ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 775 



illumination. Another advantage of rny plan is, the larger colonies are 

 left behind in their natural habitats, and the danger of extermination 

 is reduced to a minimum. My method, as detailed above, I have found 

 equally successful for PlumaMla, Lophopus, Alcyonella, FredericeUa, 

 Cristatella, etc. Of course, in the case of such voracious creatures, ample 

 food must be supplied, and, from my own extended observations, I 

 conclude that this is largely vegetable. Where practicable, I invariably 

 keep the specimens supplied with water from the original habitat ; but 

 when that could not be done, I have found tap-water, with the addition 

 of some clear river-water, to answer very well. Experiments with tap- 

 water alone have not been so successful." 



Metallography, etc. 



Etching of High Carbon Steel.* — E. H. Saniter having failed to 

 obtain good etching of high carbon steels, especially in the tempered 

 condition, with iodine, 2 p.c. nitric acid or picric acid, tried Sauveur's 

 method of dipping in strong nitric acid (sp. gr. 1 ■ 42) and washing at 

 the tap. This gave better results, but several treatments were required 

 to obtain the desired etching. He then tried dipping the specimen in 

 absolute alcohol, followed by strong nitric acid and washing at the tap. 

 This gave a good etching with only one treatment. The specimen 

 should be held in a pair of forceps and moved about rapidly in the acid. 

 Fresh acid must be used for each etching. 



Metallography of Iron and Steel.f — R. A. Hadfield, in his 

 Presidential Address to the Iron and Steel Institute, regrets the tendency 

 to multiply the names of micro-constituents, and suggests the terms 

 " martensitic structure," " sorbitic structure," as being less liable to 

 misconstruction than the terms " martensite," " sorbite." The marked 

 differences of opinion as to the meaning of the currently accepted 

 designations of the constituents of steel should lead to caution in their 

 use. The address deals with a very wide range of topics connected with 

 the metallurgy of iron and steel. 



Experiments relating to the Effect on Mechanical and other 

 Properties of Iron and its Alloys produced by Liquid Air Tem- 

 peratures.:): — R. A. Hadfield, after giving a resume of previous 

 investigations into the properties of metals at low temperatures, describes 

 his methods of mechanically testing at the temperature of liquid air, and 

 gives the results of mechanical and electrical tests, some 1600 in number, 

 carried out on an extensive series of alloys. At — 182° C, commercially 

 pure iron, which is highly ductile at the ordinary temperature, becomes 

 brittle and has a much greater tensile strength. Great increase in 

 tenacity and decrease in ductility also result when carbon steels (0 ' 1 p.c. 

 to 1-5 p.c. carbon) are cooled to —182° C. Brinell hardness tests con- 

 firm these conclusions. Nickel on the contrary improves both in tenacity 



* Iron and Steel Mag., x. (1905) p. 156. 



t Journ. Iron and Steel Inst., lxvii. (1905) pp. 85-7. 



t Tom. cit, pp. 147-219 (14 figs., 37 diagrams); Discussion, pp. 220-55. 



