The most intense heat of the common blowpipe is that of the pointed flame; with a thick wax candle, and a blowpipe with a small aperture placed slightly within the flame, the mineralogist succeeds in melting small fragments of all the metals, when they are supported upon charcoal, and exposed to the extreme point of the inner or blue cone, which is the hottest part of the flame; that is, fragments of all metals which do not require the oxy-hydrogen blowpipe.

Larger particles, requiring less heat, arc brought somewhat nearer to the candle, so as to receive a greater portion of the flame; and when a very mild degree of heat is needed, the object is removed further away, sometimes as in melting the fluxes preparatory to soldering, even to the stream of hot air beyond the point of the external yellowish flame.

The first or the silent pointed flame, is used by the chemist and mineralogist for reducing the metallic oxides to the metallic state, and is called the deoxidizing flame; the second, or the noisy brush-like flame, is less intense, and is called the oxidizing flame.

* The inventions of Bergman, Black, Gahn, Macgellan, Pepys, Teunant, Wollaston, etc.

The artizan employs in soldering a much larger flame than the chemist, namely that of a lamp the wick of which is from a quarter to one inch diameter, this must be plentifully supplied with oil; the blowpipe in such cases is selected with a larger aperture; it is blown vigorously, and held a little distant from the flame, so as to spread it in a broad stream of light, extending over a large surface of the work, which is in most cases supported upon charcoal. When any minute portion alone is to be heated, the pointed flame is used with a milder blast of air and a decreased distance.

The Modes Of Applying Heat In Soldering Continued 100150

Fig. 306 is an arrangement, the use of which is attended with no fatigue to the operator; it is much employed by the cheap jewelry manufacturers at Birmingham. A stream of air from a pair of bellows directs a gas flame through a trough or shoot, the third of a cylindrical tube placed at a small angle below the flame. Instead of a charcoal support, they employ a wooden handle, upon which is fixed a flat disk of sheet-iron, about three or four inches diameter, covered with a matting of waste fragments of binding wire, entangled together and beaten into a sheet, about three-eighths or half an inch thick; some few of the larger pieces of wire, extend round the edge of the disk to attach the remainder. The work to be soldered is placed upon the wire, which becomes partially red-hot from the flame, and retains the heat somewhat as the charcoal, but without the inconveience of burning away, so that the broad level surface is always maintained. Small cinders arc frequently placed upon the tool, cither instead of, or upon the wire.

Sometimes, as in fig. 307, the gas pipe is surmounted by a square hood, open at both ends, and two blast pipes are directed through it; the latter arrangement is used by the makers of glass toys and seals; these are pinched in moulds something like bullet-moulds; the devices on the seals are produced by inserting in the moulds dried casts, made in plaster of Paris.

Makers of thermometers and other philosophical instruments, generally use a table blowpipe, with a shallow oval or rather a kidney-shaped lamp, fig. 308, with a loop placed lengthways upon the short diameter for holding the cotton, which is sometimes an inch long and half an inch wide. The wick is plentifully supplied with tallow or hog's lard, and a furrow is made through it with a wire to afford a free passage for the blast from the fixed nozzle, by the size of which, and its distance from the flame, the latter is made to assume the pointed or brush-like character. This lamp is more cleanly and emits less smell than those supplied with oil; any overflow of the tallow is caught in the outer vessel or tray, and when cold, the fat solidifies. The forge, fig. 90, page 203, has also a blowpipe and lamp to enable it to be applied to the arts in a similar manner, and a very cheap table blowpipe is described by Dr. Faraday, in his "Chemical Manipulation," page 120-169. See also Appendix, note G, p.462.

Many blowpipes have been invented for the enlployment of oxygen and hydrogen; the mixed gases were first used by Dr. Hare of Philadelphia, who has been followed in various ways by Clark, Gurney, Cumming, Hemming, Marcet, Leeson, and many others.* Two subsequent modifications of gas blowpipes which have been invented for the workshop, will alone be here described, namely, Sir John Robison's Workshop Blowpipe, intended for soldering, hardening, and other purposes;† and the Count de Richemont's Airo-hydrogen Blowpipe.‡

The general form of the "workshop blowpipe" is that of a tube open at the one end, and supported on trunnions in a wooden pedestal, so that it may be pointed vertically, horizontally, or at any angle as desired. Common street gas is supplied through the one hollow trunnion, and it escapes through an annular opening; whilst oxygen gas, or more usually common air, is admitted through the other trunnion which is also hollow, and is discharged in the center of the hydrogen through a central conical tube; the magnitude and intensity of the flame being determined by the relative quantities of gas and air, and by the greater or less protrusion of the inner cone, by which the annular space for the hydrogen is contracted in any required degree.

* The construction and management of nearly all the blow-pipes are described in Dr. Faraday's "Chemical Manipulation," 1830, pages 107 to 123. Also in "A Practical Treatise on the Use of the Blowpipe," by John Griffin. Glasgow, 1827.

† "The Workshop Blowpipe," which resembles a howitzer, is engraved and minutely described in the number of the Mechanic's Magazine for 2nd April, 1842.

‡ See the figure and description, Sect, v., page 454-6.

From amongst numerous other small applications of heat, Mr. Gill's portable blowpipe furnace may be noticed; it consists of a lump of pumice-stone three or four inches diameter, scooped out like a pan or crucible, and filled with small fragments of charcoal; sometimes a conical perforated cover is added; the inside may be intensely ignited, whilst the slow conducting power of the pumice-stone guards the hand from inconvenient heat.