Elements of the theory and practice of cookery

38. By the first method the coal gets sufficient air to be burned to carbon dioxide (CO;,) ; by the second, much of it is burned to carbon monoxide (CO), thus taking up only half as much oxygen as it is capable of uniting with, and of course, producing less heat. 39. Kerosene, or " coal-oil," prepared from the mineral oil petroleum, is the cheapest household fuel, and is safe when of good quality and when burned in stoves intended for it. Never use kerosene to kindle a ivood or coal fire. When heated, it gives off vapor that in con- tact with fire is likely to explode. PREPARATORY LESSONS 23 I 40. Natural gas, used for heating and ligliting, flows I from the ground. Both it and coal-oil are believed to be of vegetable origin. What is the source of their energy ? Artificial gas is made from coal. In The Fairyland of Science, you will find an interesting chapter, illustrated, on " The History of a Piece of Coal." Coal and the Coal-mines tells all about coal, and has pictures of Pennsylvania I mines, plant forms found in coal, etc. I Another good book (not quite so simple as this) is Chemistry in Daily Life. For information about primitive ways of obtaining i fire, and about Matches and Phosphorus, see pp. 17-22; Petroleum, ' pp. 28, 29; Gas and Gas-stoves, pp. 83-36. Chapter VII of Home Economics tells some things not mentioned I in this text-book, about fuels and fires. Domestic Science in Gram- mar Grades tells about "The Evolution of Fire," on p. 29, and about " Ancient Forests and Modern Fuel," on p. 32. Section 3. "Water Men really know not what good water's worth. — Byron. 41. Water in nature. — Water occurs more commonly and in larger quantities than any other liquid.* It exists not only in the ocean and in other bodies of water, but in plants, the bodies of men and animals, and even in rocks and other things that seem quite dry. Air contains water ; some fruits consist of little but water and flavoring, with just enough solid matter to give them form ; our own bodies are about three-fifths water. Water is called "the universal carrier." It carries soil from place to place, piling in valleys what it washes away from hills ; it bears seeds from one shore to plant 24 THEORY AND PRACTICE OF COOKERY them on another. It is the water in sap that enables it to flow through plants, carrying material to build them up ; it is the water in blood that enables it to do the same for the animal body. Without water there is no life ; a seed kept dry never sprouts ; an unwatered plant dies. Water as a Solvent 42. Much of the material carried by water is dis- solved in it. Experiments in solubility. — A. Put a level teaspoonful of salt into a glass of cold water. AVhen the salt has disappeared taste the water. Put another teaspoonful into hot water. In which does the salt disappear more quickly ? Try the same experiment with powdered chalk. Salt is soluble in water ; chalk is insoluble in water. Hot water dissolves salt more quickly than cold water does ; that is, it is a better solvent for it. B. .Find out which dissolves faster, a whole lump of sugar, or a lump broken into bits ; coarse or fine salt. Water dissolves more substances than any other liquid. To this property it owes much of its carrying power. The more finely divided a substance is the more rapidly it dissolves. Why ?