SAPPHIRES OBTAINED BY A CHYMICAL PROCESS. 345 
plied to plants in fields as well as in gardens, and since I had 
proved, moreover, that well-rotted dung did not contain 
nitre, and that none was produced by its mixture with the 
earth. Neither could this cause be attributed to the pre- 
sence of animals, since they are ordinarily excluded from 
gardens, and that urine is not thrown into them ; it could 
only reside, therefore, in the artificial watering which cannot 
be given to plants in fields, but which garden plants received. 
Herein, appeared to me, the cause of the nitrification of 
these plants ; so that if I have correctly observed these 
facts, if I have not deceived myself in the conclusions which 
I have drawn from them, if I have proved that nitric acid is 
formed only by the oxidation of the nitrogen of the air or of 
organic matters, if I have proved also that it is not a product 
of either animal or vegetable, I am forced to admit that 
nitre is a salt of mineral origin, that animals derive it from 
the earth, in the well or spring water which they drink, and 
which, passing into their urine, effects the nitrization of 
stones and earths, and consequently that of plants, an effect 
which may also be produced by artificial watering . — Comptes 
Rendus , No. 6, August 11, 1856. — Chemist . 
SAPPHIRES OBTAINED BY A CHYMICAL PROCESS. 
M. A. Gaudin last week communicated to the Academy 
of Sciences a process for obtaining alumina (the clay which 
yields the new metal called aluminium) in transparent crystals, 
which therefore present the same chymical composition as the 
natural stone known under the name of sapphire. To obtain 
them he lines a common crucible with a coating of lamp- 
black, and introduces into it equal portions of alum and 
sulphate of potash reduced to powder and calcined. He then 
exposes it for a quarter of an hour to the fire of a common 
forge. The crucible is then allowed to cool, and on breaking 
it the surface of the lamp*black coating is found covered with 
numerous brilliant points composed of sulphuret of potassium, 
enveloping the crystals of alumina obtained, or, in other 
words, real sapphires or corundum. The size of the crystals 
is large in proportion to the mass operated upon ; those 
obtained by M. Gaudin are about a millimetre (3*100ths of 
an inch) in diameter, and half a millimetre in height. They 
are so hard that they have been found to be preferable to 
rubies for the purpose of watchmaking. 
XXX. 
46 
