ARTIFICIAL PRECIOUS STONES—HEATON, 223 
Taking these two points in conjunction, and confining our atten- 
tion for the moment to the transparent stones as summarized in 
Table III, the diamond appears to offer the most promising field for 
attack and corundum comes next, and we find that the main attempts 
at artificial production center round these species. From the point 
of view of composition alone, quartz is the most simple, but it is so 
common in nature as to render its artificial production scarcely worth 
while. The aluminate group offers some attraction, but the artificial 
production of crystalline silicates on a large scale is a very difficult 
problem, and, with the exception of the emerald, the stones com- 
prised in this group are so freely distributed in nature as to render 
their artificial production a matter of academic rather than industrial 
interest. 
It is unnecessary to discuss at any length the artificial production 
of the diamond'—the problem has been attacked by numerous 
scientists, and was solved by Moissan some years ago. Some 15 
years ago, on the occasion of a visit to Paris, I had the privilege of 
witnessing the production of his diamonds, prepared, as all the 
world knows, by saturating iron with carbon at the temperature 
of the electric arc and plunging the molten mass into cold water. 
The mass of iron is then dissolved in acid and the residue subjected 
to a laborious process of extraction, the diamonds being picked out 
by aid of the microscope. The largest diamond that has been pro- 
duced in this way is barely visible to the naked eye, however, and 
when I say that the problem of their production has been solved, 
I mean from the scientific point of view. 
The artificial production of the diamond is, in fact, far more com- 
plicated than it appears at first sight. If it were only a matter of 
obtaining the necessary high temperature to fuse the carbon to obtain 
it in the crystalline condition it would be simple—such high tempera- 
tures are readily obtained nowadays by means of the electric furnace 
and the oxy-acetylene flame—but carbon is one of those substances 
which pass direct from the solid to the gaseous state under ordinary 
atmospheric conditions, and only assumes the liquid condition 
under enormous pressure. The combination of high temperature 
and enormous pressure can be obtained momentarily by Moissan’s 
ingenious process, but to obtain crystals of any size it is necessary to 
conduct the operation on a very large scale and to maintain the com- 
bined temperature and pressure for a sufficient length of time to 
allow the liquid carbon to separate out from its matrix; moreover, 
the entire operation must be conducted out of contact with air, for 
carbon rapidly combines with oxygen at high temperatures. 
1A complete account is given in ‘‘Diamonds,” by Sir William Crookes (Harper’s Library of Living 
Thought). 
