Elements of the theory and practice of cookery

33. The story of coal. — Coal, by composition and structure, is shown to be of plant origin. Leaves, ferns, bark, whole tree trunks even, have been found turned to coal in mines. The slow process of decay that effected this change took place long before men lived on the earth, at a time when the land was covered with thick forests different from any growing now. Many trees then resembled gigantic ferns. Evidently these forests were flooded from time to time, the trees being over- thrown and buried beneath sand washed in by the water. The flood subsiding, a new forest arose, to be in turn similarly buried. Pressure, combined with heat greater than now prevails anywhere on earth, slowly carbonized PREPARATORY LESSONS 21 these layers of plant-substance into seams of coal. This period is known as the Carboniferous Age. 34. Coal works for us. — The heat of burning coal may be utilized to cook food, melt iron, make steam to drive engines, and do hundreds of other kinds of work. A person able to work is said to have energy. Whence comes the energy of coal ? From its carbon ; and to find out where that came from we must go back to the Carboniferous Age. 35. The heat of fires conies from the sun. — The carbon taken in by plants becomes, we know, part of the plants ; but only with the aid of sunlight can they breathe in carbon dioxide from Avhich to obtain carbon. (§ 6.) The sun, then, is the source of the energy in coal ; we may say that the sun lights our fires, Stephen- son, the inventor of the locomotive, when asked what drove his engine, answered, " Bottled-up sunshine." He spoke the exact truth ; the sun's energy is stored up in coal-mines until, with pick and blasting powder, man sets it free. 36. Hard and soft coal ; buying coal. — Hard, or anthracite, coal is the result of almost perfect carboni- zation of wood ; in soft, or bituminous, coal the process has not gone so far.^ The latter is crumbly and dull, and burns with much smoke. Which yields the more heat, i.e. has the more energy, hard or soft coal ? Hard 1 Wood contains about 50 per cent of carbon, bituminous coal about 77 per cent, antliracite about 90 per cent. All coal contains sulphur. 22 THEORY AND PRACTICE OF COOKERY coal is best for household use. A good quality is jet black and glossy, breaks into roughly cube-shaped pieces, is free from slate, and yields little clinker. For a stove with a small fire-box, use "chestnut" coal; for most ranges a mixture of " stove " and " chestnut " is desir- able. Too small coal will fall between the bars of the grate before being burned. It is prudent to buy a year's supply of coal in summer, when it is cheapest ; coal bought by the pound or basket costs about three times as much as if bought by the ton. 37. How to save coal and gain heat. — Coal burns at first with a blue flame, but when thoroughly afire, with a clear, red glow. When white-hot, almost all its -heat- giving power has been exhausted. A good coal fire consists of a mass of red coals covered by a layer of black ones heating and ready to kindle when the red ones die out. More heat is gotten from the same quan- tity of coal by adding it to the fire a little at a time than by putting it on all at once.