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We shall give here a brief description of the most necessary apparatus used for analysis in the dry way, and of their use.

The Blowpipe is a small instrument, made generally out of brass, silver, or German silver, and was principally used in earlier times for the purpose of soldering small pieces of metals together. It is generally made in the form of a tube, bent at a right angle, but without a sharp corner. The largest one is about seven inches long, and the smallest about two inches. The latter one terminates with a small point, with a small orifice. The first use of the blowpipe that we have recorded is that of a Swedish mining officer, who used it in the year 1738 for chemical purposes, but we have the most meagre accounts of his operations. In 1758 another Swedish mining officer, by the name of Cronstedt, published his "Use of the Blowpipe in Chemistry and Mineralogy," translated into English, in 1770, by Van Engestroem. Bergman extended its use, and after him Ghan and the venerable Berzelius (1821). The blowpipe most generally used in chemical examinations is composed of the following parts: (Fig. 1.) A is a little reservoir made air-tight by grinding the part B into it. This reservoir serves the purpose of retaining the moisture with which the air from the mouth is charged. A small conical tube is fitted to this reservoir. This tube terminates in a fine orifice. As this small point is liable to get clogged up with soot, etc., it is better that it should be made of platinum, so that it may be ignited. Two of these platinum tubes should be supplied, differing in the size of the orifice, by which a stronger or lighter current of flame may be projected from it. Metals, such as brass or German silver, are very liable to become dirty through oxidation, and when placed between the lips are liable to impart a disagreeable taste. To avoid this, the top of the tube must be supplied with a mouthpiece of ivory or horn C. The blowpipe here represented is the one used by Ghan, and approved by Berzelius. The trumpet mouthpiece was adopted by Plattner; it is pressed upon the lips while blowing, which is less tiresome than holding the mouthpiece between the lips, although many prefer the latter mode.

Dr. Black's blowpipe is as good an instrument and cheaper. It consists of two tubes, soldered at a right angle; the larger one, into which the air is blown, is of sufficient capacity to serve as a reservoir.

A chemist can, with a blowpipe and a piece of charcoal, determine many substances without any reagents, thus enabling him, even when travelling, to make useful investigations with means which are always at his disposal. There are pocket blowpipes as portable as a pencil case, such as Wollaston's and Mitscherlich's; these are objectionable for continued use as their construction requires the use of a metallic mouthpiece. Mr. Casamajor, of New York, has made one lately which has an ivory mouthpiece, and which, when in use, is like Dr. Black's.

The length of the blowpipe is generally seven or eight inches, but this depends very much upon the visual angle of the operators. A short-sighted person, of course, would require an instrument of less length than would suit a far-sighted person.

The purpose required of the blowpipe is to introduce a fine current of air into the flame of a candle or lamp, by which a higher degree of heat is induced, and consequently combustion is more rapidly accomplished.

By inspecting the flame of a candle burning under usual circumstances, we perceive at the bottom of the flame a portion which is of a light blue color (a b), Fig. 2, which gradually diminishes in size as it recedes from the wick, and disappears when it reaches the perpendicular side of the flame. In the midst of the flame there is a dark nucleus with a conical form (c). This is enveloped by the illuminating portion of the flame (d). At the exterior edge of the part d we perceive a thin, scarcely visible veil, a, e, e, which is broader near the apex of the flame. The action of the burning candle may be thus explained. The radiant heat from the flame melts the tallow or wax, which then passes up into the texture of the wick by capillary attraction until it reaches the glowing wick, where the heat decomposes the combustible matter into carbonated hydrogen (C⁴H⁴), and into carbonic oxide (CO).

