262 THE POPULAR SCIENCE MONTHLY. 



dissolves in a gaseous solvent, from which solution of carbon crystals 

 are then obtained, just as table-salt is produced by the evaporation of 

 brine, and these crystals are diamond. 



The temperature at which the dissociation of the hydrocarbon" is 

 effected must be very high, and the pressure enormous, so that the 

 great difficulty of the process lies in the construction of an inclosing 

 vessel strong enough to withstand the combination of heat and disrup- 

 tive force. Coiled tubes of wrought iron, of half an inch bore and 

 four inches external diameter, have been torn open in nine cases out 

 of ten. 



The mineralogical tests which demonstrate the genuineness of dia- 

 mond are as follows : It must scratch topaz and sapphire, its angles 

 must be those of a regular octahedron, it must burn without leaving 

 any residue, and it must exert little or no action on polarized light. 

 Professor Maskelyne, of the British Museum, has already stated in the 

 "Times "that Mr. Hannay's crystals satisfy all these tests. They 

 score topaz and sapphire easily and deeply ; the angle of their cleav- 

 age-faces, which could not be measured with great accuracy on ac- 

 count of the minuteness of the gems, is 70 29', while that of the dia- 

 mond is 70 30'. Particles ignited on platinum glow and disappear 

 exactly as the gem would do, and they are very nearly inert in polar- 

 ized light. 



It is not long since science rejected the claims of another Glasgow 

 investigator to the artificial production of crystalline carbon, and it is 

 somewhat singular that Mr. Hannay's successful solution of this great 

 chemical problem should have followed so quickly upon Mr. McTear's 

 failure. 



That the diamonds in this case are real there is now no question ; 

 and it is quite possible that, just as experience has taught chemists 

 how to produce large and perfect crystals from solutions which under 

 ordinary treatment yield only small and imperfect specimens, so Mr. 

 Hannay may by and by succeed in making diamonds as big as the 

 Koh-i-noor or the Regent. 



We learn, however, from the investigator's own statement, that up 

 to the present time it has cost him five pounds to produce five shil- 

 lings' worth of diamond ; but, even if the world of fashion is destined 

 to deplore the degradation of its cherished gem, we may be sure that, 

 long after some new toy has satisfied society for its loss, the crystalli- 

 zation of carbon will possess for the greater world of science the same 

 kind of interest as clings around the discovery of oxygen by Priestley, 

 or the demonstration of magneto-electricity by Michael Faraday. 

 Belgravia. 



