279. Why do burning coals produce yellow flame?
Because the hydrogen which they contain is combined with some proportion of carbon, which imparts a bright yellow colour to the flames.
280. Why do some of the flames of a fire appear much whiter than others?
Because the quality of coals, and the conditions under which they are burnt, are liable to variation. Some coals yield a heavy hydrogen, called bi-carburetted hydrogen, which burns with a much brighter flame than carburetted hydrogen.
281. Why does bi-carburetted hydrogen burn with a whiter flame than the common coal gas?
Because it is combined with a larger proportion of carbon, to which it owes its increased luminosity.
282. Why do some of the flames of a fire appear blue?
Because the hydrogen which is escaping where those flames occur is pure hydrogen, destitute of carbon.
283. Why does the fire sometimes appear red, and without flame?
Because the volatile gases have been driven off and consumed, and combustion is continued by the carbon of the coals and the oxygen of the air.