PRESIDENT’S ADDRESS. 35 
It is found that at the very low temperature of liquid 
air that chemical action almost disappears, and that electric 
resistance also decreases, and at such rate that the curves 
indicate the total disappearance of the latter at what is 
termed the absolute zero, 7.e.,—273° C. The tensile strength 
of many metals is much increased. 
Certain substances also lose their colour, e.g., flowers of 
sulphur becomes white at —50° C, and photographic plates 
lose their sensitiveness. 
ARTIFICIAL DIAMONDS AND OTHER GEMS. 
The preparation of artificial gems has long had an attrac- 
tion for many chemists, and the preparation of artificial 
diamonds (imitation diamonds are easily made out of glass 
or paste) is now an accomplished fact, but at present they 
have only been made of a very small size, and are value- 
less as gems. It may, however, be possible to make larger 
ones in course of time, but at present they have all been of 
microscopic size. 
But as diamond dust is very expensive, the smaller gems 
will have a considerable market value if they can be made 
cheaply enough. 
It would take too long to describe all the different methods 
employed to prepare artificial diamonds since the first 
attempts were made by Wilson in 1850. Hannay, in 1880, 
claimed to have made diamonds by submitting hydro- 
carbons at a very great heat, in strong steel cylinders, to 
the action of metals like lithium and magnesium. 
About the same time Mactear also states that he had 
obtained them ; clear, transparent, and with the form and 
refractive power of the natural diamond, but small in size. 
Prof. Moissan, in 18935, prepared artificial diamonds by 
dissolving pure charcoal made from sugar in molten iron 
in the electric furnace, and then suddenly cooling the 
carburised iron in lead; the iron and impurities were 
removed by acids, and minute crystals of diamond left. 
