"The outer and larger part of the flame e, d, c, which is the source of its light, is caused by the full combustion of the gases derived from the oil, wax, or tallow which rises into the wick, and is called the reducing flame, because, when concentrated upon the substance to be tested, it tends to abstract oxygen from it and thus to reduce it. In the lower part of the flame a narrow stripe of deep blue may be observed, b, c, which when acted on by the current of air from the blowpipe forms a cone, b, c, (B). This is technically called the oxidizing flame, from its property of imparting oxygen to the substance upon which it is directed. To produce the latter, the point or jet of the blowpipe should be inserted into about a third of the flame, and the assay is then to be held at the extremity of the cone of blue flame. For reduction the point of the tube should scarcely penetrate the flame, and the assay should be so placed as to be completely enveloped in it, and thus prevented from receiving oxygen.

"A little practice is sufficient to overcome the slight difficulty which at first is felt in keeping up a continual and even stream of air. The tyro may begin by accustoming himself to breathe through the nostrils whilst his cheeks are inflated, and will soon find it easy to maintain an uninterrupted supply for several minutes.

"Of the instruments used in experimenting by the blowpipe the following are the most necessary:- 1st. A pair of fine-pointed forceps, tipped with platinum. 2nd. A small spoon of platinum. 3rd. An agate pestle and mortar. 4th. Thin platinum wire and holder. 5th. A magnet. 6th. A few small tubes of thin glass. 7th. Some small porcelain capsules or saucers. "Charcoal is required as a support in many cases, particularly in the reduction of ores; and the following re-agents are also indispensable, the three first being fluxes applicable under different circumstances:

"1st. Soda, or carbonate of soda.

"2nd. Borax, or borate of soda.

"3rd. Microcosmic salt, or phosphate of soda and ammonia.

"4th. Saltpetre, to increase the degree of oxidation of certain metallic oxides.

"5th. Borax-glass, for the determination of phosphoric acid and of small quantities of lead in copper.

"6th. Nitrate of cobalt, in solution, to distinguish alumina, magnesia, and oxide of zinc.

"7th. Oxide of copper for determining small quantities of chlorine in compounds.

"8th. Fluor-spar for the recognition of lithia, boracic acid, and gypsum. "9th. Lead in a pure metallic state.

"10th Bone-ashes (9th and 10th are used for separating the silver from certain argentiferous ores).

"11th, 12th, and 13th. Hydrochloric, sulphuric, and nitric acids.

"14th. Litmus-paper, blue and red, for detecting the presence of acids and alkalies.

"The experiments on an unknown mineral must be made systematically, and referred for comparison to some list or table of minerals in which their behaviour before the blowpipe is described, as Von Kobell's tables.*

* Von Kobel, "Tafeln zur Bestimmung der Mineralien, München ;" and the same translated into English by R. Campbell.

"The first point to examine is, whether it be fusible; and, if so, in what degree. The various grades of fusibility may be conveniently divided into six; as representatives of which it is convenient to take the following minerals, species which are everywhere easy to obtain, and which may therefore be often practised upon :

"1. Antimony-Glance, or sulphide of antimony, which melts at the candle.

"2. Natrolite or Mesotype, fine splinters of which may be rounded by the candle-flame.

"3. Almandine or Precious Garnet, which fuses in large pieces before the blowpipe.

"4. Actinolite (Hornblende), fusible only in smaller portions.

"5. Orthoclase (Felspar) offers some difficulty; and

"6. Bronzite can only be rounded by the flame in the finest splinters. According to this scale, the mineral in question may be referred to either of the above numbers, or placed half-way between any two of them; as, for instance, Apophyllite, being more easily fused than Natrolite, and yet more refractory than Antimony-Glance, will have its comparative fusibility represented by 1.5.

"The fragment to be experimented upon is generally held in the platinum forceps, but it is necessary to guard against the melting of the test upon the points, since the platinum, though infusible, is by that means rendered brittle.

"In other cases the mineral may be supported upon charcoal; but whatever be the means of holding it, the phenomena exhibited by the action of the flame must be noted, as

"1st. The manner in which it fuses, whether quietly, or with decrepitation, exfoliation, intumescence, or phosphorescence; whether it loses or retains colour and transparency.

"2nd. The appearance of the product, whether a glass, an enamel, or a slag; or, as in the case of ores reduced upon charcoal, a metallic bead or regulus.

