practising for some time to breathe calmly with puffed-up cheeks, and with the blowpipe between the lips; with a little patience the student will soon be able to produce an even and uninterrupted

current.

The supports on which substances are exposed to the blowpipe flame are generally either wood-charcoal, or platinum wire or foil.

Charcoal supports are used principally in the reduction of metallic oxides, &c., or in trying the fusibility of bodies. The substances to be operated upon are put into small conical cavities scooped out with a penknife or with a little tin tube. Metals that are volatile at the heat of the reducing flame, evaporate wholly or in part upon the reduction of their oxides; in passing through the outer flame, the metallic fumes are re-oxidized, and the oxide formed is deposited around the portion of matter upon the support. Such deposits are called incrustations. Many of these exhibit characteristic colors leading to the detection of the metals. Thoroughly-burnt pieces of charcoal only should be selected for supports in blowpipe experiments, as imperfectly-burnt pieces are apt to spirt and throw off the matter placed on them. The charcoal of the wood of pine, linden, or willow is greatly preferable for supports to that of harder and denser woods. Smooth pieces ought to be selected for supports, as knotty pieces are apt to spirt when heated, and throw off the matter placed on them. The most convenient way is to saw the charcoal of well-seasoned and straightsplit pinewood into parallelopipedic pieces, and to blow or brush off the dust; they may then be handled without fear of soiling the hands. Those sides alone are used on which the annual rings are visible as circles or segments, as on the other sides the fused matters are apt to spread over the surface of the charcoal (Berzelius).

The properties which make charcoal so valuable as a material for supports in blowpipe experiments are-1st, its infusibility; 2nd, its low conducting power for heat, which admits of substances being heated more strongly upon a charcoal than upon any other support; 3rd, its porosity, which makes it imbibe readily fusible substances, such as borax, carbonate of soda, &c., whilst infusible bodies remain on the surface; 4th, its power of reducing oxides, which greatly contributes to effecting the reduction of oxides in the inner blowpipe flame.

We use platinum wire, and occasionally also platinum foil, in all oxidizing processes before the blowpipe, and also when fusing substances with fluxes, with a view to try their solubility in them, and to watch the phenomena attending the solution, and mark the color of the bead.

The wire, which should be about the thickness of lute-strings, is

cut into lengths of three inches, and each length bent at both ends into a small loop (Fig. 10.)

Fig. 10.

When required for use, the loop is moistened with a droplet of water, then dipped into the flux, and the portion adhering exposed to the flame of a gas or spirit-lamp. The bead produced, which continues to adhere to the loop, is let cool, then moistened again, a small portion of the substance to be examined added to it, and the loop finally exposed, according to circumstances, to the inner or to the outer blowpipe flame.

What renders the application of the blowpipe particularly useful in chemical experiments is the great expedition with which the intended results are attained. These results are of a twofold kind, viz., either they afford us simply an insight into the general properties of the examined body, and enable us accordingly only to determine the class to which it belongs, i. e., whether it is fixed, volatile, fusible, &c.; or the phenomena which we observe enable us at once to recognise the particular body which we have before us. We shall have occasion to describe these phenomena when treating of the deportment of the different substances with reagents.

For most analytical purposes, the blowpipe may be replaced with great advantage and convenience by the non-luminous and smokeless flame of the Bunsen gas-lamp, which is described in the subsequent paragraphs.

& 14.

13. ALCOHOL AND GAS-LAMPS.

27

In chemical analysis the operator has constant occasion to submit substances to the influence of heat in evaporations, ignitions, &c. As for the most part small quantities of matter are employed, the requisite heat may be usually obtained from suitable lamps, for which alcohol, or better when it is at hand, illuminating gas, may serve as fuel.

ALCOHOL OR SPIRIT-LAMPS are of two kinds; the common or plain spirit-lamp (Fig. 13) is made of glass, has a ground glass cap and a brass wick-holder, and suffices to give a moderate heat for small operations. The Berzelius lamp has a hollow wick with double draught, and is much more powerful in its effects.

The form shown in Fig. 11 is convenient and serviceable. It is adjustable to any desired position upon a brass stand, which also bears a stout brass ring for supporting heavy vessels, and a second ring of slender iron wire to carry a triangle for sustaining crucibles

in the processes of ignition and fusion. The part enclosing the wick and the vessel containing the spirit of wine must be in separate pieces, connected together by means of a narrow tube; otherwise disagreeable explosions are apt to occur on lighting the lamp. The chimney must not be too narrow. The stopper on the mouth, through which the spirit of wine is poured in, must not fit air-tight.

