On the prefent State of Airoflatlon. 23 



lowed by the extrication of a large quantity of hydrogen gas 

 from the dccompofnion of the water; but the metal is apt to 

 run to a (lag refembling finery cinder, preventing its further- 

 aition upon the water, and that before anv confiderable pro-' 

 portion is deconipofed. 



The diftillation of pit-coal alfo affords this gas, but not 

 above one-fourth hghter than atmofpheric air. In obtaining 

 it in this way, a number of receivers mufi; be interpofed be- 

 tween the retort and the balloon, to condenfe the volatile, 

 aqueous, and oleaiiinous produfts of this dillillalion *. 



If a parachute is required, it fliould be conftrufted fo as 

 when diftended to form but a hnall fegnient of a fphcre, and 

 not a complete hemifphere; as the weight of this machine 

 is otherwife confiderably increafed, without gaining much 

 in the oppofing furface. The parachute of Mr. Garnerin is 

 particularly defective in a too great extenfion of its diameter ; 

 an unneceilarv addition to its weight of a lining of paper both 

 withinfide and without ; the too near approximation of the 

 baflcet to the body of the parachute; and efpecially in the 

 want of a perpendicular cord paffing from the car to the centre 

 of the concave of the umbrella, by the abfcnce of which 

 the velocity of the defcent i» certain to be very rapid before 

 the machine becomes at all dillendcd; whereas, if a cord were 

 thus difpofed, the centre of the parachute would be the por- 

 tion firft drawn downwards by the appended weight, and the 

 machine would be almoft immediately at its full extenfion. 



Having found, by experiment, the diameter required for 

 infnring fafetyf, the further the bafket or car is from the 

 umbrella, the lefs fear (hall we have of an inverfion of the 

 whole from violent ofcillations ; yet the longer the fpace be- 

 tween the car a^id the head of the machine, tiie longer will 

 be the fpace run through in each vibration when once begun, 

 yet by fo much the more will they be fteadier; and this 

 ought to be attended to, as when by the violence of the ofcil-r 



* During the diftillation of pit-coal, water and carbonr.te of ammonia 

 arc artbrded, tos^ether witii a piithy oil refembling tar i thefe will be con- 

 denfed in ihe ne^rcft receivers, while the galjcqus produdt (confiliiog of ^ 

 mixture of hydrogen with azotjc mid c;u-bonic acid gafes) will proceed on- 

 ward; and which if made to pafs through lin.e-water will be rendered 

 more pure: a pound of coal will afford about three cubic feet of intlam- 

 niable a'r, and prove the cheapell metliod of inflation. Dr. Prieftley alfo 

 found that the produ6Vof inflammable air, in ail ojierat'ons in the dry way, 

 was alwavk greater in proportion as the fire li'ad been Aiddenly raiied, 



t Mr. Bdkiwin advifes the di,.ineter 15 feit; by which mtans, " the 

 man weighing 140 pounds and the panichuto 13 pounds, v.itli a (ui face of 

 150 fquarc feet, he would feti no greater Ihock tlian if he had fallen from 

 the height of fix feef." At the Pantheon, Mr. Garnerin's parachute was 

 anneuuced its being ^ofttt in diameter, and weighing abo\e ho pmuuis. 



C 4 luiious 



