Dr. fordyce on the Light , Sec. 505 
affected by the colour of the ignited matter. While zinc 
is calcining, the pure white calx throws off a light, which 
vies with that of the Sun in brightnefs and purity ; the 
green calx of copper gives to the flame of a fire, in which 
it is calcining, a beautiful green; and tallow burning in a 
candle, being converted into empyreumatic oil, as it pafles 
off from the wick, the yellow colour of this oil gives a 
yellownefs to the flame, which very much alters the co- 
lours of objects feen by candle-light from what they 
appear to be in the day. 
The light produced by the decompofition of bodies in 
inflammation is totally independent of the heat, and 
its colour is blue; for fubftances which burn, without 
producing 60 o° of heat of Fahrenheit’s thermometer, 
give light during their inflammation. Thus, pbofpborus 
of urine expofed to the air burns and is decompofed, 
producing light with very little heat; and that this is a 
true inflammation and decompofition appears from this 
experiment. Take a receiver of white glafs, capable of 
holding fix or eight gallons ; put into it a drachm of phof- 
phorus of urine, finely powdered, and half an ounce of 
water; cork the mouth of the receiver, and tye it over 
with a bladder, fo as to exclude the external air; incline 
the receiver to all Tides gently, and afterwards fet it to 
reft ; the powder will adhere to the fides, and the water 
will drain from it. As foon as the water is fufficiently 
drained off, the particles of the pbofpborus will become 
luminous, and emit a thick fmoke : this will continue for 
Tome days; but at laft no more light or vapour will 
1 appear. 
