VOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. ] 83 



the last of the quantity that did so, seemed to give the greatest flash, upon 

 which, the mercurial gauge descended something more than an inch, but 

 rose again -^ of the same. And on several repetitions of the like quantity 

 of powder (the factitious air being always first withdrawn) the phenomena 

 were very similar. Again, on purging the recipient of the factitious air, 

 and the mercury elevated in the gauge as at first, three quantities were 

 dropped on the iron, whose explosion, as well as the air produced from 

 them, seemed in proportion to the quantity of powder, the mercury then 

 in the gauge subsiding to 26. But upon dropping 6 quantities (the reci- 

 pient being purged as before) which quantities not descending at once, 

 but successively as fast as might be, the quantities that first reached the 

 still ignited iron taking fire, by their flame making an explosion of the 

 whole, at once blew up the recipient, although the weight of air incumbent 

 on it was equal to 144-|- lb. accounting the receiver at 3-^ inches diameter, 

 though it was something more, which sufficiently allows for the want of height 

 of mercury. The gauge then standing at 294^ instead of 30, from which the 

 calculation is made. The gunpowder used was the common glased sort, and the 

 weight of the six quantities, which removed the receiver, with so great a pres- 

 sure incumbent on it, was but 7 grains, each quantity weighing something more 

 than one. I did not observe the recipient to be broken before it reached the floor. 

 It was thickly lined with sulphureous and nitrous steams, so that the flashes of 

 fire through the cloudiness of the glass seemed very much to resemble faint 

 lightnings. The content of the receiver was equal to about 25-f oz. of water, 

 allowing for the bulk of the iron and pedestal. 



jin Experiment f made to try the Quality of Air produced from Gunpowder, fired 

 in Vacuo Boyliano. By Mr, Fr. Hauksbee. N° 295, p. I8O7. 



On making the late experiment of firing gunpowder in vacuo, it was hinted 

 as worthy of trial, whether the factitious air of fired gunpowder was endued 

 with any quality differing from common air : To satisfy the query, on Dec. 26, 

 about noon, I inclosed a red-hot iron in vacuo, the mercury in the gauge then 

 standing at 294^ inches; upon dropping the first quantity of powder, by which 

 is to be understood something more than a grain weight, its explosion made the 

 mercury in the gauge descend about an inch, undulating but very little. The 

 second quantity being let fall, the mercury subsided about 4 of an inch; and so 

 for several quantities following, it descended by pretty equal stages, till it had 

 fallen about 6 or 7 inches; and it was observed, that upon every quantity fired, 

 the undulations of the mercury increased. But after it had subsided 6 or 7 

 inches from 29-I, its several descents became less, little, if at all, exceeding 4. an 