"3rd. The separation of volatile substances, and the colour of the deposit on the charcoal, by which we may recognise—

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a. Lead, giving a greenish yellow deposit.

"b. Zinc, having a white crust, which, when heated, becomes yellowish and difficult to volatilize.

"c. Antimony, a white deposit, easy to volatilize.

"d. Bismuth, a crust partly white, partly orange-yellow, without colouring the flame.

"e. Sulphur, with the well-known odour of sulphuric acid.

"f. Selenium, in an open glass tube, gives a red deposit of selenium.

"g. Tellurium, in a similar glass tube, gives a greyish-white crust of oxide.

h. Arsenic, gives off a greyish-white vapour, which smells like garlic. "i. Quicksilver, in a glass tube, will be precipitated in minute metallic globules.

"k. Water, from hydrous minerals, deposited by condensation in the

same manner.

"4th. The colour of the flame when the tip of the blue part is neatly directed upon the mineral; whence may be distinguished

“a. Red tint; given by several minerals containing strontia and (?) lithium.

"b. Green, produced by some phosphates and borates, sulphate of baryta, some copper ores and tellurium ores.

"c. Blue, given by chloride of copper, chloride of lead, &c.

"5th. The development of magnetic properties after treatment in the reducing-flame, as in ores of iron, nickel, and cobalt.

"So far the assay has been considered by itself, but it is frequently necessary to mix it with fluxes, either to render it fusible or to produce a glassy compound of a characteristic colour.

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'Thus if borax or microcosmic salt be fused into a glass at the end of a platinum wire bent into an eye, and a little powder of the unknown mineral be added to it, we shall obtain by the use of the oxidizing flame the following results:

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Manganese, in all its compounds, gives a beautiful violet or amethyst

colour.

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Cobalt causes a sapphire-blue colour; chromium an emerald-green"Oxide of iron produces a yellowish-red glass, which becomes paler as it cools, and at length grows yellow or disappears.

"Oxide of cerium gives a red or dark-yellow colour, which also grows paler as it cools.

"Oxide of nickel renders the glass a brown or violet tint, which after cooling becomes reddish-brown.

"Oxide of copper in very small quantity gives a green tint, which grows blue on cooling.

"Oxide of uranium renders the glass bright yellow, which in cooling takes a greenish tint.

"Oxide of antimony gives a pale yellow colour, which soon disappears. "When soda is used as a flux it is generally upon charcoal, and by this aid the metals may be obtained from most of their combinations in a pure state. For this purpose the powdered ore is either mixed with the moistened soda into a paste, or is enveloped in a piece of thin paper which has been dipped in a solution of soda. After fusion, that portion of the charcoal which has absorbed any of the fluid substance is to be cut off and ground down with it in the mortar, when the metal, if malleable, will at once be recognised. If several metals are combined, of which one is more easily oxidized than another, as, for instance, lead when combined with silver and copper, the latter may be separated by adding metallic lead or boracic acid, according to circumstances, and maintaining a continued oxidizing flame, till the whole of the lead has passed into the state of litharge. By means of more complete apparatus and extended operations, the most exact assays may be undertaken with the blowpipe; and those who desire a further insight into the subject may consult Plattner's 'Art of Assaying by the Blowpipe;' Berzelius On the Blowpipe;' and the beforementioned work by Von Kobell of Münich,—all of which are translated into English."

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It is almost impossible, merely by means of books, to teach the student how to recognise minerals. Still, something may be effected in that way; and the following brief hints (chiefly compiled from Dana's Mineralogy) may be of use, by enabling him, in the first instance, to ascertain to what particular class a specimen may belong; when a few essays with the blowpipe will aid him in finding out the particular species.

Thus-Carbonates may be distinguished as a class by means of Acids. Muriatic acid, generally diluted with an equal quantity of water, is the acid most frequently made use of for this purpose; but sulphuric or nitric acids, diluted in a similar manner, afford the same results. Such a solution, dropped on a carbonate (as, for instance, carbonate of lime) produces an effervescence or disengagement of bubbles of carbonic acid, which gives place to the stronger acid, for which the lime has greater affinity.

Sulphates, on the contrary, afford no effervescence with acids. When in solution, they may be tested with a solution of a salt of baryta, when they throw down a white precipitate of sulphate of baryta, which is insoluble in water. None of the sulphates possess a metallic lustre, and they are often colourless.

Nitrates, when treated with strong sulphuric acid, give off white corrosive vapours of nitric acid.

