267. Why does a candle burn dimly when the wick has become loaded with carbon?
Because the carbon radiates the heat, and disperses it, and reduces the heat of the flame below that temperature which is essential to its luminosity.
268. What differences characterise the combustion of carbon and of hydrogen?
The combustion of carbon takes place without the production of flame. The charcoal (or carbon in any other form) being heated to redness, enters directly into combination with the oxygen of the surrounding air, and the carbonic acid gas, being invisible, passes away unobserved.
But in the combustion of hydrogen the heat developed is so intense as to render the gas itself luminous, just as iron may be heated to a red or white heat.
269. What has become of the candle when it has been burnt?
It has been resolved partly into carbonic acid gas which, though unperceived, has diffused itself through the surrounding air; and partly into water, which escaped in the form of thin vapour.
270. Has any part of the candle been consumed or lost?
No; there is no such thing as "loss" in the operations of nature. Every particle of the candle, now invisible, exists either in the form of gas, vapour, or water, with, perhaps, a few solid particles that may be called ashes, but which are too minute to excite attention.