That this method is not applicable to the examination of readily fusible metallic alloys, is easily understood; for, on melting, they flow out from the tube, which is held obliquely.

When the substance is in combination with sulphur, it escapes as sulphurous acid, which is recognized by its characteristic odor; and in this case, if only a small portion of antimony be contained in the assay, antimonious acid will often be generated, and no oxide of antimony. If the substance contains much arsenic, the antimonial vapor will be very profuse; but, as the crystals of oxide of antimony and arsenious acid combine, they cannot always be distinguished from their appearances. When this ensues, it is preferable to examine on charcoal, as previously described.

Combinations of oxides of antimony, or antimonious acid, and other bodies, cannot always be examined with certainty in an open glass tube for antimony, it is always better to employ the procedure with soda, on charcoal.

§ 18. MOLYBDENUM-Mo-Presence in the Mineral Kingdom.

It is found

a. Metallic, combined with Sulphur, in Rhombohedral Molybdena Glance [Mo 2 S];

b. As Molybdic Acid [Mo 03], per se as a yellow coating upon the Sulphide of Molybdenum, and with Oxide of Lead, in GelbBleierz-Molybdate of Lead.-BOUSSINGAULT found, in Basic Molybdate of Lead, from Paramo-Rico-near Pamplona, in South America,-Lead, Molybdic Acid, Carbonic Acid, Hydrochloric Acid, Phosphoric Acid, Chromic Acid, Sesquioxide of Iron, Alumina, and Silica.

Examination for Molybdenum.

The molybdenum in Molybdena-Glance is detected by means of microcosmic salt upon the platinum wire. This flux appears at first not to dissolve any of the mineral, but, after a long-continued oxidating flame, the microcosmic bead assumes a greenish color, owing to molybdic acid. If the undissolved portion of the

assay be removed with a forceps from the molten bead, and what remains treated with a reducing flame, the green color will be very characteristic. Molybdic acid, before the Blowpipe, fuses on charcoal, volatilizes, and imparts to the flame a yellowish-green tinge; and where the assay rested, a reddish shining metallic speck is observed. The acid deposits also a crystalline coating upon the charcoal. Sulphide of Molydenum, and also the metal, give, without fusing, the same reaction. The green color imparted to borax by molybdic acid remains perfectly transparent, after exposure for a very long time to the oxidating flame; therefore the operator may rest satisfied that this reaction proceeds from no other metallic oxide.

The Native Molybdic Acid from Bispberg comports itself in a similar manner to the pure acid, but when treated with soda upon charcoal, it is imbibed, and peroxide of tin remains behind.

Gelb-Bleierz is submitted to the same treatment as the Molybdena Glance, for the detection of the molybdic acid; with this precaution, that too much of the specimen be not added, or otherwise a black opaque glass will result.

MERLET'S moist method for the detection of molybdenum in the foregoing minerals, is the following: powder the specimen, and fuse with nitre in a platinum spoon; molybdate of potassa is formed. Dissolve in a porcelain basin with water over a spiritlamp; decant off the clear solution into another vessel, in order to get rid of the residuary matters that perhaps may occur; and then treat the hot aqueous solution with hydrochloric acid, and immerse in the menstruum a strip of metallic copper. If only a trace of molybdic acid be present, the liquid, where the copper rests, will acquire a beautiful blue color, which disappears as the solution cools, but is immediately restored by heat. Metallic molybdenum, which is obtained by fusing the oxide in a crucible lined with charcoal, is not fusible before the Blowpipe; but when heated upon charcoal, in the oxidating flame, it becomes oxidized; and gradually coating, at no great distance from the assay, the support with a sublimate, which in many places, but particularly nearest the assay, is in transparent silky shining crystalline plates also in a pulverulent form. The deposit of molybdic acid is,

while hot, yellow; and when cold, white. The crystalline plates appear the most beautiful when the assay is kept far from the Blowpipe flame; but the heat must be properly regulated for their formation. The sublimate can be driven along the charcoal by the oxidating flame; but the place which it leaves appears, when perfectly cold, dark copper-red, and shining oxide of molybdenum remains, which is produced by the molybdic acid coming in contact with the glowing charcoal. Molybdenum remains intact in the reducing flame.

Sulphide of Molybdenum-Molybdena Glance—which is also infusible, affords, in a continued strong oxidating flame, the same sublimate as pure Molybdenum, while its sulphur escapes as sulphurous acid.

Molbydic Acid fuses very readily, volatilizes in the oxidating flame, coating the charcoal with crystalline acid, and copper-red metallic shining oxide. Molybdenum possesses, in an oxidized condition, the property of tinging the outer Blowpipe-flame; thus, if molybdic acid, in a moistened state, be treated on platinum wire with the apex of the blue flame, it volatilizes, coloring the outer flame yellowish-green, analogous to baryta. The same coloration is produced by Molybdena Glance, as may be seen by heating a thin fragment of this mineral, held in the platinum forceps, in the apex of the blue flame. No fusion takes place, but the outer flame assumes a yellowish-green color.

