Ciiniu/Hoit cf Gtmpoiuder in a Ckfed Vejfel. 46 1 



the method was abandoned. It was found almofl impoffible to prevent the efcape of the 

 elaftic fluid by the fides of the pifton; and the rcfults of apparently fimilar experiments were 

 exceedingly different, and fo uncertain, that the Count was often at a lofs to conje£lure the 

 reafons of thefe extraordinary variations. 



In order to elucidate thefe in a difcurfive way, the Count proceeds to remark, that Mr. 

 Robins's two affumed pofitions, namely, that the operation of gun-powder is performed by 

 the rarefa£lion of a permanently elaftic fluid, and that the whole of any charge is fet on 

 fire before the ball Is fenfibly moved from its place, are not to be admitted. On the con- 

 trary, from his own experiments, the Count is difpofed to refer the prodigious expanfion of 

 fired gun-powder to the a£lion of water in the (late of lleam at a very elevated temperature; 

 and he fliews by various obfcrvations, feveral of which mud be familiar to every one who 

 is habituated to ufe this agent, that the accenfion of gun-powder is fo far from being per- 

 formed in an extremely minute portion of time, that it is in every inftance gradual and 

 progreffive. But having found it impoflible to meafure the elaftic force of fired gun- 

 powder with any degree of precifion by the methods already mentioned, he totally changed 

 hjs plan of operations, and, inftead of endeavouring to determine its force by caufing the 

 generated elaftic fluid to aft upon a moveable body through a determinate fpace, he con- 

 "Iriyed an apparatus in which this fluid was made to a£l by a detertnlnate furface againft a 

 weight, which being increafed at pleafure (hould at laft be fuch as would be juft able to 

 confine it, and in that cafe would juft counterbalance, and confequently meafure its elaftic 

 force. 



A folid block of very hard ftone, four feet four inches fquare, was placed upon a bed of 

 folid mafonry, which defcended fix feet below the furface of the earth. Upon this block of 

 ftone, which ferved as a bafe to the whole machinery, was placed the barrel in which the 

 explofions were made. It was made of hammered iron 2,78 inches long, and 2,82 inches 

 in diameter at its lower extremity, which was flat in order to reft upon its fupporter. Its 

 bore was one quarter of an inch in diameter, 2,13 inches long, meafured from the upper fur- 

 face of the barrel, and it ended in a very narrow opening below, not, more than 0,07 of an 

 inch in diameter, and 1,715 inch long, which formed the vent or paffage by which the fire is 

 communicated to the charge. Thispaflage, however, was not open below, but terminated in 

 a projection from the centre of the bottom of the barrel about 0,45 of an inch in diameter, 

 and J, 3 inch long, which formed the vent tube clofed below. When this baiTel is placed 

 upon its ftand, which is of gun metal, the vent tube paffes, through a hole, into a 

 cavity in the ftand which has a lateral opening. Lito this lateral opening a ball of red hot 

 iron is introduced, having ar proper cavity witliin for the reception of the vent tube, which 

 it fpeedily ignites, and fets fire to the powder through the folid fubftance of the tube Itfelf. 

 The opening of the bore of the barrel, which is placed in the vertical pofition when in ufe, 

 is clofed by a folid hemifphere of hardened fteel, whcfe diameter was 1,16 inch, its plain 

 Cde being downwards, h is confined laterally by three upright cylindrical pins, which 

 allow it to rife only in the vertical direiSlion. Upon this hemifphere is placed the weight 

 made ufe of for confining the elaftic fluid generated from the powder in its combuftion. 

 This weight,which in fomc of the experiments was a heavy twenty-four pounder placed ver- 

 tically upon its cafcabel, being fixed to certain timbers, was capable ot Aiding up and down 



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