614 



BLOW-PIPE. 



Blow- pipe. O p era tion more easy; aaoVae mult endeavour to cora- 

 "' ~ press the air by the checks, 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 this should be opened out into 

 numerous heads, or the wick turned down, so as to 

 ' xpose the largest surface, and cause the greatest 

 flame. The pipe should then be directed through 

 that part of the flame where the combustion appears 

 to be the most perfect and brilliant. By examining 

 the horizontal cone of flame, it appears to be 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 platina 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 disturb 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 blow-pipe 

 and, 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 

 . rauses such a motion of the pipe, that the flame is 



I'l.AT 



1.XII. 



too unsteady to produce a proper effect upon the ob- Bfow-pipr. 

 ject. When charcoal is used to support the subject > v ' 

 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. 



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 experiments made 

 by Count Rumforo, which will be founa 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 under 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 for 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'* 

 Pictet of Geneva, and consists of an oval vessel AB, alcohol 

 filled with oil, and having two wicks at C and D. blow-pipr 

 The former is for the flame, which is to be blown, }'i^T E 

 and the other is smaller, being intended to heat a p; e . 7, 

 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 e 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 wick not being in the centre of 

 the socket, of course traverses in a small circle. The 

 jet unscrews at e , to change it for a larger or smaller 

 aperture. This blow-pipe operates by the alcohol 

 being boiled bv the heat of the lamp D, and its steam 



3 



