d f g h FIC.7. viz. 1st, a tube (a b), fitted, for greater convenience, with a horn or ivory mouthpiece, through which air is blown from the mouth; 2nd, a small cylindrical vessel (c d), into which a b is screwed airtight, and which serves as an air-chamber, and to retain the moisture of the air blown into the tube; and, 3rd, a smaller tube (f g), also fitted into the vessel (c d). This small tube, which forms a right angle with the larger one, is fitted at its aperture either simply with a finely perforated platinum plate, or more conveniently with a finely perforated platinum cap (h) screwed in air-tight. The construction of the cap is shown in Fig. 7. It is, indeed, a little dearer than a simple plate, but it is also much more durable. Whenever the opening of the cap happens to be stopped up, the obstruction may be removed by heating the cap to redness before the blowpipe. The proper length of the blowpipe depends upon the distance to which the operator can see with distinctness; it is usually from twenty to twenty-five centimètres. The form of the mouthpieces varies. Some chemists like them of a shape to be encircled by the lips; others prefer the form of a trumpet Figs. 6, 7. mouthpiece, which is only pressed against the lips. The latter require less exertion on the part of the operator, and are accordingly generally chosen by those who have a great deal of blowpipe work. The blowpipe serves to conduct a continuous fine current of air into a gas-flame, or into the flame of a candle or lamp. The flame of a candle (and equally so that of gas or of an oil lamp), burning under ordinary circumstances, is seen to consist of three distinct parts, as shown in Fig. 8, viz., 1st, a dark nucleus in the centre (a); 2nd, a luminous cone surrounding this nucleus (e fg); and, 3rd, a feebly luminous mantle encircling the whole flame (b c d). The dark nucleus is formed by the gases which the heat evolves from the wax or fat, and which cannot burn here for want of oxygen. In the luminous cone these gases come in contact with a certain amount of air insufficient for their complete combustion. In this part, therefore, it is principally the hydrogen of the Fig. 8. On the other hand, oxides having a tendency to yield up their oxygen, suffer reduction when placed within the luminous part of the flame, the oxygen being withdrawn from them by the carbon and the still unconsumed carbide of hydrogen present in this sphere. The luminous part of the flame is therefore called the reducing flame. Now the effect of blowing a fine current of air across a flame, is first to alter the shape of the latter, which, from tending upward, is now driven sideways in the direction of the blast, and at the same time lengthened and narrowed; and, in the second place, to extend the sphere of combustion from the outer to the inner part. As the latter circumstance causes an extraordinary increase of the heat of the flame, and the former a concentration of that heat within narrower limits, it is easy to understand the exceedingly energetic action of the blowpipe flame. The way of holding the blowpipe and the nature of the current, will always depend upon the precise object in view, viz., whether the operator wants a reducing or an oxidizing flame. The easiest way of producing most efficient flames of both kinds is by means of coal-gas delivered from a tube, terminating in a flat top with a somewhat slantingly downwardturned slit 1 centimètre long and 1 to 2 millimètres wide; as with the use gas the operator is enabled to control and regulate not only the blowpipe flame, but the gas stream also. The task of keeping the blowpipe steadily in the proper position may be greatly facilitated by firmly resting that instrument upon some moveable metallic support, such as, for instance, the ring of Bunsen's gas lamp for supporting dishes, &c. Fig. 9 shows the flame for reducing, Fig. 10 the flame for oxidizing. The luminous parts are shaded. of Fig. 9. The reducing flame is produced by keeping the jet of the blowpipe just on the border of a tolerably strong gas flame, and driving a moderate blast across it. The resulting mixture of the air with the gas is only imperfect, and there remains between the inner bluish part of the flame and the outer barely visible part a luminous and reducing zone, of which the hottest point lies somewhat beyond the apex of the inner cone. To produce the oxidizing flame, the gas is lowered, the jet of the blowpipe pushed a little further into the flame, and the strength of the current somewhat increased. This serves to effect an intimate mixture of the air and gas, and an inner pointed, bluish cone, slightly luminous towards the apex is formed, and surrounded by a thin, pointed, light-bluish, barely visible mantle. The hottest part of the flame is at the apex of the inner cone. Difficultly fusible bodies are exposed to this part to effect their fusion; but bodies to be oxidized are held a little beyond the apex, that there may be no want of air for their combustion. An oil-lamp with broad wick of proper thickness may be used instead of coal-gas; a thick wax candle also will do. For an oxidizing flame, a small spiritlamp will in most cases answer the purpose. Fig. 10. The current is produced with the cheek muscles alone, and not with the lungs. The way of doing this may be easily acquired by 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 the 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 straight-split 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 8 centimètres, and each length twisted at both ends into a small loop (Fig. 11). Fig. 11. When required for use, the loop is moistened with a drop 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. APPENDIX TO SECTION I. $14. APPARATUS AND UTENSILS. As many students of chemical analysis might find some difficulty in the selection of the proper apparatus, &c., I append here a list of the articles which are required for the performance of simple experiments and investigations, together with instructions to guide the student in the purchase or making of them. 1. A BERZELIUS SPIRIT-LAMP, with suitable stand. 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 most inconvenient 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 airtight. The stand must be fitted with proper brackets, and also with a moveable brass ring to support dishes and flasks in processes of ebullition, and a ring of moderately stout iron wire to support the triangle for holding the crucibles in the processes of ignition and fusion. Of the various forms of lamps to be had, the one shown in Fig. 12 is the most suitable and elegant. Fig. 13 shows a triangle of platinum wire fixed within an iron wire triangle; this is the most suitable construction for supporting the crucible in processes of ignition. Glass vessels, more particularly beakers, which it is intended to heat over the lamp, are most 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. 2. A GLASS SPIRIT LAMP, with ground glass cap and brass wick-holder. (Fig. 14.) In towns lighted by gas, spirit lamps are now almost entirely superseded by gas lamps. 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, c d, which slightly slants towards the top; the sides of this box are 25 millimètres high and 16 millimètres 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 a Fig. 15. g h |