[The Rosì and MITSCHERLICH lamps are of essentially the same construction. The stand of the former usually has a flat base, covered with a plate of porcelain, which is convenient for resting hot vessels upon. The latter is provided with a glass feeding reservoir arranged so as to maintain the alcohol about the wick, at a constant level.] Fig. 12 exhibits a triangle of platinum wire secured within a larger one of iron wire. It is useful for supporting crucibles while heating to redness.

Glass vessels, more particularly beakers, which it is intended to heat over the lamp, are mos conveniently rested on a circular piece of gauze made of fine iron wire such as is used in the making of sieves of medium fineness.

Of the many gas-lamps proposed, Bunsen's, as shown in its simplest form in Fig. 15, is the most convenient; a b is a foot of cast-iron measuring 7 centimètres in diameter. In the centre of this is fixed a square brass box, e d, which slightly slants towards the top; the sides of this box are 25 millimètres high and 16 milli mètres wide; it has a cylindric cavity 12 millimètres deep and 10 millimètres in diameter. Each side of the box has 4 millimètres from the upper rim, a circular aperture of 8 millimètres diameter,

leading to the inner cavity. One of the sides has fitted into it, about 1 millimètre below the circular aperture, a tube, d, to which is attached a vulcanized india-rubber hose, which serves to convey

the

Fig. 14.

Fig. 15.

gas to the apparatus. This tube is turned as shown in Fig. 14; it has a bore of 4 millimètres diameter. The gas conveyed into it through the india-rubber re-issues from a tube placed in the centre of the cavity of the box. This tube, which is 4 millimètres thick at the top, thicker at the lower end, projects 3 millimètres above the rim of the box; the gas issues from a narrow opening which appears formed of 3 radii of a circle, inclined to each other at an angle of 120°. The length of each radius is 1 millimètre, the opening millimètre wide; ef is a brass tube 75 millimètres long, open at both ends, and having an inner diameter of 9 millimètres; the screw at the lower end of this tube fits into a nut in the upper part of the cavity of the box. With this tube screwed in, the lamp is completed. On opening the stop-cock, the gas rushes from the opening into tube e f, when it mixes with the air coming in through the circular apertures (c). When this mixture is kindled at f, it burns with a straight, bluish flame, entirely free from soot, which may be regulated at will by opening the stopcock more or less; a partial opening of the cock suffices to give a

flame fly answering the purpose of the common simple spirit lamp; whilst, with the full stream of gas turned on, the flame, which will now rise up to 2 decimètres in height, burning with a roaring noise, affords a most excellent substitute for the Berzelius lamp. When the gas burns low, it sometimes happens that the flame recedes to the bottom of the tube fe, and burns there unmixed with air and with smoke. This difficulty is remedied by bending a bit of wire-gauze over the top of the tube fe, so as to form a movable cap. Flasks, &c., which it is intended to heat over the gas-lamp, are most conveniently supported on wire-gauze. If it is wished to use the gas-lamp for blowpipe operations, the tube g h must be inserted into ef; this tube terminates in a flattened top slanting at an angle of 68° to the axis, and having an opening in it 1 centimètre long and 1 to 2 millimètres wide; its insertion into e f serves to close up the air-apertures in the box, and pure gas, burning with a luminous flame, issues accordingly now from the top of the tube. Fig. 15 shows the apparatus complete, fixed in the forked iron stand; this arrangement permits the lamp being moved backward and forward between the prongs of the fork, and up and down the pillar of the stand. The movable ring on the same pillar serves to support the object to be operated upon. The 6 radii round the tube of the lamp serve to support a sheet-iron chimney (see Fig. 17), or a porcelain plate used in quantitative analyses.

When it is necessary to heat a crucible to an intense red, or even to a white heat, a blast-lamp must be employed. The effect of the Bunsen burner may, however, be greatly increased by a suitable clay chimney, such as recommended by O. L. Erdmann. Fig. 16 represents the arrangement. The chimney has a height of 4 inches, and is 3 inches wide in the clear. The walls are three-eighths of an inch thick. In order to make the gas-lamp serve as a substitute for the blowpipe in experiments of reduction, oxidation, fusion, &c., or in observing the coloration imparted by various substances to the flame, Bunsen* has arranged it as shown in Fig. 17. Here is seen a ring, a, which, being movable up and down on a screw, serves to regulate with perfect nicety the access of air to the flame. Again a conical sheet-iron chimney, b, which has a diameter above of 30 millimètres, below of 55 millimètres, is so placed on the radii c c, that the tube d is in its axis and terminates 45 millimètres below its upper edge. This chimney

* Ann. d. Chem. v. Pharm. 111, 257.

Fig. 16.