ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 407 



Microscopic Examination of Carbon.*— G. A. Roush has applied 

 iiietallograpliieal methods to the examination of carbon electrodes, 

 brashes, and similar electrical material. Polished sections are " etched " 

 by heating to redness so that the more readily oxidized portions are 

 oxidized, or by relief polishing on chamois skin or broadcloth. Petroleum 

 coke can be recognized by a striated appearance, retort carbon by a 

 finely pitted surface. Natural graphites can generally be recognized 

 by the shape of the flakes, but artificial graphites are not readily identi- 

 fied. Photomicrographs are given. 



Grinding- and Polishing Machine. t — A simple and handy machine 

 made by R. and J. Beck is described. A single horizontal brass disk is 

 driven by a small motor. By shifting the belt a range of speeds from 

 800 to 1000 revolutions per minute may be obtained. The emery paper 

 or polishing cloth is stretched over the disk and held by means of a 

 garter made of a stiff brass spiral spring ring fitting into a groove in 

 the edge of the disk. 



A removable splash-guard is provided, and a cover for excluding 

 dust when the machine is not in use. 



Reflex Camera for Photomicrography. $ — 0. Heimstiidt describes 

 a photomicrographic camera made on the reflex pirincipleby C. Reich ert. 

 It is claimed that the effects of vibration, so troublesome in high power 

 work, are minimized by the use of this apparatus. 



Polyhedric Structure in Iron-carbon alloys.§ — X. J. Wark has micro- 

 scopically examined seven iron-carbon alloys, containing ' 1 to 1 ' 7 p.c. 

 carbon, quenched at various temperatures in the range 800-1400° C. 

 Certain of these contained large polyhedra. A similar series of five 

 alloys were etched with hydrochloric acid gas at high temperatures 

 (850-1050'" C.) ; within the solid solution field, the structures developed 

 were always polyhedric. The polyhedric structure appears to be that of 

 the original austenite solid solution. 



Critical-point at 470° C. in Copper-zinc Alloys. |1 — H. C. H. 

 Carpenter has continued his investigation of the /8 constituent in the 

 copper-zinc system. A specimen of so-called pure y8, containing 52-12 p.c. 

 copper, 17 • 85 p.c. zinc, enclosed in a glass tube, was heated in sulphur 

 vapour at 445° C. for six weeks. Microscopic examination did not in- 

 dicate that any appreciable progress towards coalescence of a and y 

 particles had taken place. An alloy consisting of (3 with a little a, and 

 an alloy consisting of (3 with a little y, were then annealed in a similar 

 manner. After sufficiently lengthy annealing, it was found that the 

 )8 constituent had been replaced by massive a and y in l)oth cases. The 

 author concludes that below 1:70" C. the so-called /3 constituent is to be 

 regarded as an intimate eutectoid mixture of a and y particles ; the 

 structural stability of this complex is so great that coalescence only occurs 

 on annealing when either a or y is present in excess. 



* Journ. lud. Eng. Chem., iii. (1911) pp. 368-72, through Journ. Soc. Cheni' 

 Ind., XXX. (1911) pp. 811-12. 



+ Engineering, xcii. (1911) p. 864 (1 fig.). 

 t Metallurgie, viii. (1911) pp. 137-8 (2 figs.). 

 § Metallurgie, viii. (1911) pp. 731-6 (16 figs.). 

 I Journ. Inst. Metals, vii. (1912) pp. 70-104 (24 figs.). 



