DIAMONDS. 227 



Professor Dewar Las made a calculation as to the critical pressure of 

 carbon, that is the lowest pressure at which carbon can be got to assume 

 the liquid state at its critical temperature, that is, the highest tempera- 

 ture at which liquefaction is possible. He starts from the vaporizing 

 or boiling point of carbon, which, from the experiments of Violle and 

 others on the electric arc, is about 3,600° C, or 3,874° Absolute. The 

 critical point of a substance on the average is 1.5 times its absolute 

 boiling point. Therefore the critical point of carbon is 5,81]° Ab., or, 

 say, 5,800° Ab. But the absolute critical temperature divided by the 

 critical pressure is for elements never less than 2.5. Then — 



5,800° A. OK Tin 5,800° A. o qoh + i. 



-1-— = 2.5 or PCr = ' ^ ^ — , or 2,320 atmospheres. 



POr 2.5 



The result is that the critical pressure of carbon is about 2,300 atmos- 

 pheres or, say, 15 tons on the square inch. The highest critical pres- 

 sure recorded is that of water, amounting to 195 atmospheres, and the 

 lowest that of hydrogen, about 20 atmospheres. In other words, the 

 critical pressure of water is ten times that of hydrogen, and the criti- 

 cal pressure of carbon is ten times that of water. 



Now, 15 tons on the square inch is not a difflcult pressure to obtain 

 in a closed vessel. In their researches on the gases from fired gun- 

 powder and cordite. Sir Frederick Abel and Sir Andrew Noble obtained 

 in closed steel cylinders i)ressures as great as 95 tons to the square 

 inch, and temperatures as high as 4,000° C. Here, then, if the obser- 

 vations are correot, we have sufficient temperature and enough pres- 

 sure to liquefy carbon ; and if the temperature could only be allowed 

 to act for a sufficient time on the carbon there is little doubt that the 

 artificial formation of diamonds would soon pass from the microscopic 

 stage to a scale more likely to satisfy the requirements of science, 

 industry, and personal decoration. 



ARTIFICIAL MANUFACTURE OF THE DIAMOND. 



I will now proceed to manufacture a diamond before your eyes. Don't 

 think I yet have a talisman that will make me rich beyond the dreams 

 of avarice. Hitherto the results have been very microscopic, and are 

 chiefly of scientific interest in showing us nature's workshop, and how 

 we may ultimately hope to vie with her in the manufacture of diamonds. 

 Unfortunately, the operations of separating the diamond from the iron 

 and other bodies with which it is associated are somewhat prolonged, 

 nearly a fortnight being required to detach it from the iron, graphite, 

 and other matters in Avhich it is embedded. I can, however, show the 

 different stages of the operations, and project on the screen diamonds 

 made in this manner. 



In Paris, recently, I saw the operation carried out by M, Moissan, 

 the discoverer of this method of making carbon separate out in the 

 transparent crystalline form, and I can show you the operations 



