Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/855

Anglicus " the union of Scottish melody with the English is first conspicuous." Blow died in 1708, and was buried in the north aisle of Westminster Abbey. None of his compositions, most of which are anthems, attain the highest

order of merit.

BLOWPIPE, a tube for directing a jet of air into a fire or into the flame of a lamp or gas jet, for the purpose of producing a high temperature by complete and rapid com bustion. The blowpipe has been in common use from the earliest times for soldering metals and working glass ; and since 1733, when Anton Swab first applied it to analysis of mineral substances,- it has become a valuable auxiliary to the mineralogist and chemist, in the chemical examina tion and analysis of minerals. Its application has been variously improved at the hands of Cronstedt, Bergmaun, Galm, Berzelius, Plattner, and others, but more especially by the two last-named chemists.

FIG. 1. Extremities of Gahn s Blowpipe, ordinary size.

The simplest and oldest form of blowpipe (still used by gasntters, jewellers, &c.), is a conical brass tube, about 7 inches in length, curved at the small end into a right angle, and terminating in a small round orifice, which is applied to the flame, while the larger end is applied to the mouth. Where the blast has to be kept up for only a few seconds, this instrument is quite serviceable ; but in longer chemical operations inconvenience arises from the condensation of moisture exhaled by the lungs in the tube. Hence many blowpipes are made with a cavity for retaining the moisture. Cronstedt placed a bulb in the centre of his blowpipe. Dr Black s convenient instrument consists of a conical tube of tin plate, with a small brass tube, support ing the nozzle, inserted near the wider end, and a mouth piece at the narrow end. One of the most suitable forms of blowpipe is that shown in fig. 1. It is Gahn s instrument as improved by Plattner. The tube A is ground to fit accurately into a socket at the top of the water-trap B, as is also the jet-pipe C. The nozzle D, of platinum, is fitted in the same manner, so that it can be easily removed and replaced while hot ; e.g. when it is desired to remove the crust of soot which deposits upon the point when an oil lamp or caudle is used. The sizes of orifice recom mended by Plattner are 04 and 5 millim. The trumpet mouthpiece, from the support it gives to the cheeks when inflated, conduces to a more steady and long-continued blast being kept up without fatigue than when the mouthpiece is inserted between the lips. Mr David Forbes has sug gested the use of a double jet-pipe in connection with this instrument, so that a large or small orifice may be obtained without stopping the point ; but it is doubtful whether the advantage gained is counterbalanced by the extra cost and complication. For the majority of blowpipe workers, there is probably no better instrument than Dr Black s, if pro vided with a properly-shaped nozzle, if possible of platinum; but where it is much used, the large-sized trumpet-mouthed instrument of Plattner is to be pre ferred. The instrument should be held with the first and fourth fingers passed round it, and the thumb laid along the side of the tube, the hold being steadied by resting the elbow on the table. The mode of blowing is peculiar, and requires some practice ; an uninterrupted blast is kept up by the muscular action of the cheeks, while the ordinary respiration goes on through the nostrils.

If the flame of a candle or lamp be closely examined, it will be seen to consist of four parts (a) a deep blue ring at the base, (6) a dark cone in the centre, (c) a luminous portion round this, and (d) an exterior pale blue envelope. The blue ring is formed chiefly by combustion of carbonic oxide. In the central cone the combustible vapours frotn the wick, though heated, are not burned, atmospheric oxygen not reaching it. In the luminous portion the supply of oxygen is not sufficient for complete combustion ; the hydrogen takes up all or most of it, and carbon is pre cipitated in solid particles and ignited. In the exterior envelope, lastly, the temperature is highest, and combustion most complete, sufficient oxygen being supplied to con vert the carbon and hydrogen into water and carbonic acid.

In bbwpipe work only two of these four parts arc made use of, viz., the pale envelope, for oxidation, and, the luminous portion, for reduction. To obtain a good-. oxidizing flame, the blowpipe is held with its nozzle inserted in the edge of the flame close over the level of the wick, aud blown into gently and evenly. A conical jet is thus produced, consisting of an inner cone, with an outer one com mencing near its apex: the former, corresponding to () in the free flame, blue and well defined ; the latter, corre sponding to (d), pale blue and vague. The heat is greatest just beyond the point of the inner cone, combustion being there most complete. Oxidation is better effected (if a very high temperature be not required) the farther the substance is from the apex of the inner cone, so far as the heat proves sufficient, for the air has thus freer access.

To obtain a good reducing flame (in which the com bustible matter, very hot, but not yet burned, is disposed to take oxygen from any compound containing it), the nozzle, with smallev orifice, should just touch the flame at a point higher above the wick, and a somewhat weaker current of air should be blown. The flame then appears as a long, narrow, luminous cone, the end being enveloped by a dimly visible portion of flame corresponding to that which surrounds the free flame, while there is also a dark nucleus about the wick. The substance to be reduced is brought into the luminous portion, where the reducing power is strongest.

The flame of an oil-lamp is the best for blowpipe opera

tions where gas is wanting ; candle flame may be used when great heat is not required. The blowpipe lamp of Berzelius, supplied with colza oil, is probably the most suitable. The wick, when in use, should be carefully trimmed and clean, so as to avoid a smoking flame. The general introduction of gas has quite driven out the use of oil-lamps for blowpipe purposes in laboratories. Various materials are used as supports for substances in the blowpipe flame; the principal are charcoal, platinum, and glass. Charcoal is valuable for its infusibility aud low conductivity for heat (allowing substances to be strongly heated upon it), and for its powerful reducing agency by the production of carbonic oxide when ignited ; so that it is chiefly employed in trying the fusibility of minerals, aud in reduction. The best kind of charcoal is that of close-grained pine or alder; it is cut in short prisms, having a flat smooth surface at right angles to the rings of growth. In this a shallow hole is made with a knife or borer, for receiving the substance to be held in the flame. Platinum is employed in oxidizing processes, and in fusion of substances with fluxes with a view to try their solubility in them, and note the phenomena of the bead ; also in observing the colouring effect of substances on the

blowpipe flame (which effect is apt to be somewhat masked