THE THERMOMETER
Besides the ordinary thermometer the school should possess a chemical thermometer graduated from 0° Fahrenheit to 212°.
1. Our sensations vary so much under different circumstances and in different individuals that they cannot be depended on. Find examples of this and show the need of a measuring instrument.
2. The pupils can learn, by examination of the common wall instrument, the parts of the thermometer—tube, bulb, liquid (alcohol or mercury), and scale.
3. Repeat the experiment for expansion of liquids, showing wherein the apparatus resembles the thermometer, warm the thermometer bulb and watch the column rise; cool it and note the fall.
4. Set the bulb of the chemical thermometer in boiling water. The mercury comes to rest near 212°. Bury the bulb in melting snow and notice that the column falls to 32°. Give names for these points. Explain that a degree is one of the 180 equal parts which lie between boiling point and freezing-point. Show that 32° below freezing must be 0°, or zero.
5. The uses of thermometers for indoors and outdoors; for dairy, sick room, incubator, and soils; maximum and minimum. Dairy thermometers registering 212° Fahrenheit may be obtained; they are cheaper than chemical thermometers.
EXPANSION OF AIR
Half fill a flask with water and invert it uncorked over water in a plate. Apply a cloth soaked in boiling water to the part that contains air. Why does the water leave the flask? Apply cold water. Why does the water return? Any ordinary bottle may be used in place of the flask, but it is more liable to crack.
Make an air thermometer. See The Ontario High School Physics, page 223, also Science of Common Life, page 41. Try to graduate it from the mercurial thermometer. Have the boys make a stand for it.