dough in bread making. As a result of the action of yeast, the sugar in bread is broken down into carbon dioxide and small quantities of alcohol. The firm dough then swells because the gas imprisoned within it forms air spaces. In baking the dough, the spaces are enlarged as the gas escapes, and at the same time the alcohol is evaporated. Yeast is not always used to produce this carbon dioxide. Sometimes, as in soda biscuits, baking soda (bicarbonate of soda) is used and to it is added cream of tartar or sour milk. In either case, by the action of the cream of tartar or the sour milk upon the soda, carbon dioxide is given off. If baking powder is used, as in baking powder biscuits, cakes, and many other foods, the action of the substances within the baking powder is such as to liberate carbon dioxide. This escapes through the dough and makes it light and porous. Questions Chemically speaking, what is charcoal? 2. How is charcoal made? 3. To what various uses is it put? 4. How is lampblack produced? 5. Has lampblack a commercial value? What is it? 6. What is coal? 7. What are the successive stages in its formation? 8. Look up all the material you can on coal forma tion and write an essay on it. 9. How is coke made from coal? 10. For what purposes is coke used? 13. How are lead pencils made? 14. Diamond and coal are both carbon. What causes the great difference in the market values of these two substances? Three reasons. 15. Where are the best diamond mines located? 16. Do you know how diamonds are mined? Look it up and bring this information to class with you. 17. How is carbon dioxide produced? 18. Is it necessary to life? 19. Is it poisonous ? 20. Would too much of it prove fatal to life? Why? 21. Explain fully why people and other animals are sometimes killed in going down into old wells and mines. 22. What is the test for the presence of carbon dioxide? 23. Is there any soda in "soda water"? 24. Whence then does it receive its name? 25. What causes the effervescence of "soda water"? CHAPTER X PHOSPHORUS (Phosphorus =P) Introduction. Phosphorus is not found in the free state in nature, but in compounds, in small quantities rather widely distributed. It is a part of all living matter and is found in all fertile soils, as plants can not grow without phosphorus. Large deposits of minerals are found containing phosphates, which are extensively mined for use as fertilizers. Bone consists of 80% of calcium phosphate, which, together with the phosphates found in large mineral deposits, form the chief sources of commercial phosphorus. Preparation. In obtaining phosphorus from bones the combustible matter is burned out, leaving bone-ash behind. Bone-ash or a pure mineral phosphate is then heated with sand and carbon in an electric furnace. In the heating, phosphorus vapor escapes through tubes and is led under water where it condenses in molds. Properties. Yellow phosphorus in the pure state is a translucent, waxy solid which when exposed to light takes on a coating of darker color. If a piece of yellow phosphorus is exposed to the air, it will begin to give off white fumes almost immediately and if left thus exposed for a minute or two, will ignite. Because it ignites at such a low temperature, phosphorus must Fig. 31. Phosphorus furnace. A mixture of calcium phosphate, sand, and carbon is admitted at H through T. T is then closed and T' opened. The mixture is slowly admitted over the screw S and drops between electrodes A and C. The slag which forms flows out at M. Phosphorus vapor and carbon dioxide pass out through R. The phosphorus condenses in the water W, and the carbon dioxide bubbles up and passes off through the water. always be kept under water. It must always be cut under water, for the friction of the knife caused in the cutting will raise its temperature to the point of burning. Great care must be exercised in dealing with phosphorus and forceps should be used to handle it. If touched by the hands the heat of the body may ignite it and cause a burn. A phosphorus burn is very serious, the wound requiring months to heal. Phosphorus is very poisonous, and great care must be taken not to breathe the fumes. Because of the rapidity with which oxygen and phosphorus unite, phosphorus emits a light when exposed to air. This property is known as phosphorescence. If yellow phosphorus is heated in closed vessels to a temperature of 250°C. to 300°C., its nature changes completely, producing the form called red phosphorus. On further heating it undergoes another change and becomes yellow phosphorus once more. Red phosphorus is a dull red, powdery substance, very inactive and perfectly safe to handle. It does not give off a light as does the yellow phosphorus, neither is it poisonous. Uses of phosphorus. Because of its poisonous nature yellow phosphorus is used in preparing poison for rats, mice, and other vermin. Its chief use, however, as well as that of the red phosphorus, is in the .anufacture of matches. Friction match. In preparing the common friction match, the end of the stick is soaked in a mixture usually containing paraffin, sulphur, phosphorus, glue, and some compound containing a great deal of oxygen. On striking the match the heat produced from the friction kindles the phosphorus, which unites with the oxygen in the compound on the head of the match, and also with the oxygen in the air. The sulphur and paraffin are then ignited, and their burning sets fire to the wood. Safety match. The safety match differs from the |