Reports and Proceedings — British Association. 477 



Heycoch and Neville's Worlc on Alloys. 



I must next refer briefly to another remarkable series of researcbe& 

 which have recently been published. 



The laws which govern the solutions of metals in metals, that is 

 to say alloys, appear to be the same as those which prevail in the 

 case of other solutions ; it is in alloys that the nature of eutectic 

 mixtures has been most fully studied ; and the phase-rule and 

 Eoozeboom's deductions from it have been applied with signal 

 success to their investigation. A new impulse has been given to the 

 subject by the work of Heycock and Neville, which is summarised 

 in their Bakerian lecture delivered last year upon the copper-tin 

 series of alloys. They have studied the changes which occur during 

 the cooling of an alloy by taking small ingots of the cooling metal 

 and chilling them at certain temperatures ; this arrests the gradual 

 process of cooling, and causes all that is liquid at the moment of 

 chilling to become suddenly solid ; it is then possible by polishing 

 and etching the ingot to show the solid crystals set in the congealed 

 ground-mass and to study their nature. They have been able ta 

 interpret their results by means of Eoozeboom's remarkable work 

 on the solidification of mixed crystals published in 1899. For our 

 present purpose it is sufficient to consider these results as applied 

 only to alloys. If a diagram be constructed with the temperatures 

 for ordinates and constitution for abscissEe, Roozeboom has shown 

 that two curves may be drawn. The first is the freezing-point 

 curve, or liqmdus, giving the temperatures at which an alloy of any 

 composition begins to solidify : this is a broken curve, and each 

 section of it represents the temperature of equilibrium between the 

 liquid and a different solid alloy ; the breaks represent the tempera- 

 tures and constitution of the liquid at which one solid ceases to be 

 produced and another begins. The curve is, of course, far more 

 complicated than the simple V of Meyerhoffer, since that represents 

 the cooling of a mixture whose constituents do not form compounds 

 or isomorphous mixtui-es, whereas the alloys do both. In this 

 respect the alloys resemble a silicate magma which is crystallising 

 as a rock-mass ; indeed, it will be remembered that Mendeleef insists 

 upon the general similarity of silicon compounds to metallic alloys. 



The second curve of Eoozeboom is the melting-point curve, or 

 solidus, representing the temperatures at which an alloy of given 

 composition becomes completely solid. Points above the liquidus 

 represent the condition of alloys which are completely liquid ; points 

 below the solidus that of alloys which are completely solid ; points 

 between the two that of cooling alloys which are only partially solid ; 

 and the curves themselves show which solid compounds can be in 

 equilibrium with the liquid and with each other at any temperature. 



The cooling-curves of Eoberts-Austen and Stansfield had shown 

 that considerable evolutions of heat may occur in cooling alloys far 

 below the temperature of solidification, indicating that changes are 

 going on in the solid as well as in the liquid condition. Heycock 

 and Neville carry their investigations below the temperature of 

 complete solidification and study these changes also. 



