the prism for high-power work. 



Autographic Registration of Cooling Curves.! — E. F. Northrup 

 describes a sensitive autographic recorder to be used with a resistance 

 pyrometer. The author discusses I, lie various methods of taking cooling 

 curves, and concludes that the direct time-temperature curve gives all the 

 information required. 



Measurement of Hardness. — P. Ludwik § submits the official report 

 to the Copenhagen Congress. Only those methods which have been 

 extensively introduced into technical practice are dealt with — the ball- 

 pressure and cognate cone-pressure tests. 



A. Martens and E. Ileyn || recommend the measurement of depth of 

 impression rather than diameter in the ball-hardness test, and describe a 

 machine for impressing the ball into the test-piece and measuring the 

 depth with great accuracy. 



A. (iessner^ has investigated the relation between hardness (as 

 measured by the cone-pressure test) and tensile strength of permanent- 

 way materials. 



II. Moore** has determined the limiting conditions (minimum thick- 

 ness and diameter of -test-piece permissible) for the ball-pressure hardness 



* Metallurgie, v. (1908) p. 734 (4 figs.), 

 t Op. cit., vi. (1909) pp. 320-3 (3 figs.). 

 % Electrocbem. and Met. Ind., vii. (11)09) pp. 273-4 (1 fig.). 

 § Proc. Int. Assoc, for Testing Materials, No. 6 (1909) 12 pp. (5 figs.). 

 || Tom. cit., 10 pp. (6 figs.). ^ Tom. cit., 2 pp. 



** Op. cit., No. 9, 11 pp. (1 fig.). 



