92 SUMMARY OF CURRENT RESEARCHES RELATING TO 



composition of alloys, and describes the procedure he has adopted for 

 the determination of aluminium in zinc-aluminium alloys, of oxygen 

 in copper, and of iron in zinc, by measurements of areas occupied in 

 photomicrographs, by eutectics, or by compounds. The outlines of con- 

 stituents may be traced upon finely ruled squared paper, and the number 

 of squares included in the area counted. In measuring areas occupied 

 by eutectics, coalescence must be taken into consideration. 



Z. Jeffries * has used for the same purpose a vertical photomicro- 

 graphic apparatus having a glass plate, thinly coated on its upper 

 surface with paraffin-wax. in the place of the camera screen. The areas 

 are measured on the waxed surface with a planimeter. The addition 

 of starch to the paraffin-wax increases its opacity and permits the use of 

 a thinner coating. 



Long-focus Microscope, and its Applications in Metallography.! 

 F. Ilobin describes a Microscope designed for the examination of 

 polished sections while they are being heated. By placing an achro- 

 matic biconcave lens in the Microscope tube, just behind the focus of 

 the objective, the magnifying power is considerably increased, and 

 moderately high magnification is obtained without reducing the distance 

 between specimen and objective. Such an instrument, constructed by 

 Nachet, gave a magnification of 200 diam., with a distance between 

 specimen and objective of 5 cm. Oblique illumination is used. When 

 used for the examination of specimens during heating the Microscope 

 is horizontal. The specimen is held in a suitable clamp, heated by a 

 Bunsen burner, and contains a small hole for the reception of a thermo- 

 couple. 



The microscopic appearances during oxidation of various steels, and 

 other metals and alloys, by heating in air are described, and the relative 

 rates of oxidation of the different constituents are shown as curves, the 

 relative thicknesses of the oxidation films being calculated from the wave- 

 lengths corresponding to the colours observed. An allotropic change 

 occurring on heating may make itself evident by a sudden change in 

 the progress of oxidation. The development of the crystal boundaries 

 of metals and alloys during heating has also been studied in the same 

 way. Antimony, bismuth, and zinc exhibited this phenomenon clearly. 

 The visibility of the grain boundaries of a heated specimen appears to be 

 due to an actual difference of level between adjoining crystals. An 

 explanation of the development of this difference in level is suggested, 

 depending on differences in the expansion of the crystals in different 

 directions. The temperatures at which the grain boundaries first 

 appeared were determined for a number of metals and alloys. Observa- 

 tions, by the same method, of appearances during heating connected 

 with the sub-division of the large grains of metals, with the development 

 of fissures, and with fusion are described. 



Improved Vertical Illuminator.^ — F. E. "Wright describes a device 

 fitted to a vertical illuminator of the glass plate type, which enables 



* Met. and Chem. Eng., xi. (1913) p. 668. 



t Bull. Soc. d'Encouragement, cxviii. (1912) pp. 204-31 (22 figs.). 



% Journ. Washington Acad. Sci., iii. (1913) pp. 14-16 (1 fig.). 



