a3» Combiipkn of Phfphoriis in thi Vaeiium of tht Air Pump. 



I then thought there was fome rcafon to fuppofe that the refin might be the caufc of the 

 inflammation ; and to determine this point, I put under the fame receiver three fimilar fmall 

 flicks of phofphorus, one of them fimpiy powdered with refin, another wrapped in cotton 

 •without refin, and the third wrapped in cotton powdered with refin, in the fame manner as 

 in the former experiments. The light began to increafe at the fame time in all three, 

 namely, as foon as the mercury had fallen to about one inch in the barometer. The phof- 

 phorus wrapped in cottorLpowdered with refin took fire firfl ; a fliort time afterwards that 

 ■which was wrapped fimpiy in cotton took fire; and that alone which was fimpiy powdered 

 with refin did not take fire at all. 



V. After thefe refults, the queftion was, to know in what manner the cotton could caufc 

 inflammation in air fo rarefied, in which every other combuftible, though fet on fire, would 

 ceafe to burn j and dill farther, how phofphorus could fpontaneoufly take fire when the 

 experiment was made in an atmofphere where the temperature docs not exceed 56 or 58 

 degrees of Fahrenheit, though the phofphorus does not take fire in the open air unlcfs 

 heated to about 112 degrees of Fahrenheit. After fome reflexions and experiments, 

 I found that this fingular phenomenon could be very eafily explained according to 

 ihe principles of the modern chemiftry. The increafe of the light which precedes the in- 

 flammation when the air is rarefied to a certain degree, fuggcfled to me this explanation- 

 I fliall therefore, in the firft place, explain the evident caufe of the increafe of light in the 

 phofphorus in the rarefied air. 



VI. Exhalations continually rife from the furface of phofphorus "when expofcd to the at- 

 mofphere, as is proved by its fpeedy diffipation in that circumftance : but as foon as the air 

 is rarefied to a certain degree, the exhalations cannot rife ; for thcfe particles will not be 

 elevated but during the time that the furrounding air is heavier than themfelves. When- 

 ever, therefore, the air is rarefied to this degree, the exhalations muft remain, and furround 

 the phofphorus from which they came. The union of oxygene with thcfe phofphoric ex- 

 halations muft be then made only in the vicinity of the phofphorus, whence the light from 

 the difengaged caloric muft be feen there only. It is evident that this light will be much 

 ftronger when the phofphoric exhalations do not rife, becaufe the difengagement of the fame 

 quantity of caloric is then made in a more confined fpace than when the phofphoric exhala- 

 tions could rife and be difperfed in the receiver. 



VII. The caloric which is difengaged from the oxygene, and is feen in the rarefied air 

 round the phofphorus in the form of a ftronger light than ordinary, muft, alfo, on ac- 

 count of its greater denfity, give heat to the phofphorus. Hence may be clearly feen the 

 reafon of the combuftion of phofphorus on rarefying the air when it is furrounded with 

 cotton, as before defcribcd. Woollen and cotton ftuffs have the property of preventing the 

 difperfion of caloric *. The caloric which is difengaged round the phofphorus in the rare- 

 fied air is thus retained by the cotton, until its accumulation on the furface of the phof- 

 phorus becomes at length fufficicnt to fet it on fire. When a piece of phofphorus is not 

 enveloped in cotton or fome fimilar fubftance, it does not take fire in the rarefied air, becaufe 

 the caloric which is difengaj^ed near the phofphorus is fo fpecdily difperfed when it is not 

 arrcfted by the cotton, that the phofphorus cannot acquire the degree of inflammation ne- 

 CcflTary to inflame it. 



* Becaufe they impede the circulation of the air, by wliich the heat would clfe be conduced off. N. 



VIII. 



