271. What is coal?

Coal is a "vegetable fossil."272. What is meant by a vegetable fossil?

It is a substance originally vegetable, which, by pressure and other agencies within the earth, has been brought to a condition approaching that of mineral or earthy matter.273. Why do we know that coal is of vegetable origin?

By the chemical components of its substance; and also by the vegetable forms that are found abundantly in coal beds.

Professor Buckland, in his Bridgewater Treatise, speaking of the impressions of plants found in the coal mines, says; "The finest example I have ever witnessed is that of the coal mines of Bohemia. The most elaborate imitations of living foliage upon the painted ceilings of Italian palaces bear no comparison with the beauteous profusion of extinct vegetable forms with which the galleries of these instructive coal mines are overhung. The roof is covered as with a canopy of gorgeous tapestry, enriched with festoons of most graceful foliage, flung in wild irregular profusion over every part of its surface. The effect is heightened by the contrast of the coal-black colour of these vegetables with the light ground-work of the rock to which they are attached. The spectator feels himself transported, as if by enchantment, into the forests of another world; he beholds trees, of forms and characters now unknown upon the surface of the earth, presented to his senses almost in the beauty and vigour of their primeval life; their scaly stems and bending branches, with their delicate apparatus of foliage, are all spread forth before him, little impaired by the lapse of countless ages, and bearing faithful records of extinct systems of vegetation which began and terminated in times of which these relics are the infallible historians."

"Surely every man walketh in a vain show; surely they are disquieted in vain: he heapeth up riches, and knoweth not who shall gather them."—Ps. xxxix.

274. What are the chemical components of coal?

They consist of carbon, hydrogen, oxygen, and nitrogen. The proportions of these elements vary in different kinds of coal. Carbon is the chief component; and the proportions may be stated to be, generally, carbon, 90 per cent.; hydrogen, from 3 to 6 per cent.; the other elements enter into the compound in such small proportions, that, for all ordinary purposes, it is sufficient to say that coal consists of carbon and hydrogen, but chiefly of carbon.275. What is charcoal?

Charcoal consists almost entirely of carbon. It is made from wood by the application of heat, without the admission of air. The hydrogen and oxygen of the wood are expelled, and that which remains is charcoal, or carbon in one of its purest states.276. What is animal charcoal?

Animal charcoal, like vegetable charcoal, consists of carbon in a state approaching purity. It is made from the bones of animals, heated in iron cylinders. It is commonly called ivory black.277. What is the purest form of carbon known?

The purest form of carbon is the diamond, which may be said to be absolutely pure.

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.

"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.

"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?

Because it contains a large amount of water, which must be evaporated before combustion can proceed.286. What is the effect of this evaporation?

A great deal of heat is unprofitably expended in driving off the water of the fuel.287. Why does poking a fire cause it to burn more brightly?

Because it opens avenues through which the air may enter to supply oxygen.288. Why do "blowers" improve the draft of air through a fire?

Because, by obstructing the passage of the current of air over the fire, they cause additional air to pass through it, and therefore a greater amount of oxygen is carried to the coals.289. What is smoke?

Unconsumed particles of coal, rendered volatile by heat, and driven off.290. What is soot?

Carbon in minute particles, driven off with other volatile matters and deposited on the walls of chimneys.291. Why do fresh coals increase the quantity of smoke?

Because they contain volatile matters which are easily driven off; and because, also, they reduce momentarily the heat, so that those matters that first escape cannot be consumed.292. Why do charcoal and coke fires burn clearly and without flame?

Because the hydrogen has been previously driven off from those substances.293. Why is it difficult to light charcoal and coke fires?

Because they contain no hydrogen to produce flame, and assist combustion.

"He hath made his wonderful works to be remembered: the Lord is precious and full of compassion."—Psalm cxl.

A new plan of kindling fires has lately been recommended. Coals are to be laid in the bottom of the fire-place to a considerable depth, then the paper and wood are to be laid on, and then a little coals and cinders over them. This plan of "laying in" the fire is precisely the reverse of that which has been pursued for many years. The theory is, that when the coals in the bottom are ignited, a more even combustion is kept up, whilst the smoke and gas which would otherwise escape, and become as so much waste fuel, is burnt up, and produces heat. We have heard the plan strongly recommended by persons who have tried it, and who testify to the great economy of fuel to which it conduces.