Fig. 5. is a convenient blow-pipe. Its ivory mouth-piece a, is fitted to the end of a brass tube A ; and at the other end of this is soldered a small cylindrical box B, from the centre of which the jet b proceeds. This is fitted in by a joint, which al lows the jet to be placed at any angle with the tube, a property which will frequently be found conve nient to placing the flame in any direction. The joint is formed by a part of the jet, at right angles to the nose b, being fitted through a hole in the box; and the end, which comes through, rivetted down, at least so far as to prevent it coming out The box B has a lid c, which unscrews for the purpose of wiping out the dampness.
Fig. 4. is Dr Wollaston's ingenious portable blow pipe, which is remarkable for its neatness, and the small space into which it may be packed. A is the mouth-piece, b a second length of the tube, receiving the conical end of the first, and•d the jet, with a small globe e, which has a hole through it to. admit the end of b. In the side of this is a hole, which, when the two are put together, coincides with the tube of the jet d. This pipe, when joined, has only the pro perties of the common blow-pipe before mentioned.. When its parts are separated, as in the figure,- the jet e is thrust into the-large end of b, but•the globe is left projecting out of the end; then both these are pushed into the tube A, at its large end, by which means, when put up, it is only the size of A, which is not larger than a small pencil, and may be always carried in the mineralogist's pocketbook; and in many instances will prove extremely useful when a better pipe is not at hand.
Fig. 3. is a blow-pipe, which has been handed to us by its inventor. It consists of two tubes A, B, of a tolerable size, soldered togetherlike a hammer.. The jets are screwed in at a, and the end of them projects some distance into the tube B, in order to prevent the water from being blown out. The jet, b, at the opposite end, is for the escape of a part of the air. When blowing with a small jet, the quan tity of hir required is so small, that the operator would find relief in opening another, as he would then be enabled to breathe more frequently, and with greater ease.
It will readily be seen, that all the blow-pipes above described have advantages peculiar to them selves, though the differences between them are but trifling ; and any of them will perform well, if sup plied with a constant-and equable stream of air, in which lies the principal art of ,using the blow-pipe. This is effected by the operator breathing freely through his nostrils, in the most natural manner, without breathing materially quicker or slower than ordinary ; but at every expiration, throwing a por tion of air into the mouth, so as to inflate the cheeks,. which, by their muscular action, condense the air, and force it through the tube into the flame, in a continued stream, though the mouth is only supplied. at the interval of every respiration. To perform this readily, requires some practice; and the facility of it can only be obtained by habit, it being one of those things which is not easily taught by words. If a person finds any difficulty in the first attempt, he will derive some advantage, from accustoming him. self to breathe through the nostrils, first with the mouth open, and then shut • for in either of these cases, the passage from the flings through the mouth is closed. Having acquired this habit, he should begin to throw some of the air at each expiration into the mouth, as above to ; suffering it to escape regularly through to the pipe, or any other tube held in the lips : but it should have a aperture than the jet of the blow-pipe,. to render the Pe. operation more easy; andIe mat endeavour to com '' press the air by the cheeks, with an equable force ; • for the regularity of the blast materially depends on the regular pressure of the air. Every time, therefore,
that the air is injected into the mouth, the cheeks will be swelled out by suffering the muscles to relax in some degree, to enlarge the capacity of the mouth, and will gradually subside as the air issues forth, till a fresh supply inflates them. By this means the mouth will exactly imitate the action of the upper portion of a pair of smiths' bellows, and will regulate the blast on the same principle. The most effective ap plication of the blast to the flame, is the next object of consideration. A lamp is sometimes used, but a candle is probably better. In either case, the flame which it raises must be considerable. The end pipe must be just entered into the flame, and the current of air will throw out a horizontal cone of flame from the opposite side. If it is well managed, the cone will be as distinct and well defined as possible, and extending often to the length of three inches. Care must be taken that the stream of air does not strike against any part of the wick,. as it would then be divided, and the cone split into several. It is for this reason that a large flame is required, because the pipe must be somewhat above the wick ; and -unless the flame is considerable, there will not be sufficient at that part for the stream of air to act upon. In order to. increase the flame, it is proper to allow the •candle to burn till it has a considerable length of snuff ; and ihis should be opened out into numerous heads, or the wick turned down, so as to expose the largest surface, and cause the greatest flame. The pipe should then be through that part of the flame where the combustion appears toile the most perfect and brilliant. By examining the horizontal cone of flame, it 'appears to formed of two, the interior cone being blue, and the external yellow, which is therefore the longest, and terminates the flame : the blue being so much deeper in colour, gives the base of the cone the appearance of being blue and capped with. yellow. The subject of expe riment is held in the yellow flame till it becomes red hot, and is then advanced towards the candle, to bring it into the blue flame, where it receives the greatest heat. It is held in the small .platiiia spoon, Fig. 6, which has the advantage of reflecting the flame from all sides upon the object ; and though this does not perhaps actually increase the heat thrown upon the object, it creates an atmosphere of flame and heated air around it, which prevents the object being so much cooled, if it should for an instant .be moved out of the cone flame, from the unsteadiness of the hand in holding the pipe or the spoon, or from acci dental currents of air which would disthrb the flame, and cause such a wavering in the point of the cone; as to divert it, in 'Some measure, from the object. • The most expert operators with the blowpipe find, that after they have attained the art of blowing with the most perfect regularity, they sometimes fail in the course of a long experiment, by a tremulous motion which seizes the lips, from the fatigue of holding the pipe so long, with a sufficient force, to prevent the escape of the air by the sides of it. This causes such a motion of the pipe, ,that the flame is too unsteady to produce a proper effect upon the ob ject. When charcoal is used to support the subject of experiment, it should be of a close compact grain, and properly burnt ; for if it is too little carbonised, it will flame like a piece of wood, and obscure the object ; and if it is too much burnt, it is so quickly consumed and burned to ashes, that the object is in danger of being lost in it. The charcoal greatly in creases the heat ; but we are disposed to think that this arises more from the cause to which we have as cribed it in the case of the platina spoon, than from its own combustion, though this has doubtless some effect in heating the object at the opposite side.