While these gases are rising in hot condition, the air comes in contact with them and effects their combustion. The dark portion, c, of the flame is where the carbon and gases have not a sufficiency of air for their thorough combustion; but gradually they become mixed with air, although not then sufficient for complete combustion. The hydrogen is first oxidized or burnt, and then the carbon is attacked by the air, although particles of carbon are separated, and it is these, in a state of intense ignition, which produce the illumination. By bringing any oxidizable substance into this portion of the flame, it oxidizes very quickly in consequence of the high temperature and the free access of air. For that reason this part of the flame is termed the oxidizing flame, while the illuminating portion, by its tendency to abstract oxygen for the purpose of complete combustion, easily reduces oxidated substances brought into it, and it is, therefore, called the flame of reduction. In the oxidizing flame, on the contrary, all the carbon which exists in the interior of the flame is oxidized into carbonic acid (CO²) and carbonic oxide (CO), while the blue color of the cone of the flame is caused by the complete combustion of the carbonic oxide. These two portions of the flame—the oxidizing and the reducing—are the principal agents of blowpipe analysis.

If we introduce a fine current of air into a flame, we notice the following: The air strikes first the dark nucleus, and forcing the gases beyond it, mixes with them, by which oxygen is mingled freely with them. This effects the complete combustion of the gases at a certain distance from the point of the blowpipe. At this place the flame has the highest temperature, forming there the point of a blue cone. The illuminated or reducing portion of the flame is enveloped outside and inside by a very hot flame, whereby its own temperature is so much increased that in this reduction-flame many substances will undergo fusion which would prove perfectly refractory in a common flame. The exterior scarcely visible part loses its form, is diminished, and pressed more to a point, by which its heating power is greatly increased.

The Blast of Air.—By using the blowpipe for chemical purposes, the effect intended to be produced is an uninterrupted steady stream of air for many minutes together, if necessary, without an instant's cessation. Therefore, the blowing can only be effected with the muscles of the cheeks, and not by the exertion of the lungs. It is only by this means that a steady constant stream of air can be kept up, while the lungs will not be injured by the deprival of air. The details of the proper manner of using the blowpipe are really more difficult to describe than to acquire by practice; therefore the pupil is requested to apply himself at once to its practice, by which he will soon learn to produce a steady current of air, and to distinguish the different flames from each other. We would simply say that the tongue must be applied to the roof of the mouth, so as to interrupt the communication between the passage of the nostrils and the mouth. The operator now fills his mouth with air, which is to be passed through the pipe by compressing the muscles of the cheeks, while he breathes through the nostrils, and uses the palate as a valve. When the mouth becomes nearly empty, it is replenished by the lungs in an instant, while the tongue is momentarily withdrawn from the roof of the mouth. The stream of air can be continued for a long time, without the least fatigue or injury to the lungs. The easiest way for the student to accustom himself to the use of the blowpipe, is first to learn to fill the mouth with air, and while the lips are kept firmly closed to breathe freely through the nostrils. Having effected this much, he may introduce the mouthpiece of the blowpipe between his lips. By inflating the cheeks, and breathing through the nostrils, he will soon learn to use the instrument without the least fatigue. The air is forced through the tube against the flame by the action of the muscles of the cheeks, while he continues to breathe without interruption through the nostrils. Having become acquainted with this process, it only requires some practice to produce a steady jet of flame. A defect in the nature of the combustible used, as bad oil, such as fish oil, or oil thickened by long standing or by dirt, dirty cotton wick, or an untrimmed one, or a dirty wickholder, or a want of steadiness of the hand that holds the blowpipe, will prevent a steady jet of flame. But frequently the fault lies in the orifice of the jet, or too small a hole, or its partial stoppage by dirt, which will prevent a steady jet of air, and lead to difficulty. With a good blowpipe the air projects the entire flame, forming a horizontal, blue cone of flame, which converges to a point at about an inch from the wick, with a larger, longer, and more luminous flame enveloping it, and terminating to a point beyond that of the blue flame.

