ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1-1. 



tests. The thickness of carburised layer obtained by case-hardening at 

 different temperatures for various lengths of time was determined for 

 steels containing as the alloy element, nickel, titanium, silicon, man- 

 ganese, chromium, tungsten, and molybdenum. The results of much 

 other experimental work are given, but it is difficult to ascertain whether 

 the numerous and varied statements made by the author are conclusions 

 drawn from his own work or are based upon other published investigations. 



Special Ternary Steels. *— A. M. Portevin has carried out shearing 

 tests by the Fremont method, and tensile tests, on a large number of 

 alloys of iron and carbon with a third element. The electrical resistance 

 of the steels was also determined, and the relations between electrical 

 resistance, chemical composition, micro-structure and heat- treatment 

 were investigated. ' The steels used contained as third element man- 

 ganese, nickel, chromium, tungsten, vanadium, aluminium, silicon, 

 molybdenum, titanium, tantalum and boron, and were the steels of 

 which other properties had been determined by Guillet. It does not 

 appear possible to express the relation between tensile and shearing pro- 

 perties by any general formula). For a given series of alloys, the curve 

 showing the relation between proportion of third element and electrical 

 resistance is made up, as a rule, of several rectilinear portions, and the 

 inflections in the curve correspond 'with changes in micro-structure. 

 The thermal critical points of a number of vanadium and titanium 

 steels were determined. A bibliography is appended. 



Iron-carbon Diagram. — F. Wustf gives an historical account of the 

 development of the equilibrium diagram of the iron-carbon system, and 

 states the experimental evidence on which he founds the following con- 

 clusions. Carbon is not dissolved in molten iron as elementary carbon, 

 but as carbide of iron. " Kish " is formed by the decomposition of the 

 carbide which crystallises from the fluid solution. The solidification of 

 iron-carbon alloys does not take place according to the equilibrium curves, 

 which apply only to the stable system. Graphite is formed by the decom- 

 position of separated carbide. Elements present other than iron and 

 carbon have both a direct and an indirect influence on graphite-forma- 

 tions : (a) direct, in that they enter into the composition of the carbide, 

 and either increase its rate of decomposition (silicon, nickel, aluminium) 

 or decrease it (manganese, chromium, tungsten) ; (b) indirect, in that 

 the solubility curve of iron carbide in solid or liquid iron is displaced, 

 and the quantity of separated free carbide is correspondingly greater or 

 smaller. The carbide is decomposed in solid alloys by the action of heat. 

 The influence of foreign elements on the temperature at which temper 

 carbon is set free has the same explanation as in the case of graphite 

 formation. 



P. GoerensJ deals very fully with ternary systems consisting of iron, 

 carbon, and a third element. As an example to illustrate methods of 

 investigating and representing ternary equilibriums, the lead-tin-bismuth 

 system is selected. A model showing the diagram in solid form may be 

 constructed from sheets of transparent celluloid, each representing a 

 section through the diagram, erected perpendicular to a triangular base 



* Iron and Steel Insfc., Carnegie Scholarship Memoirs, i. pp. 230-364 (67 figs.). 

 t Metallurgie, vi. (1909) pp 512-31 (19 figs.). 

 X Tom. cit., pp. 531-6, 537-50 (46 figs ). 



