GOLD IN SCIENCE AND IN INDUSTRY. 225 



enerofiziiify influence of heat. This temporarv abeyance of the more 

 active properties of matter is strikingly ilhistratod l)y the early obser- 

 vations of Sir James Dewar at the boilino- point of liquid air, and 

 more recently at that of liquid hydrogen. At the latter temperature 

 even chemical affinity becomes latent. In metals it was found that 

 the changes in their physical properties brought about by these low 

 temperatures are not permanent, but only persist so long as the low 

 temperature is maintained. During the past year Mr. R. A. Hadfield 

 has supplemented these earlier results by making a very coni]:)lete 

 series of observations on the elfect of cooling on the mechanical prop- 

 erties of iron and its alloys. The tenacity and hardness of the pure 

 metal and its alloys at the ordinary tempmerature and at — 182° have 

 i)een compared, and it has been found that these qualities are invaria- 

 bly enhanced at the lower temperature, but that they return exactly to 

 Iheir former value at the ordinary temperature. By the mere abstrac- 

 tion of heat between the temperatures of 18° and — 182° the tensile 

 strength of pure metals is raised 50 to 100 per cent. In pure iron the 

 increase is from 23 tons per square inch at 18° C. to 52 tons at 

 — 182° ; in gold from 15 • 1 tons to 22 • 4 tons ; and in copper from 10*5 

 tons to 26 '4. This increase is not, I think, due to the closer approxi- 

 mation of the molecules, for the coefficient of expansicm of most metals 

 below 0° is extremely small. Neither is it due to permanent changes 

 of molecular arrangement or aggregation, for Mr. Ha'Ifield has 

 ol)tained a perfectly smooth and regidar cooling curve for ii-on 

 between 18° and — -182°, and there appears to be no indication of the 

 existence of any critical point between these temperatures. Further, 

 the complete restoration of the original tenacity on the return to the 

 higher temperature shows that no permanent or irreversible change 

 has occurred durino- cooling. Evervthing therefore indicates that the 



to & .to 



increase of tenacity which occurs degree by degree as heat is removed 

 is due to the reduction of the repulsive force of molecular vibration, 

 so that the primary cohesive force can assert itself more and more 

 completely as the absolute zero is approached. 



The metals experimented with by ]Mr. Hadfield were all in the 

 annealed or crystalline condition, so that the molecules must have 

 exerted their mutual attractions along the directed axes proper to this 

 state. It is to be expected that similar experiments with the metals in 

 the amorphous state may throw light on the question whether and to 

 what extent the crystalline state depends on a dynamic equilibi-ium 

 between the forces of cohesion and repulsion, or whether a directed 

 cohesion exists fully developed in the molecules at the absolute zero."^ 



a Since the above was written a series of observations has been made on the 

 influence of low tenii)eratiu'e on the tenacity of ]mre metals in the amoi'iilions 

 condition. These observations will form the subject of a separate communication 

 to the chemical section. 