To produce an efficient flame of oxidation, put the point of the blowpipe into the flame about one third the diameter of the wick, and about one twelfth of an inch above it. This, however, depends upon the size of the flame used. Blow strong enough to keep the flame straight and horizontal, using the largest orifice for the purpose. Upon examining the flame thus produced, we will observe a long, blue flame, a b, Fig. 3, which letters correspond with the same letters in Fig. 2. But this flame has changed its form, and contains all the combustible gases. It forms now a thin, blue cone, which converges to a point about an inch from the wick. This point of the flame possesses the highest intensity of temperature, for there the combustion of the gases is the most complete. In the original flame, the hottest part forms the external envelope, but here it is compressed more into a point, forming the cone of the blue flame, and likewise an envelope of flame surrounding the blue one, extending beyond it from a to c, and presenting a light bluish or brownish color. The external flame has the highest temperature at d, but this decreases from d to c.

If there is a very high temperature, the oxidation is not effected so readily in many cases, unless the substance is removed a little from the flame; but if the heat be not too high, it is readily oxidized in the flame, or near its cone. If the current of air is blown too freely or violently into the flame, more air is forced there than is sufficient to consume the gases. This superfluous air only acts detrimentally, by cooling the flame.

In general the operation proceeds best when the substance is kept at a dull red heat. The blue cone must be kept free from straggling rays of the yellow or reduction flame. If the analysis be effected on charcoal, the blast should not be too strong, as a part of the coal would be converted into carbonic oxide, which would act antagonistically to the oxidation. The oxidation flame requires a steady current of air, for the purpose of keeping the blue cone constantly of the same length. For the purpose of acquiring practice, the following may be done: Melt a little molybdenic acid with some borax, upon a platinum wire, about the sixteenth of an inch from the point of the blue cone. In the pure oxidation flame, a clear yellowish glass is formed; but as soon as the reduction flame reaches it, or the point of the blue cone touches it, the color of the bead changes to a brown, which, finally, after a little longer blowing, becomes quite dark, and loses its transparency. The cause of this is, that the molybdenic acid is very easily reduced to a lower degree of oxidation, or to the oxide of molybdenum. The flame of oxidation will again convert this oxide into the acid, and this conversion is a good test of the progress of the student in the use of the blowpipe. In cases where we have to separate a more oxidizable substance from a less one, we use with success the blue cone, particularly if we wish to determine whether a substance has the quality, when submitted to heat in the blue cone, of coloring the external flame.

A good reduction flame can be obtained by the use of a small orifice at the point of the blowpipe. In order to produce such a flame, hold the point of the blowpipe higher above the wick, while the nozzle must not enter the flame so far as in the production of the oxidation flame. The point of the blowpipe should only touch the flame, while the current of air blown into it must be stronger than into the oxidation flame. If we project a stream, in the manner mentioned, into the flame, from the smaller side of the wick to the middle, we shall perceive the flame changed to a long, narrow, luminous cone, a b, Fig. 4, the end a of which is enveloped by the same dimly visible blueish colored portion of the flame a, c, which we perceive in the original flame, with its point at c. The portion close above the wick, presenting the dull appearance, is occasioned by the rising gases which have not supplied to them enough oxygen to consume them entirely. The hydrogen is consumed, while the carbon is separated in a state of bright ignition, and forms the internal flame.

Directly above the wick, the combustion of the gases is least complete, and forms there likewise, as is the case in the free flame, a dark blue nucleus d.

If the oxide of a metal is brought into the luminous portion of the flame produced as above, so that the flame envelopes the substance perfectly, the access of air is prevented. The partially consumed gases have now a strong affinity for oxygen, under the influence of the intense heat of that part of the flame. The substance is thus deprived of a part, or the whole, of its oxygen, and becomes reduce according to the strength of the affinity which the substance itself has for oxygen. If the reduction of a substance is undertaken on platinum, by fusion with a flux, and if the oxide is difficult to reduce, the reduction will be completely effected only in the luminous part of the flame. But if a substance be reduced on charcoal, the reduction will take place in the blue part of the flame, as long as the access of air is cut off; but it is the luminous part of the flame which really possesses the greatest reducing power.

The following should be observed in order to procure a good reduction flame:

The wick should not be too long, that it may make a smoke, nor too short, otherwise the flame will be too small to produce a heat strong enough for reduction.

