b. Brucite, when moistened, after being treated on charcoal, reacts alkaline with reddened litmus paper. It comports itself towards fluxes similarly to magnesia.

c. Carbonate of Magnesia :

1 Magnesite, when not contaminated, behaves like Brucite : 2 Carbonate of Magnesia with Carbonate of lime, as Dolomite, Brown Spar, et cetera.

These compounds behave like carbonate of lime before the Blowpipe, so that the magnesia cannot be distinguished from the lime. It must, therefore, be obtained after separating the iron and lime, by the process previously given as ammonia-phosphate, and then treated on charcoal per se, and also with equal parts of soda and nitre upon the platinum wire. It ought to melt to a white crystalline pearl, easily soluble in microcosmic salt, provided no trace of manganese is present, producing a colorless glass, remaining so when brought in contact with a crystal of saltpetre. The smallest portion of manganese, if present, will be infallibly detected by treating the precipitated magnesia with soda and nitre on platinum foil.

If an appreciable quantity of manganese is contained in the specimen, it is better to precipitate it by sulphide of ammonium; then filter, and free the solution from sulphide of hydrogen, as given in the lime examination.

d. Sulphate of Magnesia-Epsomite-is immediately recognized on treating with a solution of nitrate of cobalt.

e. Boracite fuses with intumescence on charcoal; it is difficult to obtain a clear pearl, as it becomes drusy upon cooling; that is, the whole surface of the charcoal presents crystalline needles. The glass while hot appears slightly yellowish, from the presence of sesquioxide of iron, but on refrigeration it is opaline. It readily dissolves in borax, forming a transparent ferruginous colored glass.

Boracite also dissolves with facility in microcosmic salt to a clear glass, here and there turbidly streaked, and if an excess is present, the bead will be opaque when cold.

When it is melted with carbonate of soda sufficient to produce a clear glass, the assay on cooling presents crystals and large

facets. With more of the alkali, the glass is similar to a magnesian bead not sufficiently saturated. Heated in a powdered state upon charcoal, with a few drops of a cobalt solution, the whole concretes forming a blue mass.

When melted with bisulphate of potassa, and the fused assay dissolved in water, the magnesia can be precipitated and examined as before stated.

Should the Boracite contain borate of lime also, it is readily discovered by adding to the aqueous sulphate solution a little chloride of ammonium, and then oxalate of ammonia, before precipitating the magnesia with microcosmic salt.

The Boracic Acid is determined according to the process given under this head.

f. In Silicates, in which magnesia forms the only base, exempli gratia, Speckstein, Meerschaum, Picrosmine, and Serpentine, the magnesia is ascertained the most readily by smelting the mineral with bisulphate of potassa, and treating the vitreous residue with water; by this means the insoluble silicic acid is separated, and the filtrate, containing sulphate of magnesia, can be heated with microcosmic salt, and examined as before remarked. If the mineral contains lime, as Olivine, it must be separated previously to precipitating the magnesia. Silicates containing several bases, to which the majority of the prepared ores and slags belong, cannot have the magnesia determined with certainty before the Blowpipe, either alone or with bisulphate of potassa; therefore, they must be examined in the same manner as given under Baryta and Lime. The precipitation of the Basic Ammoniaphosphate of Magnesia, is greatly facilitated when the menstruum is boiled. When there is a very small quantity of magnesia present, it is better to allow the liquid, after the addition of the precipitant, to repose for some hours.

§ 9. ALUMINA—Ál2 O3—Presence in the Mineral Kingdom.

Alumina is very abundant, being found,—

a. As pure Alumina, with slight traces of Silica and Ses

K

quioxide of Iron, in Corundum, Sapphire, Ruby, and Diamant Spar;

b. As Hydrate of Alumina, in Diaspore [Al2 03 + aq]; and Gibbsite [Al2O3 + 3 aq];

c. With Magnesia, as Magnesia-Alumina, in Spinel; with Protoxide of Iron, as Ferruginous Aluminate of Magnesia, in Zeylanite; with Oxide of Zinc, et cetera, Zincous Alumina, in Automalite-Gahnite-Mg } Al2 O3]; and with Oxide of Lead,

Zn

[Fe

as Aluminate of Lead, in Plombgomme [Pb O, Alo 03 + 6 aq]; d. With Fluorine and Fluoride of Sodium, in Cryolite [3 (Na FI) + Al2 03, 3 Fl] ;

e. With Sulphuric Acid and Water, in Aluminite [Alo 03, SO39 aq]; with Sulphuric Acid, Potassa, and Water, in Potassa-Alum; with the same constituents without Potassa, but with Ammonia, in Ammonia-Alum; and with Sulphuric Acid, Potassa, Sesquioxide of Iron, and Water, in Iron-Alum;

Formula for the two above-mentioned Alums: Potassa-Alum [K O, S 03 + Al2 O3, 3 S 03 + 24 aq]; Ammonia-Alum [N H4 O, S 03 + Al2 03, 3 S 03 + 24 aq]; Iron-Alum [K O, S 03 + Fe2 03, 3 S O3 + 24 aq];

f. With Phosphoric Acid and Lithia, in Amblygonite: with Phosphoric Acid, Water, a little Fluorine, Lime, Protoxides of Iron and Manganese, in Warellite [2 Al, 3 Fl + 3 (4 Al2 03, 3 P05) + 18 aq]; with Phosphoric Acid, Magnesia, Silica, Protoxide of Iron, and Water, in Lazulite [3 (5 Mg 0, 2 P 05) + 4 (5 Al2 03, 3 P 05) + 4 Fe 0, P 05 + 15 aq] et cetera, in varying proportions;

g. In Silicates, exempli gratia.

