ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 627 



one solid solution, were found to be the most constant in their thermo- 

 electric behaviour. 



Micro-chemistry of Corrosion : u-/3 Copper-zinc Alloys.* — 8. Whyte 

 has applied the methods previously described to an a-fi alloy containing 

 60 '8 p.c. copper and 39*2 p.c. zinc, to three alloys of similar com- 

 position but having 1 p.c. zinc replaced by 1 p.c. of iron, 1 p.c. of lead, 

 and 1 p.c. of tin respectively, and to a pure a and a pure fi alloy. 

 Corrosion in sodium chloride solution was stimulated by an electric 

 current, and the effects were determined by microscopical and chemical 

 methods, ft corroded more rapidly than a, and corrosion proceeded 

 in all cases by dezincification. In alloys containing both a and /?, the 

 layer of copper formed was thicker over the /? constituent than over a. 



Appliances for Metallographic Research.f — W. Rosenhain de- 

 scribes a levelling device for metallographic specimens. A small, low- 

 power telescope is rigidly fixed in a vertical position, with the eye- 

 piece uppermost. A plane glass reflector, set at 45° to the axis, is fixed 

 in the tube a little below the eye-piece. This reflects downwards the 

 light admitted horizontally through a small hole in a plate at the end of 

 a short side tube. A few inches below the objective a glass plate, 

 silvered on its lower face, is adjusted accurately at right angles to the 

 axis of the telescope, by bringing the image of the small hole on to 

 the cross wires of the eye-piece. The specimen, mounted on a slip by 

 means of plasticine, is placed on the glass plate and acts as the re- 

 flector ; its level is adjusted until the image of the small hole again 

 falls on the cross wires. The polished face of the specimen is then 

 parallel to the lower surface of the slip on which it is mounted. The 

 adjustment can be made in a few seconds. Some appliances for use in 

 taking thermal curves are also described. 



Etching Reagents. J— 0. F. Hudson discusses etching reagents 

 generally, and gives a detailed description of the action of all the re- 

 agents in common use, and of many which have been used for special 

 purposes. In an etched surface of a pure metal the appearance of 

 the crystal boundaries as black lines may be due in part to the more 

 rapid solution of the metal at the boundaries. Etching usually produces 

 some roughening of the surface of each crystal, and staining due to a 

 film of oxide. When two or more constituents are present, they are 

 commonly stained to a markedly different extent, and such differences 

 are employed to distinguish the constituents. The amorphous surface 

 film produced by the polishiug of a specimen does not as a rule seriously 

 interfere with the effects produced by etching, but its presence should 

 not be overlooked. 



Electrolytic etching, polish attack —a method which the author believes 

 is ik it adopted as widely as it should be — and heat-tinting are de- 

 scribed. A list of metals and alloys, with the etching reagents suitable 

 for each, is given. 



* Journ. Inst. Metals, xiii. (1915, 1) pp. 80-99 (11 figs.). 

 t Journ. Inst. Metals, xiii. (1915, 1) pp. 1G0-92 (13 figs.). 

 X Journ. Inst. Metals, xiii. (1915, 1) pp. 193-221 (2 figs.). 