The wick must be free from all loose threads, and from charcoal.

The blast should be continued for a considerable time without intermission, otherwise reduction cannot be effected.

For the purpose of acquiring practice, the student may fuse the oxide of manganese with borax, upon a platinum wire, in the oxidation flame, when a violet-red glass will be obtained; or if too much of the oxide be used, a glass of a dark color and opaque will be obtained. By submitting this glass to the reduction flame, it will become colorless in correspondence to the perfection with which the flame is produced. Or a piece of tin may be fused upon charcoal, and kept in that state for a considerable time, while it presents the appearance of a bright metal on the surface. This will require dexterity in the operator; for, if the oxidation flame should chance to touch the bright metal only for a moment, it is coated with an infusible oxide.

COMBUSTION.—Any flame of sufficient size can be used for blowpipe operations. It may be either the flame of a candle of tallow or wax, or the flame of a lamp. The flame of a wax candle, or of an oil lamp is most generally used. Sometimes a lamp is used filled with a solution of spirits of turpentine in strong alcohol. If a candle is used, it is well to cut the wick off short, and to bend the wick a little toward the substance experimented upon. But candles are not the best for blowpipe operations, as the radiant heat, reflecting from the substance upon the wax or tallow, will cause it to melt and run down the side of the candle; while again, candles do not give heat enough. The lamp is much the most desirable. The subjoined figure, from Berzelius, is perhaps the best form of lamp. It is made of japanned tin-plate, about four inches in length, and has the form and arrangement represented in Fig. 5. K is the lamp, fastened on the stand, S, by a screw, C, and is movable upwards or downwards, as represented in the figure. The posterior end of the lamp may be about one inch square, and at its anterior end, E, about three-quarters of an inch square. The under side of this box may be round, as seen in the figure. The oil is poured into the orifice, A, which has a cap screwed over it. C' is a wickholder for a flat lamp-wick. a is a socket containing the wick, which, when not in use, is secured from dirt by the cap. The figures B and a' give the forms of the cap and socket. The best combustible for this lamp is the refined rape-seed oil, or pure sweet oil. When this lamp is in use, there must be no loose threads, or no charcoal on the wick, or these will produce a smoky flame. The wick, likewise, should not be pulled up too high, as the same smoky flame would be produced.

THE SPIRIT-LAMP.—This is a short, strong glass lamp, with a cap, B, Fig. 6, fitted to it by grinding, to prevent the evaporation of the alcohol. The neck a contains a tube C, made of silver, or of tin plate, and which contains the wick. Brass would not answer so well for this tube, as the spirits would oxidize it, and thus impart color to the flame. The wickholder must cover the edge of the neck, but not fit tight within the tube, otherwise, by its expansion, it will break the glass. It is not necessary that alcohol, very highly rectified, should be burnt in this lamp, although if too much diluted with water, enough heat will not be given out. Alcohol of specific gravity 0.84 to 0.86 is the best.

This lamp is generally resorted to by blowpipe analysts, for the purpose of experiments in glass apparatus, as the oily combustibles will coat the glass with soot. Some substances, when exposed to the dark part of the flame, become reduced and, in statu nascendi, evaporated; but by passing through the external part of the flame, they become oxidized again, and impart a color to the flame. The spirit flame is the most efficient one for the examination of substances the nature of which we wish to ascertain through color imparted to the flame, as that of the spirit-lamp being colorless, is, consequently, most easily and thoroughly recognized by the slightest tinge imparted to it.

It is necessary that in operating with such minute quantities of substances as are used in blowpipe analysis, that they should have some appropriate support. In order that no false results may ensue, it is necessary that the supports should be of such a nature that they will not form a chemical combination with the substance while it is exposed to fusion or ignition. Appropriate supports for the different blowpipe experiments are charcoal, platinum instruments, and glass tubes.

(a.) Charcoal.—The value of charcoal as a support may be stated as follows: