This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The blowpipe and an alcohol lamp are largely used in hard soldering, tempering small tools, and by chemists and mineralogists as an important means of analysis, etc, and for these uses the blowpipe has received very great attention, both from mechanics and distinguished philosophers. Most of the small blowpipes are supplied with air from the lungs of the operator, and the larger ones, or where they are brought into general use, are supplied with air from a bellows moved with the foot, or from a vessel in which the air has been condensed by a syringe, or from a small rotary fan. The ordinary blowpipe is a light brass or tin tube about 10 or 12 in. long, and 1/2 to 1/4 in. in diameter at the end for the mouth and 1/16 in. or less at the jet end. The small end is slightly curved, so that the flame may be thrown immediately under the observation of the operator. There are several other kinds of blowpipe for the mouth, which are fitted with various contrivances, such as a series of apertures of different diameters, joints for portability and for placing the jet at different angles, and with a ball for collecting the condensed vapour from the lungs; but none of these is in common use.
The blowpipe may be supplied with air from the lungs with much more effect than might be expected, and, with a little practice, a constant stream can be maintained for several minutes if the cheeks of the operator are kept fully distended with wind, so that their elasticity alone will serve to impel a part of the air, while the ordinary breathing is carried on through the nostrils for a fresh supply.
The heat created by the blowpipe is so intense that fragments of almost all the metals may be melted when they are supported upon charcoal, with the heat from a common tallow or wax candle. The most intense heat from the blowpipe is the pointed flame, and the hottest part of the flame is the extreme point of the inner or blue flame. Large particles of ore or metals that require less heat are held somewhat nearer to the candle or lamp, so as to receive a greater portion of the flame, and when a very mild degree of heat is wanted on a small piece of metal it is held farther away. By thus increasing or decreasing the distance between the candle or lamp and the object to be melted, any desirable degree of heat may be obtained. When only a minute portion of metal is to be heated, the pointed flame is used with a mild blast; but when it is desirable to heat a large surface of metal, as in soldering and brazing, a much larger flame is used. This is produced by using a lamp with a large wick, plentifully supplied with oil, which produces a large flame.
The blowpipe used has a larger opening than the one employed for the pointed flame, and is held at a little distance from the flame and blown vigorously, so as to spread it out over a large surface of the work, This is called the bush or sheet flame. The work to be brazed or soldered by this flame is generally supported upon charcoal.
When melting metals with the blowpipe, the metal to be melted is laid upon a flat piece of charcoal, which has previously been scooped out slighly hollow in the centre to prevent the metal from running off when melted. If it is desirable to run the metal into a mould when melted, a small groove or lip is cut in the charcoal, and when the metal is sufficiently heated it is poured into the mould. In this way, jewellers melt most of their gold, silver, etc, when making rings and other jewellery. The cupel is also used for melting metals in with the blowpipe, but it is not so good as the charcoal, for it is liable to break from being heated unevenly, and spill the metals. Several different kinds of stationary or bench blowpipes are used by jewellers, braziers, etc.
Two examples of the mouth blowpipe are shown in Fig. 152, the form a having a movable nozzle which may be screwed on and off, thus admitting of the use of a jet with the most suitable sized orifice. The flange b is convenient for holding the blowpipe in the mouth.
Lamps or their equivalents show a variety of forms. The most primitive yet efficient method of obtaining a flame is to tie a bundle of dry reeds, coated with tallow by immersion in melted suet, in a paper wrapper, and stick it in a hole in a piece of wood, as in Fig. 153. Spirit lamps differ according to the material burned in them and the degree of heat required from them. A handy little lamp for delicate objects is shown in Fig. 154. One made by Griffin for burning a mixture of wood spirit and turpentine (4 volumes to 1) is illustrated in Fig. 155. Fletcher's lamp (Fig. 156) for the same mixture has the spout made large enough to accommodate 5 or 6 folds of 1-in. soft cotton wick. All these lamps should be capped when not in use. Figs. 157 and 158 represent respectively the fixed and adjustable forms of the patent self-acting soldering lamps with blowpipes attached. Fig. 159 is a Bunsen gas-burner.