CamlitJIioi; of Phofphorifs in Vaaio. 237 



fubftance in a glafs veflel, after the manner of M. Lavoifier ; but not being able to avail 

 myfv-lf of the burning-glafs to fet fire to the phofphorus, I fuppofed 1 might fucceed by 

 electric fparks. I attempted therefore to give fire to the phofphorus by eleftrical fparks or 

 fmall difcharges. Neither of thefe being attended with fuccefs, I attached to a fmall piece 

 of phofphorus a little cotton fcarcely weighing three quarters of a grain, which I fprinkled 

 with a little finely powdered refin. I afterwards placed this cotton, whicli rofe about one- 

 fourth of an inch above the phofpliorus, in fuch a pofition between the extremities of tv.o 

 conducing wires vidthin the glafs receiver, that the eletlric fpark might pafs through it. 



In this manner, on the 4th of December 1794, I attempted for the firfl time the inflam- 

 mation and combuftion of phofphorus ; without any other defign, however, in this firit ex- 

 periment than to afcertain, before the le£lure, that there fliould be no fault in the appara- 

 tus or method of making the experiment ; and the time I could give on that day to this 

 experiitrent being already expired, I did not rarefy the air in the receiver, more than till the 

 mercury in the barometer gauge was about one inch lower than in the ftandard barometer 

 befide it. I then-pafled the oxygene gas from the gafometer into the receiver : I fet fire to 

 the phofphorus after the receiver was thus filled, and tlie experiment was madewithout any 

 difficulty. 



II. As I thought I could now repeat the experiment in my Ie£lure without any rilk of 

 failure, I made the attempt a few days afterwards. I placed another fmall piece of phof- 

 phorus in a fmall crucible of platina, which hung in the centre of a glafs receiver thirteen 

 inches in diameter, having firfl furrounded the upper part of the fmall (lick of phofphorus 

 with a little cotton powdered with refin. I then proceeded to rarefy the air as much as 

 poffiblc j but an unexpecled appearance prevented me. The candles had been removed, for 

 the better obfervation of the light at the furface of the phofphorus. We faw the light in- 

 creafe very perceptibly in magnitude and flrength, when the height of the mercury in the 

 barometric gauge Hill differed one inch from that in the barometer. This light increafed 

 in proportion as the air was more rarefied. I was far from fuppofing that the phofphorus 

 would take fire, for which reafon I continued to work the pump ; but, contrary to all 

 cxpe£lation, we faw the phofphorus take fire when the mercury was about half an inch 

 lower than that in the barometer. 



[To he cohthii/ed.2 



MATHEMATICAL CORRESPONDENCE. 



Question V. Anfivered by J. F n. 



X H F. bulk or volume of a chemical compound being very feldom, and perhaps never, 

 equal to the fum of thofc of its component parts before their union, it follows that the 

 relative quantities of its ingredients cannot be inferred from its fpccific gravity by the mere 

 rule of alligation; but rccourfe mull be had to the refiilts of adlual experiment. Perhaps 

 M. Baumt's experiments on the fpecific gravities of different folutions of common fait in 

 v/atcr, preparatory to the conflruflion of his pcf'--li(;ueur (an account of which will be found 

 in this work, p. 38.), with the appreciation of the fcale, deduceii from the obfervation of 

 M. Di; Morvcau, will afford us the beft data for the folution of the prefcnt qucftion. Th* 



fpccific 



