PYROTECHNY. 



Table f. — Size of the Calibre of Moulds of a Pound 

 Weight and below, to One Ounce. 



Here it is evident, that the mould of a rocket of twelve 

 ounces in weight ought to be feventeen lines in diameter ; one 

 of five ounces will require a mould of thirteen lines in diameter. 

 Hence we derive an eafy method of finding the fize when 

 the weights are given : and if the diameter of the rocket be 

 given, it will be equally eafy to find the weight of the ball 

 correfponding to that calibre. Thus, if the diameter be 

 fifteen lines, it will, by the table, be feen that it cor- 

 refponds to a ball of eight ounces. 



Table II. — Size of the Calibre of Moulds, of from 

 I to a 50lb. Ball. 



By this fecond table, if the weight of the ball be given 

 the fize of the mould may be found: fuppofe it be 18 

 pounds, oppofite to it is the number 262. Then we fay by 

 the rule of proportion (as igi, fee table I. is fuppofed to 

 be divided into 100 parts), 100 : ig-l :: 262 to the fourth 

 term fought, viz. 51-09 ; therefore the required calibre is 

 J2 lines nearly, or four inches and four lines, or 4]^ inches. 

 But if tlie calibre be given in lines, the weight of the ball 

 may be found : fuppofe the given calibre be 36 lines, then 

 as 19I : 100 :: 36 : 184. The neareft number in the table 

 to this is 181, which (hews that the weight of the ball will 

 be rather more than 61bs., or, in other words, that a rocket, 

 the diameter or calibre of which is 36 lines, is a rocket of a 

 61b. ball. 



The compofition of the powder for rockets mufl be 

 different, according to the different fizes, it being com- 

 pletely afcertained that what is proper for fmall rockets 

 would be too ftrong for the larger ones. 



For rockets of one or two ounces, the compofition fhould 

 be one pound of gunpowder, and two ounces of finely ground 

 foft charcoal. 



For rockets of fomewhat larger fize, the compofition may 

 be ten ounces of gunpowder, three and a halt of faltpetre, 

 and tliree ounces of charcoal. 



If the rockets be of five or fix ounces weight, then to two 

 pounds five ounces of gunpowder, add eight ounces of falt- 

 petre, two ounces of fulphur, fix ounces of charcoal, and 

 two ounces of iron filings. 



If the rockets be from ten to twelve ounces, you may 

 add to feveateen ounces of gunpowder, four ounces of falt- 

 petre, three and a half of fulphur, and one of charcoal. 



For rockets of a pound weight : to one pound of gun- 

 powder add an ounce of fulphur, and tliree ounces of 

 charcoal. 



For rockets of from four to feven pounds : to thirty-one 

 pounds of faltpetre, add four pounds and a half of fulphur, 

 and ten of charcoal : and for thofe that are ftill larger, we 

 may add to eight pounds of faltpetre, one pound four ounces 

 of fulphur, and two pounds twelve ounces of charcoal. In 

 all cafes the ingredients are to be pounded feparately, and 

 finely flfted before they are ufed. Gunpowder, thus reduced 

 from the corns in which it is manufactured, is called meal- 

 powder. 



Matches. — The matches to let off rockets are thus made. 

 Take linen, hemp, or cotton thread, and double it eight or 

 ten times, if intended for large rockets, or only four or five 

 times, if to be employed for liars. When the match is thus 

 made, dip it in pure water, and being foaked, it is to be 

 fqueezed as dry as poffible. Mix fome gunpowder with a 

 little water, fo as to reduce it to a kind of pafte, and im- 

 merfe the match in it, turning and twilling it till it has im- 

 bibed a fufBcient quantity of gunpowder ; then fprinkle it 

 over with dry powder, and when it is dry, it is fit for ufe. 



In anfwer to the inquiry what caufes rockets to afcend in 

 the air, we may obferve, that it is nearly the fame as that 

 which produces a recoil in fire-arms. Thus, when powder 

 is inflamed in the chamber of a mufket or cannon, it exerts 

 its power again ft the breech of the piece, and againft the 

 bullet or wadding. But the refiftance oppofed by the 

 bullet being much lefs than that oppofed by the mafs of 

 the barrel or cannon, the bullet is forced out with great 

 velocity. Tlie caufe of the afcent of a rocket is nearly the 

 fame. At the moment when the powder begins to inflame, 

 its expanfion produces a torrent ot elailic fluid, which afts 

 in every direftion, that is, againfl the air which oppofes its 

 efcape from the cartridge, and againft the upper part of the 

 rocket ; but the refiftance of the air is more confiderable 

 than the weight of the rocket ; therefore the rocket afcends 

 by the excefs of the one of thefe forces over the other. 

 This, however, would not be the cafe unlefs the rockets 

 were pierced to a certain depth. 



BriUiant Fire and Chinefe Fire As iron-filings, when 



thrown into the fire, enflame and emit a fl:rong light, this 

 gave rife to the idea of rendering the fire of rockets much 

 more brilliant, than when gunpowder, or the fubftances of 

 which it is compofed, are alone employed. But the Chinefe 

 have long been in pofltffion of a method of rendering this 

 fire much more brilliant and variegated in its colours. It 

 confifts in the ufe of a very fimple ingredient, namely, cafl 

 iron reduced to a pt-wder more or lefs fine : the Chinefe 

 give it a name that anfwers to iron-fand m our language. 

 It is prepared from old iron pots pulverized, till the grains 

 are not larger than radifh feed. Thefe, however, are 

 pafFed through fieves of different degrees of fiiienefs ; thofe 

 that pafs through the clofeft fieve, are called fand of the firll 



order ; 



