Hence we derive another of the beautiful lessons of science--a lesson which teaches us to _despise nothing that God has given_. The soot which blackens the face of a chimney-sweep, and the diamond that glistens in the crown of the monarch, consist of the same element in merely a different atomic condition. What a lesson of humility this teaches to Pride! The haughty beauty as she walks the ball-room, inwardly proud of the radiance of her gems as they rise and fall upon her breast, little thinks or knows that _every breath that is expired around her wafts away the like element of which her treasures are composed_. That even in our own flesh and bones the same abounding substance lies hid; and that the buried tree of the primitive world, and the little flower of to-day, are both the instruments of giving this singular element to man! 278. _What is coke?_ Coke is coal, divested of its hydrogen and other volatile parts, by a similar process to that by which charcoal is produced. It forms the residue after hydrogen gas has been made from coals. It consists almost entirely of _carbon_. [Verse: "Oh that men would praise the Lord for his goodness, and for his wonderful works to the children of men."--PSALM CVII.] 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. 284. _What effect has the burning of a fire upon the composition of the air?_ It is found that in burning 10lb. of coal the oxygen contained in 1,551 cubic feet of air is altogether absorbed. It is therefore necessary to keep the atmosphere of a room, in which a coal fire is burning, fresh and pure, to supply 155 cubic feet of fresh air for every pound of coal that is consumed. [Verse: "O Lord how manifold are thy works, in wisdom hast thou made them all: the earth is full of thy riches."--PSALM CIV.] 285. _Why does wood which is "green" hiss and steam when it is burnt?_