ON" THE RUBIES OF BURMA AND ASSOCIATED MINERALS. 
217 
If we now turn our attention to the processes which have been devised for causing 
aluminium oxide to assume the crystallized form, and thus produce corundum, we 
shall find that no less than twenty methods are now known by which this end may 
be attained. They are as follows :— 
1. Fusing aluminium oxide in oxyhydrogen flame (Gaudin, 1869). 
2. Heating alum alone or with potassium sulphate (Gaudin, 1839). 
3. Heating aluminium chloride in closed tube (suggested by Gay Lussac, accom¬ 
plished bv Meunier, 1880). 
4. Heating aluminium oxide with borax (Ebelmen, 1851). 
5. Heating aluminium fluoride with boric acid (Deville and Caron, 1857). 
6. Acting on aluminium oxide, at a red heat, with hydrofluoric acid (Haute- 
FEUILLE, 1865). 
7. Heating sodium aluminate with hydrochloric acid (Debray, 1865). 
8. Heating aluminium phosphate with potassium sulphate (Debray, 1865). 
9. Heating aluminium oxide with minium in a crucible (Fremy and Feil, 
1877). 
10. Heating aluminium oxide with a fluoride in the presence of an alkali (FrLmy 
and Verneuil, 1887). 
11. Melting together microcline and fluorspar (Fouque and M. Levy, 1 884). 
12. Heating to redness for one hour cryolite and a silicate (Lacroix, 1887). 
13. Heating aluminium oxide with silica and cryolite (Meunier, 1880). 
14. Melting nepheline (P. Hautefeuille and A. Perrey, 1890). 
15. Acting on aluminium oxide by water at a red heat (Meunier, 1880). 
16. Heating aluminium oxide with soda to 530° to 535° C. for 20 hours (Friedel, 
1891). 
17. Heating solution of aluminium chloride to 350° G. in closed vessel (Senarmont, 
1850). 
18. Heating solution of aluminium nitrate to 350° C. in closed vessel (Senarmont, 
1850). 
19. Heating aluminium oxide with water and trace of ammonium fluoride to 
300° C. for 10 hours (Bruhns, 1889). 
20. Heating solution of aluminium sulphate in closed tube to 160° to 180° C. 
(Weinschenk, 1890). 
It would be rash to suggest that any one of the methods enumerated above was 
the one by which corundum has been naturally produced in any particular rock. 
But it is evident that by these, or similar, reactions, crystallized aluminium oxide 
may have been formed in deep-seated rocks, under enormous pressure, at even 
moderate temperatures, and that, with sufficient time, the crystals may have grown 
to considerable dimensions. 
2 F 
MDCCCXCYI.—A. 
