The great heat raised from the blow-pipe has been a matter of surprise to many philosophers ; for it does not appear to act by increasing the combustion, as is the case in bellows applied to a furnace; it must therefore act by projecting the heat mechanically upon the object, with a greater force and velocity than when it receives it by the mere application of the flame. This opinion is founded upon some experim:nas made by Count Rumford, which will be found in vol. ii. of his Essays. The difficulty of managing the mouth blow-pipe, has induced many operators to employ the glass-blowers lamp. This is a table, with a pair of double bellows fixed beneath it, and worked by the foot. Upon the table, a lamp, or rather a dish of melted tallow, is placed, with a large cotton wick hanging Over the side of it. The flame of this is blown by a nose-pipe fixed above the table, and ha ving universal motion. This machine is extremely useful in many of the arts, for softening and bending glass tubes, and for forming any small vessels in glass; and, indeed, it is by this means that all small glasses are blown, as we shall describe tinder GLASS Blowing. This instrument is not at all convenient for the pur pose of experiments, as the motion of the body caused by blowing with the foot, prevents the object from being held with the requisite steadiness; though it is extremely useful to the artist fur soldering small things in metal, hardening small drills, enamelling, and many other purposes.
In order to have an apparatus at once convenient, steady, .and powerful, the alcohol blow-pipes have been invented. Two of these are represented in Plate LXII.
The first, Fig. 7. is the invention of Professor Pictet of Geneva, and consists of an oval vessel AB, filled with oil, and having two wicks at C and D. The former is for the flame, which is to be blown, and the other is smaller, being intended to heat a small boiler E, which is filled with spirits of wine. On the top of this boiler, a syphon tube F is screwed, which turns down, and presents its jet c to the flame of the wick C. The boiler is fitted into a ring, which is supported by a collar sliding up and down on a wire G, and can be fastened by a screw S at any elevation. The nose can be moved sidewise on its wire to meet the flame ; and its distance from the flame may be varied, by turning the socket of the wick round. The not being in the centre of the socket, of course traverses in a small circle. The jet unscrews it c, to change it for a larger or smaller aperture. This blow-pipe operates by the alcoliol being boiled by the heat of the lamp D, and its steam or vapour passing over through the syphon tube to the flame at C. Its advantages are, steadiness of the flame, and, at the same time, the inflammable vapour very greatly increases the effect. The only objection to it is, the expense of alcohol and the two lamps.
Fig. 8. is another form of the same instrument, proposed by Mr Benj. Hook. Here the boiler is a globe B, supported in a ring fixed on two pillars aa. Between these, a small lamp E slides up and down, and is retained at any height, by the friction of two small springs. This lamp at the same time heats. the boiler B, and its flame is urged by the vapour which issues at a pipe F. This passes through the boiler, and rises np above the surface of the spirit, so that there is no danger of its boiling over into the tube. At G is a valve, loaded with a weight acting as a safety valve, to permit the escape of the vapour, if it should become so strong as to endanger the rupture of the vessel ; and at H is a screw plug, through which the alcohol is introduced. This instrument acts in the
same manner as that before described ; and the ad justment of the distance of the wick from the jet is affected in the same manner. The alcohol blow pipes arc not a new invention, one being- described by the Abbe Nollet, in his Art des Experiences, published in 1770. They have, however, but lately been brought into use, and are found to answer ex tremely well for small experiments, where the con sumption of alcohol is not serious.
From what we have already said, our readers will form some idea of the requisites for a good blow pipe ; and weibeg to present them with one, con structed on the same plan as the great blowing en gines for the iron furnaces. It is represented in Fig. 9. of Plate LXII. where AB is a vessel of ja panned tin, or glass, containing water, and C another included within the former, and closed by a dome at top, and open at the bottom. It is supported in the other vessel by a ring or cover, soldered to both, and perforated with several holes, as shewn in the Figure. On the top of the dome, a short brass tube is soldered, the outside of which is made conical, for the reception of a socket, projecting from the side of a common blow-pipe D. The mouth-piece of this blow-pipe is made globular at tr, and a short tube b is fitted into it, with a valve adapted to the end of it, -shutting outwards, so as to prevent the return of any air into the mouth. At the other end of the blow .pipe, a curved tube d is fitted on, which has the jet at the end of it. The lamp B is situated on the top of a pedestal, and can be raised or lowered at pleasure, by means of the rivetted nut F. This nut fits upon a screw formed on the stem of the lamp, the lower part of which stem is made square, to prevent it turn ing round by the action of the nut. The vessel makes a steady support for blow-pipes, which is used by applying the mouth to the tube b, and throwing air into the interior vessel C ; this expels the water at the lower end of it into the external vessel ; and the pressure of the water to return to its original level, causes a constant compression of the air, and forces it through the jet into the flame of the lamp. By this means it is not necessary to blow constantly with the mouth ; for if the air is forced into the receiver at intervals, the pressure of the wa ter will expel it in a constant stream, and the opera tor will not be fatigued by any of the causes above enumerated ; or lie may take his mouth from the pipe at any time for a few seconds, without interrupt ing the stream ; and lie may take the air into his mouth, and blow it into the tube, so as to supply it with pure atmospheric air, instead of that which has passed into the lungs : or if it is more convenient, he may employ an assistant to blow. The socket which con nects the blow-pipe with the dome C, is made coni cal, and fits on very stiff, so as to fix the blowpipe very firm, at the same time that it admits the pipe to have an angular To adjust its distance from the frame, the joint connecting the jet d with the pipe, is fitted in the same manner, to admit of changing the elevation of the jet ; and a jet of any other form or size may be fitted on at the same joint. It will easily be seen, that this blow-pipe may be adapted to blow with oxygen gas, by connecting a flexible tube with the mouth-piece b. The gas is injected into this pipe • from a bladder filled with gas, by means well known to chemists.