226 DIAMONDS. 



The diamond is remarkable in another respect. It is extremely trans- 

 parent to the E(intgen rays, whereas highly refracting glass, used in 

 imitation diamonds, is almost perfectly opaque to the rays. I exposed 

 over a photographic plate to the X-rays for a few seconds the large 

 Delhi diamond, of a fine pink color, weighing 31^ carats, a black dia- 

 mond weighing 23 carats, together with an imitation in glass of the 

 pink diamond lent me by Mr. Streeter; also a flat triangular crystal of 

 diamond of pure water, and a piece of glass of the same shape and size. 

 On development, the imj)ression where the diamond obscured the rays 

 was found to be strong, showing that most rays passed through, while 

 the glass was practically opaque. By this means imitation diamonds 

 and some other false gems can readily be detected and distinguished 

 from the true gems. It would take a good observer to distinguish my 

 pure triangular diamond from the adjacent glass imitation. 



GENESIS OF THE DIAMOND. 



Speculations as to the probable origin of the diamond have been 

 greatly forwarded by patient research, and particularly by improved 

 means of obtaining high temperatures. Thanks to the success of 

 Professor Moissan, whose name will always be associated with the 

 artificial production of diamonds, we are able to day to manufacture 

 diamonds in our laboratories — minutely microscopic, it is true — all the 

 same veritable diamonds, with crystalline form and api^earance, color, 

 hardness, and action on light the same as the natural gem. 



Until recent years carbon was considered absolutely nonvolatile and 

 infusible; but the enormous temperatures at the disposal of experi- 

 mentalists — by the introduction of electricity— show that instead of 

 breaking rules, carbon obeys the same laws that govern other bodies. 

 It volatilizes at the ordinary pressure at a temperature of about 3,600° 

 C, and passes from the solid to the gaseous state without liquefying. 

 It has been found that other bodies which volatilize without liquefy- 

 ing at the ordinary pressure will easily liquefy if pressure is added to 

 temperature. Thus, arsenic liquefies under the action of heat if the 

 pressure is increased; it naturally follows that if along with the requi- 

 site temperature sufficient pressure is applied, liquefaction of carbon 

 will be likely to take place, when on cooling it will crystallize. But 

 carbon at high temperatures is a most energetic chemical agent, and if 

 it can get hold of oxygen from the atmosphere or any compound con- 

 taining it, it will oxidize and fly off in the form of carbonic acid. Heat 

 and pressure, therefore, are of no avail unless the carbon can be kept 

 inert. 



It has long been known that iron when melted dissolves carbon, and 

 on cooling liberates it in the form of graphite. Moissan discovered 

 that several other metals have similar properties, especially silver; but 

 iron is the best solvent for carbon. The quantity of carbon entering 

 into solution increases with the temperature, and on cooling in ordinary 

 circumstances it is largely deposited as crystalline graphite. 



