VOL. LXVr.l PHILOSOPHICAL TRANSACTIONS. Q5 



flammation and decomposition appears from this experiment: take a receiver of 

 white glass, capable of holding 6 or 8 gallons ; put into it a drachm of phos- 

 phorus of urine, finely powdered, and half an ounce of water ; cork the mouth 

 of the receiver, and tye it over with a bladder, so as to exclude the external air ; 

 incline the receiver to all sides gently, and afterwards set it to rest ; the powder 

 will adhere to the sides, and the water will drain from it. As soon as the water 

 is sufficiently drained off, the particles of the phosphorus will become luminous, 

 and emit a thick smoke : this will continue for some days ; but at last no more 

 light or vapour will appear. Open the receiver, and you will find that the air 

 will have contracted, as it does from the inflammation of a candle in Van Hel- 

 mont's experiment ; that is, about a "lOth part. It is become unfit for inflam- 

 mation ; for if a lighted candle be immersed in it, it will be extinguished as well 

 as the phosphorus, and an animal will be suffocated by it. The air then has 

 sufi^ered the same change, as that air which has served for the inflammation of 

 other bodies; and the phosphorus is partly decomposed, the water in the re- 

 ceiver being impregnated with its acid, and the air saturated with its phlogiston. 

 Blow fresh air into the receiver, and the light and smoke will immediately 

 re-appear. In like manner, it is known that sulphur will burn and give light 

 without heat sufficient for ignition. Take a piece of iron heated nearly red hot, 

 and throw a little gunpowder on it. If the heat be of a proper degree, the sul- 

 phur will burn off" with a blue flame, without heat sufficient for ignition ; for 

 if such heat had been produced, the gunpowder would certainly have taken fire, 

 which it does not. It is the inflammation and decomposition of the sulphur, 

 and not its evaporation, which produces light ; for if we sublime sulphur in close 

 vessels, made of the most transparent glass, no light will be visible, except at 

 the very beginning, when a small portion of it burns till the air in the vessel be 

 saturated, and rendered unfit for inflammation. 



That the light produced by the decomposition in inflammation is blue, in 

 whatever degree of heat the inflammation takes place, appears from observing 

 the bottom and lower part of the flame of a candle, where the inflammation is ; 

 the light produced is blue. Or take a candle which has burnt for some time, 

 extinguish it by applying tallow to the wick, and let it stand to cool ; afterwards 

 set it on fire by the flame of another candle : at first no more vapour will arise 

 than can be acted on by the air at once ; inflammation therefore will go on in the 

 whole small flame, and it will be blue. It may be necessary to observe here, 

 that when a candle burns, the following process happens : the tallow boils in the 

 wick, and is converted into empyreumatic oil, rising from it in the form of 

 vapour. As it rises from every part of the wick, the volume is increased till it 

 comes to the top, and gives to the lower part of the flame the form of a frus- 

 trum of an inverted cone. The air is applied to the outer surface of the column 



