CATALOGUE. — PNEUMATIC MACHINES. 



£61 



Two ounces of powder impelled a ball of 28| oz. with a 

 Telocity of 013 feet in a second : this would carry it to a 

 height of 5930 feet, producing an effect equal to the labour 

 of a man continued 105 seconds, and 10 hours of such la- 

 bour would produce an effect equal to that of 43 pounds of 

 powder. This force is therefore not comparatively cheap, 

 lupposing the whole effort of the powder to be consumed : 

 but it would be almost impossible to find mechanical means 

 •o convenient for producing velocity. Air, compressed in 

 ah air gun, would never move even into a vacuum with a 

 velocity greater than about 1400 feet in a second : much 

 less could it carry before it the weight of a cannon ball 

 with a velocity of 2000 feet : and a bow or a spring of any 

 kind would have a still greater disadvantage. The great 

 rarity of the heated elastic fluids disengaged from powder, 

 combined with their great elasticity, gives them the faculty 

 of imparting so prodigious a velocity. Hydrogen gas, suffi- 

 ciently condensed, would escape with a velocity 3 times as 

 great as common air. Hutton thinks the force equal to 

 1500 or 1600 atmospheres. Y. 



Ingenliousz. Ph. tr. 1779. 



Robins found the force of gunpowder equal to 1000 at- 

 mospheres, and observed, that a red heat made air expand to 

 4 times its bulk; hence he inferred that powder produced 

 450 times its bulk of air. Hauksbee, Amontons, Belidor, 

 and Saluces agree that it yields 322 times its bulk. 



Thompson's e.^periments on gunpowder. Ph. 

 tr. 1781. '4J29. 



Count Rumford observes, that the piece is heated sooner 

 when fired without than with balls, perhaps because the 

 great velocity of the air excites more heat by friction. When 

 the piece is become warm, a smaller quantity of powder 

 serves. The operation of ramming increases the force of 

 powder in the ratio of 6 to 5, or more : the velocity is nearly 

 in the subduplicate ratio of the weight of the powder, at 

 least for musket bullets. The situation of the vent has very 

 little effect ; the cavity of the piece should have a hemi- 

 ■pherical terminarion. The Telocity is more accurately de- 

 termined by measuring the recoil of the piece when sus- 

 pended than by the motion of a pendulum struck by the 

 ball, deducting always that which would be produced 

 without any ball. The velocity was sometimes greater 

 than 2000 feet in a second. Robins makes the force 

 of gunpowder equal to looo atmospheres ; but, upon 

 his own principles, it is equal at least to 1308. The 

 velocity is very nearly in the subtriplicate ratio of the weight 

 of the -ball, increased by half that of the powder, inversely. 

 The force of aurum fulminans appears ts be but one fourth 

 •f that of gunpowder. The experiments were made with a 



bore of about f inch. It is surprising that there should be 

 so much difference between these experiments and others, 

 that a quadraple weigh; in the one case should have pro- 

 duced the same effect with an octuple weight in the other. 

 It may be questionel whether the difference of the squares 

 of the velocities ought not rather to be taken in making the 

 correction for the recoil. Y. 



Rumford on the force of fired gunpowder. 

 Ph.tr. 1797. 222. Nich. I. 439. Gilb. IV. 



257, 377. 



Bernoulli makes the expansive force of gunpowder equal 

 to 1 000 atmospheres ; Rumford, from the bursting of a 

 barrel of iron, so 000, from some more direct experiment!, 

 from 20 000 to 40 000. The utmost that can be justly in- 

 ferred from the bunting of the barrel is in reality about 

 30 000, since the tension could by no means be equal 

 through every part of its substance. The force was, in at- 



1 + .4X 

 mospheres 1.841 (looox) x being the quantity of 



powder, the whole capacity of the cavity being unity. In 

 some other experiments the multiplier, instead of 1.841, ap- 

 pears to be 6.37; giving 101021 atmospheres instead of 

 29 178, when X becomes 1. A cubic inch of gunpowder 

 contains nearly 11 grains of water of crystallization, and j, 

 of moisture, which Count Rumford thinks, would be suffi- 

 cient for furnishing the steam. This is however a great 

 mistake : a heat of 1200 would scarcely more than double, 

 or at most quadruple, the expansive force of a given portion 

 of steam, consequently the density of steam at this temper- 

 amre, exerting a pressure of 50 000 atmospheres, ought to be 

 more than 1 000 times as great as under the usual pressure, 

 that is, probably, almost 4 times as great as the density of 

 water. Count Rumford finds that much of the powder it 

 discharged unfired. 



E. M. A. VI. Art. Poudre a canon. 



Massey on saltpetre. Mauch. M. I. 184. Rep. 



I. 248. 

 S. E. XI. 



A collection of memoirs on saltpetre. At first there were 

 38 unsuccessful attempts ; in the second instance Thouve- 

 nel gained the first prize of 8000 livres, among 28 competi- 

 tors. A few of the best memoirs only are printed at large. 



Napier on gunpowder. Ir. tr. 1788. II. 97. 

 Rep. II. 276. 



Robison. Enc. Br. Art. Projectiles, Resist- 

 ance. 



Bullion on saltpetre and gunpowder. Repert. 

 VI. 49. 



