2. Which _three_ of the _effects_ of heat do _you_ make most use of? Explain what use you make of each of these effects. 3. Which of the forms of energy can be transformed into heat? How in each case? 4. Into what other forms of energy may heat be transformed? Name the device or process used in each case. 5. What five different commodities are purchased by people in your neighborhood for the production of heat? Which of these costs least for the amount of heat furnished? Which is most expensive? How do you determine these answers? 6. Why do many people buy heat in an expensive form, as in using an electric toaster, when they can obtain it in a cheaper form by burning gas or coal? 7. How many of the five effects of heat have you observed outside of school? (2) TEMPERATURE AND EXPANSION =141. Heat and Temperature.=--We should now clearly distinguish between the terms, _heat_ and _temperature_. Heat is _a form of energy consisting of molecular motion_. The temperature of a body is its _degree of hotness_. The _amount of heat_ present in a body and its _temperature_ are very different things. The temperature refers to the intensity of the heat in the body. A quart of water and a red hot iron ball may contain _equal amounts_ of heat, although the ball has a _much higher temperature_ than the water. A cup of boiling water will have the same temperature as a tank full of boiling water, but the tank will contain more heat. Every one knows that it will take longer to boil a kettle full of water than a cupful. A hot-water bag, holding 2 quarts of water will give off heat longer than a 1-quart bag, both being filled with water at the same temperature. To put it in another way, more work is done in heating a large amount of water, than a small amount through the same change of temperature. =142. Units of Heat and Temperature.=--There are two common units for measuring heat: the _Calorie_ and the _British thermal unit_. The _calorie is the amount of heat required to raise the temperature of a gram of water one centigrade degree_. The British thermal unit is _the amount of heat required to raise the temperature of one pound of water one Fahrenheit degree_. One of the units plainly belongs to the metric system, the other to the English. An instrument for measuring temperature is called a _thermometer_. Various scales are placed upon thermometers. The two thermometer scales most commonly used in this country are the _Centigrade_ and the _Fahrenheit_. The _Fahrenheit thermometer scale_ has the temperature of melting ice marked 32°. The boiling point or steam temperature of pure water under standard conditions of atmospheric pressure is marked 212° and the space between these two fixed points is divided into 180 parts. The centigrade thermometer scale has the same fixed points marked 0 and 100 and the space between divided into 100 parts. (See Fig. 123.) The centigrade scale is the one used by scientists everywhere.