§ 19. TUNGSTEN-W-Presence in the Mineral Kingdom.

This element exists in nature as an Acid only, either per se [W O3], or in combination with Bases, namely:-with Lime, in Schwerstein-Tungstate of Lime-[Ca O, W O3]; with Oxide of Lead, in Tungstate of Lead-Scheelbleispath;—with Iron, and Protoxide of Manganese, in Wolfram [Mn 0, W 03 + 3 (Fe O, W O3)]-its composition has been represented by BERZELIUS as follows: [Fe2 03, 2 W 03 + Mn2 03, 2 W 03]; further, as a very small ingredient in some varieties of Tantalite, and in Black and Brown Yttro-Tantalite.

Examination for Tungsten.

Tungstic acid is readily detected in Schwerstein, Wolfram, and Tungstate of Lead, in the following manner: Mix a small portion of powdered mineral with five times its volume of soda, and heat the mass strongly in a platinum spoon. Dissolve the fused assay in boiling water, and decant off the supernatant clear liquor, which contains tungstate of soda. If this solution be treated with hydrochloric acid, a white powder deposits, which, when heated, assumes a beautiful lemon color. The behavior of the tungstic acid in Schwerstein, towards microcosmic salt, has been previously given at page 120.

When the Tantalites are examined in this manner for tungstic acid, tantalic acid,-if the tantalium is contained as an acid,will accompany tungstic acid, which prevents the yellow reaction. when heat is applied to the mixture. Should this occur, the white powder must be separated from the solution by filtration, edulcorated, and treated with microcosmic salt, as follows: dissolve in the microcosmic salt upon a plantinum wire, so much sesquioxide of iron that the glass produced will appear colorless or slightly yellow in the oxidating flame, and, when treated in the reducing flame, perfectly colorless when cold. Now add some of the moist precipitate, and submit the whole, first to an oxidating and then to a reducing flame. If tungstic acid be present, the glass will be tinged, either yellow, red, or blood-red, according to the quantity of the substance added. As mistakes may arise, on account of titanic acid affording, with microcosmic salt, a similar reaction to tungstic acid, the examination should be extended. According to ROSE, tungstic acid gives a yellow glass with borax, and titanic acid, a violet one, which becomes turbidly streaked.— This reaction is so exceedingly accurate, that if a trace only of tungstic acid be contaminated with the tantalic acid, the ferruginous microcosmic glass will acquire a yellowish hue. The operator must exercise great care in adding the sesquioxide of iron, to avoid a blue reaction being obtained in the reducing flame. As nearly all Tantalites contain more or less sesquioxide of iron, this method will very seldom have to be employed, as the reaction

is speedily produced by dissolving the pulverized mineral in microcosmic salt, and treating in the reducing flame; if tungstic acid be present, a transparent dark red bead results. The presence of protoxide of manganese, oxides of tin, yttria, and lime, does not affect the coloration.-Tungstic acid is most conveniently obtained by decomposing the native Tungstate of Lime, finely pulverized, by hydrochloric acid; chloride of calcium is formed, and tungstic acid precipitates. Dissolved in ammonia, and precipitated again by acid, tungstic acid always forms a compound with the acid employed. It may be obtained in a separate state, by heating the tungstate of ammonia to redness. It is an orangeyellow powder, which becomes dull green when strongly heated. It is quite insoluble in water, and in acids, but dissolves in alkaline solutions.

Titanic acid, oxide of nickel, and antimonious acid, when combined with small quantities of iron, give similar reactions with microcosmic salt, as ferruginous tungstic acid.

§ 20. VANADIUM-V-Presence in the Mineral Kingdom.

It has been found in an Iron Ore from Taberg; a Lead Ore from Zimapan, in Mexico, also from Warloch-head in Scotlandwhich is principally Vanadiate of Lead;-in Volborthite, Pea Iron Ore, from Steinlade, near Goslar; in Mansfield Copper Slate, Hydrophite, and Vanadiate of Lime. The presence of Vanadium in Pitchblende most probably arises from the presence of Vanadiate of Lime, the recently discovered mineral.

Vanadium is a very rare element.

Examination for Vanadium.

The pyrognostic properties of Vanadiate of Lead are very characteristic. On charcoal, before the Blowpipe, it strongly decrepitates, fuses to a globule, then scintillates, giving a regulus of lead, and the support becomes coated with a yellow sublimate.

With microcosmic salt, it gives in the oxidating flame, a reddishyellow, and, after cooling, a yellowish-green glass; in the reducing flame, it affords a beautiful chrome-green bead.