230 



PYROTECHNY. 



Pyrotech- pose of 'being assured that it can come out, must now 

 be introduced again to within about a diameter, or 

 somewhat more, of the extremity which it is intended 

 to choke. The subsidiary piece with its wire, which 

 was formerly mentioned, is then introduced at that end, 

 so that half a diameter may remain between it and the 

 former, which is occupied by the intermediate wire. 

 Being then placed within one turn of the pinching cord, 

 the lever is pressed down by the foot, and the case is 

 rolled backwards and forwards through the turn of the 

 cord, till the artist is satisfied that the wire is closely 

 -pinched. After this is done, a piece of strong twine is 

 wound round the furrow thus made, and secured by 

 three half hitches and some paste, or pasted paper or 

 glue. The ends of the case are then to be cut smooth 

 and even while it still lies on \he former ; and that 

 near the choke is to be cut in such a manner, that it 

 jmay have a hemispherical cup exactly equal to half a 

 diameter of the interior. The former and its piece 

 may then be withdrawn, that the artist may be satis- 

 -fied that the first of these is still loose, and the wet case 

 is then to be introduced into the driving mould on the 

 nipple only. By then restoring the former, and giving 

 two or -three slight blows to it, the mouth of the case is 

 rendered smooth and even. The spindle must then be 

 .passed through for the purpose of smoothing the vent 

 hole, and bringing it back to its proper size; or, if it is 

 a rocket case, the hollow rammer and spindle may be 

 .used at once, to give the whole of the parts about the 

 vent their true shape and size. 



There are some cases, such as those of tourbillons, 

 that require ta have both ends closed; and it is conve- 

 nient to close one of them, at least, in the choking en- 

 .gine. This is easily done by introducing a plug of 

 damp pasted paper, and then pinching the choking 

 rope close round it. Other cases, such as portfires, 

 .Roman candles, &c. that are to fire from an open mouth, 

 may be closed at the end in the same manner, as may 

 the cases for crackers and serpents. Such ends in the 

 larger works may be still farther secured by a coating 

 of clay driven on them within. 



The cases for illumination lights, or speckies, are 

 made of thin paper, rolled on formers, of diameters va- 

 rying from two to five-eighths of an inch, and their 

 lengths vary from two to six inches. These also are 

 pinched close at one end. Such cases only require 

 three or four rounds of paper, and the last one, at least, 

 -should be pasted. 



Portfire cases, as well for lighting fireworks as for 

 military service, must be made strong with pasted pa- 

 per, and the interior diameter, or that of the composi- 

 tion, may be about half an inch. The exterior one is 

 about six-eighths, and these cases must be from twenty 

 inches to two feet in length. The length of cases for 

 rockets, according to their several diameters, will be 

 found hereafter in the table of proportions for these ; 

 and, with respect to other fires, they will be more con- 

 veniently mentioned when these fireworks come under 

 review. 



It is sometimes convenient and ornamental that the 

 .cases of some fireworks should burn or -flame with the 

 re ; in others it produces a bad effect, or is hurtful. 

 In the fire wheels it adds to the ornament, by produc- 

 ing or increasing the interior white flame. In speckies 

 it isjnjurious, because the colour of the flame of the 

 paper .interferes .with that of the composition. In this 

 case, the paper should be impregnated with alum, by 

 which its flaming is prevented ; and this is -easily done 

 by soaking it in a saturated solution of that salt. 



Pyrotech- 



On the General Principles of Composition for Fireworks. \^^^^ 



- ... , . . . On the ce- 



IT will conduce to perspicuity to point out the gene- nei . a j T in . 



ral principles of the compositions which are used in ciples of 

 fireworks, as it will ako enable us hereafter to class composi- 

 them, in a great degree, in a certain order, according to tion for 

 their affinities and objects ; and thus to clear our essay, fireworks - 

 not only from the confusion that exists in all the com- 

 mon books on pyrotechny, but of many superfluous and 

 absurd receipts and repetitions of the same composition 

 under different names, in which they all abound. 



There are four principal objects in all the composi- 

 tions of -fireworks, under which some varieties are in- 

 cluded, and some of which are also necessarily com- 

 bined. The simplest requisite in these is explosion, or 

 the mere temporary 'blast, designed either for noise, or 

 for the purpose of throwing burning bodies to a dis- 

 tance, or, lastly, for conducting fire from one place to 

 another, through the parts of a simple or .complicated 

 piece. For all these purposes, the only composition is 

 common gunpowder, either entire or mealed, according 

 to the particular object that it is intended for. 



Next to this are those compositions which are re- 

 quired to produce motion, on the principle of recoil 

 and not of projection, where the piece, instead of the 

 ball, if we may use such an expression, i-s to be fired 

 away. The sky-rocket is the fir^t of these in which 

 the object is to produce the greatest possible recoil, con- 

 sistently with the safety of the piece itself; since, if 

 the charge were to go beyond this po ; nt, it would 

 burst. In the same class are serpents, together with 

 tourbillons, and the whole tribe of wheels, of whatever 

 construction these may be. For such works force is 

 required, although in different degrees, and therefore, 

 the compositions approximate in their nature to gun- 

 powder. In all of them, the basis is a mixture of salt- 

 petre, sulphur, and charcoal ; and- as far as mere mo- 

 tion is concerned, the objects are to be obtained by 

 this species of composition alone. Where the motion 

 is required to be most rapid, as in sky-rockets and 

 line-rockets, the proportions of the ingredients must 

 approach nearest to those used for gunpowder ; where 

 less so, as in some wheels, and other similar move- 

 ments, there the proportions depart more from that. 

 This is done by increasing the quantities of the sulphur 

 and the charcoal, or what is the same thing, by dimi- 

 nishing the proportion of nitre. At the same time, the 

 appearance of the fire may be altered while the force 

 continues the same ; as if!, while the proportion of nitre 

 remains the same, the sulphur chiefly is increased, the 

 effect will be to produce, more flame ; but if., on the 

 contrary, it is the charcoal which is augmented, red 

 sparks will predominate. 



Butj without materially changing the proportions of 

 these ingredients as used in gunpowder, the force of 

 explosion may be diminished by using an imperfect 

 mixture. Hence, when these three ingredients are 

 merely mixed in the way practised by artificers in fire- 

 works, instead of being ground together in the powder 

 mill, they will produce only a manageable recoil, when, 

 if they had been more perfectly united, they would 

 have exploded. In the same manner, the mere act of 

 condensation, by driving, will cause even the most 

 perfect gunpowder composition to burn slowly. 

 Coarseness of ingredients and imperfect mixture pro- 

 duce also, in these cases, another advantage ; as the 

 charcoal, which would otherwise give nothing but 

 flame, gives rise, in consequence of its imperfect pulve- 