1 Where Alumina is the only base, as in Cyanite [2 Alo 03, Si 02, + 3 (Al2 O3, Si O2) ] ;

2 In Silicates of Potassa and Lime; exempli gratia, in Zoisite -Epidote ;

3 In Silicates of an Alkali, or of an Alkaline Earth, and Silicates of Alumina, combined with water of crystallization. To O+

-3 Ca O
3 Na

these belong Chabasite [No Si O2 + 3 (Al O3, 2 Si 0o) +

15 aq]; Mesolite [Na O, Si O2 + Al2 03, Si O2 + 2 aq + 2 (Ca O, Si O2 + Ale 03, Si O2 + 6 aq) ]-Mesolite may be considered as a mixture of Mesotype and Scolezite; Mesotype [Ca O, Si O2 + Al2 03, Si O2 + 3 aq]; Anaclime [3 Na O, 2 Si 02 + 3 (Al O3, 2 Si 0°) + 6 aq]; Stilbite Lamonite, Harmotome, Prehnite, et cetera.

4 In Silicates of the Alkalies or Alkaline Earths, with Silicates of Alumina, without water; exempli gratia, Felspar, Albite, Petalite, Spodumene, Leucite, Labradorite, Scapolite; the formula of the last is [383 2 Si O2 + 2 (Al2 03, Si Oo)]; further, in Elaolite [3K 0} Si O2 + 3 (Alo 03, Si Oo) ]; Sodalite, Anorthite, et cetera ;

Na

Ca

Na

5 In Silicates of Potassa or Lithia, with Silicates of Magnesia, Alumina Protoxide of Iron, and Manganese, without water; in Mica, which sometimes contains Fluorine;

6 In Silicates of Potassa or Soda, with Silicates of Magnesia, Alumina, and Protoxide of Iron, with and without water, in which the alkalies are more or less replaced by magnesia or protoxide of iron; exempli gratia, in Potstone, Green-earth, Chlorite, and Tale;

7 In Silicates of Lime and Magnesia with Alumina, in which the alkaline earths are often replaced by the protoxides of iron and manganese; as in Pistacit, Idiocrase; in many varieties of Garnets; in Gehlenite, Soapstone Dichroite, and Karpholite; the last sometimes contains traces of Fluorine, its general formula is [3 Mn 0} Si O2 + 3 (Al2 O3, Si O2) + 6 aq ;

Fe

Si

8 In Silicates of Alumina and Metallic Oxides; exempli gratia, in Staurolite, from St. Gothard [3303} {203]; and AlloA120332 A12 phane, from Schneeberg, which contains Oxide of Copper.

Fe

9 In Silicates containing Glucina; for instance, Emerald and Beryl, the formula for both of which is [33033 8 Si Oo]. When the former is tinged green by Oxide of Chromium, it is the true Emerald, but when perfectly colorless and transparent, it is the aqua marina, which is a most valuable gem : further, in Euclase [Si Oo]; and in Cymophane, or Chrysoberyl [4 Al2 03, Si O2 + 2 (Gl2 O3, 4 Al2 O3) ] ;

10 In Silicates which contain Yttria and Oxide of Cerium ; as Cerine, Allanite, Orthite, and Pyrorthite;

11 In Silicates containing Fluorides; for example, Topaz [Al2 03 + 2 (2 Al 3 Fl) + 6 (Al2 03, Si 02) ] ;

12 In Polybasic Silicates, which contain small quantities of one or more Borates, as the various Tourmalines [K O, Li O, Na O, Ca O, Mg O, Fe 0, Mn O, Al2 O3, Si O2, B O3]; and in Axinite· O'SULLIVAN has examined many of the Tourmalines, and always found in them more or less Manganese and Lime.

13 In Silicates of Soda, Lime, and Magnesia, combined with Sulphates; as, Lazulite, Nosin, et cetera. Alumina is also met with in Kryolite, Bleigummi, Pissophane, Thonerde, Peganite, Striegisane, Variscite, Honeystone, Andalusite, Sillimanite, Bucholsite, Xenolite, Ramlite, Worthite, Kollyrite, Miloschine, Pholerite, Tuesite, Gilbertite, Anauxite, Kaolin, Halloysite, Nakrite, Ottrelite, Cimolite, Bolus, Plinthite, Orthite, Malthacite, and Pyknite.

h. In various kinds of rocks; exempli gratia, Fuller's Earth, Common Clay, Loam, Marl, Porphyry, Garnet, Mica Slate, Clay Slate, Alum Slate, Sandstone, Gneiss, et cetera. Clay Slates, et cetera, besides the usual given constituents, contain traces of Sulphur, Phosphoric Acid, Chlorine, and Fluorine.

As metallic gangues are generally classed under one or the other of the above mentioned rocks, and as, in obtaining the ores, the adhering stony matrix cannot be completely separated from the former, therefore, it is that alumina generally forms a considerable constituent of many ores prepared in the dry way, and, consequently, an ingredient of the slags obtained in the smelting of such ores.

Examination for Alumina.

a. Corundum, Sapphire, Ruby, and Diamant Spar comport themselves before the Blowpipe, as follows:

Alone, they remain perfectly unchanged, as well in a powdered state as in fragments.

With borax they fuse perfectly, though with difficulty, to