8 MODERN SCIENCE READER 



in the least. The pressure which I have brought to bear 

 in this experiment has been equal to 170 tons per square 

 inch of diamond. 



The only serious rival of the diamond in hardness is the 

 metal tantalum. In an attempt to bore a hole through a 

 plate of this metal, a diamond drill was used revolving at 

 the rate of 5,000 revolutions per minute. This whirling 

 force was continued ceaselessly for three days and nights, 

 when it was found that only a small point, one fourth of a 

 millimeter deep, had been drilled, and it was a moot point 

 which had suffered most damage, the diamond or the 

 tantalum. 



After exposure for some time to the sun, many diamonds 

 glow in a dark room. One beautiful green diamond in my 

 collection, when phosphorescing in a vacuum, gives almost 

 as much light as a candle, and you can easily read by its 

 rays. But the time has hardly come when we can use dia- 

 monds as domestic illuminants! Mrs. Kunz, wife of the 

 well-known New York mineralogist, possesses perhaps the 

 most remarkable of all phosphorescing diamonds. This 

 prodigy diamond will phosphoresce in the dark for some 

 minutes after being exposed to a small pocket electric light, 

 and if rubbed on a piece of cloth a long streak of phos- 

 phorescence appears. 



For the manufacture of a diamond, the first necessity is 

 to select pure iron free from sulphur, silicon, phosphorus, 

 and so forth and to pack it in a carbon crucible with pure 

 charcoal from sugar. The crucible is then put into the 

 body of the electric furnace, and a powerful arc formed 

 close above it between carbon poles, utilizing a current of 

 700 amperes at 40 volts pressure. The iron rapidly melts 

 and saturates itself with carbon. After a few minutes' 

 heating to a temperature above 4,000 C. a temperature 

 at which the iron melts like wax and volatilizes in clouds 

 the current is stopped, and the dazzling fiery crucible is 

 plunged beneath the surface of cold water, where it is held 

 till it sinks below a red heat. 



