RECENT SCIENCE. 623 



Moissan's method is based upon the capacity of iron of absorb- 

 ing carbon at a high temperature and of giving it back in the 

 shape of grains and crystals while the iron mass is cooling. 

 When iron has been saturated with carbon at a temperature of 

 -about 2,000° Fahr., a mixture of amorphous carbon and graphite 

 is discovered in the iron mass. At higher temperatures the fused 

 iron dissolves more and more carbon, and the cast iron of our 

 blasting furnaces, after having been heated to about 3,000° and 

 slowly cooled down, contains, as known, an abundance of graphite 

 ■crystals. It was thus natural to see whether a still higher tem- 

 perature, and cooling under high pressure, might not give the 

 still denser form of carbon — that is, the diamonds. 



In order to thoroughly saturate iron with carbon at a high 

 temperature, and to cool it under a high pressure, Moissan re- 

 sorted to a very simple and effective means. He took a hollow 

 ■cylinder of soft iron, filled it with some purified sugar charcoal, 

 and corked the cylinder with an iron screw. Then about half a 

 pound of soft iron was molten in a crucible in Moissan's new elec- 

 tric furnace, which readily gives a temperature of about 3,000° 

 C. (5,400° Fahr.), and the cylinder was plunged into the molten 

 metal; iron was thus thoroughly saturated with carbon. The 

 crucible was then taken out of the furnace and plunged into a 

 pail of cold water until the surface of the iron mass was cooled to 

 a, dull red temperature, whereupon it was taken out and left to 

 •cool in the air. This was the ingenious means of obtaining a 

 high pressure. It is known that water when it becomes ice 

 increases in volume, and that if it freezes in a strong shell the 

 interior pressure of the crystallizing water often bursts the shell ; 

 out if it can not burst the shell it necessarily solidifies under an 

 immense pressure, due to the molecular forces. The same was 

 ■done by Moissan with the liquid iron, which also has the property 

 of increasing in volume while it solidifies. An outer solid crust 

 having been formed by a sudden immersion into cold water, the 

 •crust prevents the further expansion of the iron mass, which is 

 thus bound to solidify under an immense pressure, like the water 

 in the shell. 



The next step was to separate the iron from the carbon crystals 

 which it might contain. This was done by dissolving the iron in 

 hydrochloric acid, and three different varieties of carbon crystals 

 •(which are not attacked by the acid) were received as a residue. 

 Some graphite, some chestnut-colored, curved needles of carbon, 

 and diamond dust could be seen ; and they were separated from 

 each other by several complex operations indicated by Berthelot 

 in one of his previous works. A few grains of diamond dust were 

 finally obtained — most of them belonging to the carbonado va- 

 riety, while a few of them proved to be real diamonds ; they were 



