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adhering so tightly that it was found impossible to detach 
them entire. 
One other experiment is worthy of notice before proceeding 
to the only one which had any practical result ; it is that of M. 
de Senarmont, who obtained similar microscopic crystals by 
exposing hydrate of alumina, or alumina combined with water, 
to a great heat, which caused the water to evaporate, and left 
the crystals at the bottom of the glass tubes in which the 
experiment was conducted. 
The perseverance of M. Gaudin, who appears never to have 
abandoned the idea of manufacturing precious stones, enabled 
him, in 1857, to present to the Academy of Sciences several 
white sapphires produced by a very simple process, and of 
sufficient size to be used as jewels in watches. 
The following is the mode of procedure by which M. Gaudin 
succeeded in producing these crystals : — ■ 
In a crucible lined with animal charcoal are placed equal 
parts of alum and sulphate of potash, previously calcined to 
expel the water. With this mixture the crucible is half filled ; 
it is then filled up to' the top with animal charcoal, the lid is 
put on and cemented in its place with clay, and it is then 
exposed in a furnace, and kept at a white heat for a quarter of 
an hour. The heat and the reducing power of the charcoal 
cause the formation of sulphuret of potassium, which fuses 
and dissolves the alumina; the continued action of the heat 
partly evaporates this sulphuret of potassium, and the alumina 
separates in the form of little crystals. On opening the crucible, 
a black mass, sparkling with brilliant points, is found in it, which 
consists of sulphuret of potassium mixed with crystals of alumina. 
This mass is afterwards placed in diluted nitro-hydrochloric 
acid, which dissolves the sulphuret, and lets fall the crystals of 
alumina to the bottom of the vessel, where they appear as a 
coarse powder, and, seen through a microscope, have an exact 
resemblance in form to the natural precious stones. By using a 
larger crucible, and exposing it to the action of the fire for a 
longer period, M. Gaudin produced crystals of much greater 
dimensions, which, upon examination, proved to be true white 
sapphires, and were even superior in hardness to the rubies 
ordinarily used for the jewelling of watches. He endeavoured 
to produce coloured crystals by the addition of metallic oxides, 
but found that these were invariably reduced into metals 
by the action of the charcoal. The successful result of this 
experiment encourages us to hope that at a future period 
M. Gaudin, or some one else possessed of his indomitable per- 
severance, may discover some substance capable of dissolving 
carbon in a similar manner to that in which sulphuret of 
potassium has been found to dissolve alumina, by which the 
