ZOOLOGV AND BOTANY, MICROSCOPY, ETC. 273 



series the results obtained were somewhat different. The manganese 

 had no appreciable effect on the relative proportions of graphitic and 

 combined carbon until 3 per cent, was present. With higher percentages 

 the combined carbon increased at the expense of the graphitic ; some 

 graphitic carbon remained, however, with 17 '5 p.c. manganese. 



Fixing Objects to Stage.* — 0. "Wawrziniok describes a clamp for 

 holding specimens. The clamp is screwed to the microscope stage, has 

 a levelling arrangement for adjusting the level of the polished surface, 

 and has been found useful for holding large objects such as ancient gun- 

 barrels. 



Photomicrographic Apparatus.! — F. Robin describes a number of 

 modifications which he has introduced into the Le Chatelier apparatus. 

 The objective is pointed downwards, and below it on the stage is 

 placed the section with its polished face uppermost. The stage has 

 movements vertically, and in two directions horizontally ; its level may 

 also be adjusted through large angles, and it is capable of carrying 

 large and heavy pieces of metal. The apparatus rests on felt, which is 

 more effective than rubber in deadening vibrations. The source of 

 light is an arc, with carbons set at right angles ; the positive carbon 

 remains in the optical axis, and the crater does not alter its position. 

 All examination is carried out upon the image projected on the ground 

 glass screen of the camera. The focusing movements, as well as the 

 other stage movements, are controlled by means of four horizontal rods, 

 the free ends of which are below the focusing screen. Oblique illu- 

 mination may be secured by moving the condenser and using a small 

 mirror ; transparent objects may be viewed by transmitted light. The 

 author points out that examination by oblique light supplements most 

 usefully the usual examination with vertical illumination ; examples 

 illustrated with photomicrographs are given. The application of micro- 

 chemical analysis in metallography is discussed ; methods and examples 

 are given. A minute quantity of a solution, obtained by placing a drop 

 of an acid or other reagent on a clean surface of the substance to be 

 examined, is treated with reagents on a glass slip ; the products of the 

 reactions are observed microscopically. 



Sulphurous Acid as an Etching Medium. J — S. Hilpert and E. 

 Colver-Glauert, in searching for an etching reagent having a purely 

 chemical action on iron and steel, have found that sulphurous acid may 

 be used with highly satisfactory results instead of the numerous diverse 

 etching media proposed for developing the structure of hardened steel. 

 The action of these reagents, many of which are complex mixtures of 

 organic bodies, is little understood. A useful strength is a 3 to 4 p.c. 

 solution in water of a saturated solution of sulphur dioxide in water, free 

 from sulphuric acid. Etching is complete in from 7 seconds to 1 minute. 



* Metallurgie, vii. (1910) pp. 312-13 (4 figs.), 

 t Rev. Metallurgie, vii. (1910) pp. 903-20 (23 figs.). 



$ Journ. Iron and Steel Inst., lxxxii. (1910) pp. 54-64 (9 figs.) See also Zeitschr. 

 Anorg. Chem., lxviii. (1910) pp. 63-8. 



