1892.] 



on Metals at High Temperatures. 



513 



In the next experiment, Fig. 6, a bar of steel, J incli in section 

 and 18 inches long, was heated to bright redness and fixed firmly 

 at one end ; a weight of about two pounds is rapidly hung to the 

 free end, a light pointer is added to magnify the motion of the bar, 

 and the thermo-junction is rapidly introduced into a small hole 

 drilled in what is arranged to be the hottest part of the bar. The 

 bar is not softest at a red heat ; it remains perfectly rigid until it 

 has cooled down to dull redness, and the temperature, as measured 

 by the spot of light from the galvanometer, shows that " recalescence " 

 has occurred. At that moment of molecular weakness in the bar, 

 the weight has power to bend it, and the pointer fulls. By such 



experiments the exact temperature at which the metal becomes weak, 

 in difterent varieties of steel, can readily be determined. 



(2) Evidence will now be given in support of the second case it 

 vs^as proposed to treat, and it will be shown that at high temperatures 

 the atoms of metals may truly combine with each other ; in fact, taking 

 gold as a basis for the experiments, compounds may be formed which 

 would, had they been known centuries ago, have strangely affected the 

 history of science. When the alchemists subjected the metals to high 

 temperatures, their efforts were mainly directed to the discovery of 

 some substance that would either change base metals to the colour of 

 gold, or would give them the brilliancy of silver. The medi£eval 

 chemists believed that there were two distinct substances that would 

 effect this, " one for the white " and another " for the red." Many of 

 their writings might be quoted in support of this view, but a reference 

 to Geber, who wrote in the eighth century, will be sufficient. He 

 pointed out that the transmuting agent " has a tincture of itself so 

 clear and splendid, white or red, clean and incombustible, stable and 

 fixed, that hre cannot prevail against it ; . . . and a property of the 

 medicine is to give a splendid colour, white or intensely citrine," to 

 metals to which it is added. 



