RECORDS OF MEETINGS. 705 



By moderate reheating of chilled and hardened steel a partial change 

 from the unstable hard condition may be effected ; a partial recovery 

 of the condition and proportion of constituents normal to soft or slowly 

 cooled steel. This is tempering, and allows just such a degree of hard- 

 ness to be retained as is needed, while the brittleness is diminished. 



A curious physical fact recently found by Prof. Carl Barus is that 

 during the lapse of a sufficient time all hardened steel will anneal or 

 soften itself automatically, even at ordinary temperatures, but that the 

 change will be accelerated as we raise the temperature. Fortunately 

 the period for this self annealing in the cold is long ; but it follows 

 that if we were to dig up steel tools which had been hardened say two 

 or three thousand years ago, we ought to find them much softer than 

 they were originally. 



Our scientific knowledge of steel is, of course, not yet complete. 

 Steels with new constituents and more valuable properties are con- 

 tinually being made. For example may be mentioned the so-called 

 air hardening or high speed steels which have added so enormously 

 to the productiveness of machinery and labor in the working of iron 

 and steel itself, and metals generally. Iron and steel production 

 goes on at a rapid rate of increase. Our consumption per capita 

 per annum is already several hundred pounds, and the amount is larger, 

 if I mistake not, in the United States than in any other country. 

 Perhaps we waste more. 



The first Academy paper which I have reread describes that method 

 of steel making known as the cementation process. Even until very 

 recently this was the method almost universally relied upon for the 

 production of high grades of tool steel, but within a decade or so the 

 art of refining steel has reached such an advanced stage that great 

 quantities of fine steel are made in what are known as basic open 

 hearth furnaces. Lastly, the advent of the electric arc furnace, some 

 of them dealing with charges of 30,000 pounds or more at a time, has 

 rendered possible refining at very high temperatures, far beyond those 

 of ordinary combustion furnaces. The more perfect control and ex- 

 clusion of deleterious gases allows separation of impurities and control 

 of composition so as to ensure the product having the qualities desired. 

 In these furnaces electric arcs are maintained on a scale many thousands 

 of times greater than the arcs used in lighting our streets. The enor- 

 mous output of heat and light is shut up within the furnace walls, or 

 it would be insupportable, insufferable. Its energy goes to raise the 

 temperature of the molten steel bath, and the energy itself may be 

 drawn firom a water power. 

 As in the case of steel making, many an art has been discovered 



VOL. XLVI. — 45. 