Phosphates may generally be dissolved, without change, in muriatic and nitric acids, and are decomposed by sulphuric acid. The phosphates which are soluble produce a characteristic yellow precipitate on the addition of nitrate of silver, as also do the neutral nitric solutions of the insoluble phosphates.

All the phosphates have an unmetallic lustre. None of them are soluble in water, or have any taste, except one single phosphate of ammonia. The pure phosphates also give off no odour before the blowpipe.

Silicates, in many cases, gelatinize with acids, the silica forming a jelly or separating in a gelatinous state. Sometimes this may be effected with cold acid, but, generally, the mineral, previously reduced to a finelypowdered state, is placed in strong acid, and then gently heated. After a short time, as the solution cools, the jelly appears, or, in some cases, partial evaporation is required before the jelly makes its appearance.

Borates, when reduced to powder, and heated with sulphuric acid, impart a green colour to the flame, on the addition of alcohol.

Sulphides have a metallic lustre, or an unmetallic lustre with a coloured streak; the only exceptions being Blende and Voltzite, which have an unmetallic lustre and an uncoloured streak.

Chlorides all afford a white curdy precipitate with nitrate of silver, which becomes dark or violet-coloured on exposure to the atmosphere.

Fluorides, when pulverised and heated with strong sulphuric acid in a platinum crucible, give off fumes of hydro-fluoric acid, which will corrode a plate of glass placed over the crucible.

Salts of Lime, in solution (even in a diluted state), on the addition of oxalic acid or oxalate of ammonia, afford a white precipitate of oxalate of lime, which is insoluble in water, but is very soluble in any of the stronger acids.

Iron. The protoxide salts afford a greenish-white precipitate with potash or soda, which becomes green in the first instance, and then yellow on exposure. The peroxide salts, with the same tests, afford a brown precipitate of hydrated peroxide of iron.

Compounds of Copper are, for the most part, soluble in nitric acid. Metallic iron, dipped in such a solution, becomes coated with a precipitate of metallic copper. Compounds of copper in solution, on the addition of potash or soda, yield a precipitate, which is blue at first, but turns black on being boiled; with ammonia they give a green precipitate, which is redissolved in excess of ammonia, and becomes of a fine blue colour.

Compounds of Lead, when dissolved in nitric acid, give a black precipitate with sulphuretted hydrogen (which is insoluble in excess), and a yellow precipitate with iodide of potassium or chromate of potash. Neutral solutions of lead precipitate metallic lead on metallic zinc.

Compounds of Zinc.-The sulphates afford no precipitate with sulphuretted hydrogen, but give a white precipitate with potash soluble in excess of that reagent. Acetate of Zinc affords an abundant precipitate with sulphuretted hydrogen.

Compounds of Manganese.-The salts, when heated with potash or nitrate of potash, afford manganate of potash, which gives a green solution in water, and with dilute acids a rose tint, which is destroyed by sulphurous acid or organic matters. The oxides give off chlorine when heated with muriatic acid.

Compounds of Tin form chlorides when dissolved in muriatic acid, which afford a purple colour with chloride of Gold; or if strong, a brown precipitate. Compounds of Silver.-When dissolved in nitric acid, the addition of a chloride or muriatic acid throws down a dense white curdy precipitate of chloride of silver, which turns black on exposure, and is soluble in ammonia. A slip of copper dipped in a solution of silver becomes coated with a deposit of metallic silver.

Gold is not soluble in any of the acids singly, but is dissolved by a mixture of nitric and muriatic acid (or aqua regia). The solution gives a purple precipitate on the addition of protochloride of tin, and metallic gold with protosulphate of Iron.

Platinum is not dissolved either by nitric or muriatic acid, but is dissolved in a mixture of the two. Muriate of ammonia throws down a yellow precipitate from such a solution, and the precipitate, heated in a platinum crucible, yields metallic platinum in the state of powder.

Compounds of Mercury afford a white precipitate with muriatic acid. Solutions of the protosalts give a black precipitate with potash, which is insoluble in excess of that reagent; and a black insoluble precipitate with sulphuretted hydrogen. A precipitate of metallic mercury is deposited on a slip of copper when immersed in the above solutions, and is dissipated by heat.

The various members of the Quartz family, though one of the most abundant in nature, and presenting a great diversity of colours, yet possess certain characters in common which render them easily recognisable after a little practice. The most important of these characters is the total absence of cleavage, and the degree of hardness which is No. 7 in the table given at