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FIRED GUN-POWDER. $1

q it passes through the hole R into the glass vessel, andpresses upon the surface & of the liquor contained init. This pressure makes the liquor rife suddenly inthe tube V W, after some undulations it fixes at aheight proportionate to the quantity of powder.

116. If the height of the water in the tube when theundulations cease be remarked, and the machine remain inthe fame state, it will be found on observing it, after equalintervals of time, that the water continues sinking; but lessafter the second interval than the first, and less after thethird than the second, till at length the alteration becomesimperceptible, except a very long interval be suffered toelapse. At the end of twenty-four hours, the liquor remainsstationary in the tube, affected like the thermometer, onlyby heat.

These undulations arise from the smoke of the sulphurand the caput mortuum of the powder, having absorbed apart of the elastic fluid: the absorption is considerable atfirst, but its effects gradually diminish. On comparing theheight of the water when it becomes stationary with itsheighth, when the undulations ceased, the difference willdenote the quantity absorbed by the smoke, &c. If the instantthe undulations cease, the communication between the upperand lower cavities be closed by the piston K, the water stopssuddenly, and never varies in height, unless affected by somealteration in the temperature of the atmosphere ; if, aftersome time, the communication be again opened, the waterwill suddenly sink in the tube, because the elastic fluid con -tamed in the lower cavity, rises to re-establish an equilibriumwith that in the upper one, a part of which has been ab-sorbed by the smoke and caput mortuum.

xi 7. It will not be amiss previous to the experiment,to make a few physical observations on the effects observedabove, and give some of the motives that influenced the par-ticular construction of the machine. When the quantityof powder consumed in the experiment is ^4^- of what theupper cavity could contain, if the cylinder E D E be takenoff when the machine is perfectly cool, the smoke and caputmortuum will be found attached to the upper part D D ofthe cylinder E D E, and to the upper part 12 of the othercylinder 10, 12, 10; the action of the fire will have changedthe colour of the latter, from its extremity 12, to about onethird of its length, while no mark of the Are or smoke ap-

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