Food and health

'' It seems to me," said Marjorie, " that there must be some way to measure just the amount for Grandmother, for you and Father, and for all of us children.'' " Why don't you ask Miss James ? " said her mother. ** I am so glad you wanted to ask that question," remarked Miss James, when Marjorie brought this thought to the class. How is temperature measured by a thermometer? '' How would you explain the use of the thermometer to some one who did not understand ? " was Miss James' first question. We learned long ago that the amount of heat in things around us changes from time to time, sometimes very quickly. Take water, for instance : how rapidly it heats and begins to boil over a good fire, and how soon it freezes when the weather is cold. The words in common use for the different degrees of heat are cold. cool, hot, warm, tepid, lukewarm, and so on. These words are not exact, however ; and people found it necessary to measure heat in some definite way. Mercury and alcohol are substances that change very rapidly with only a slight increase or decrease in temperature. They change in bulk and expand or shrink. Look at a thermometer, and see that the mercury is inclosed in a bulb and a tube, fastened upon a scale. Who made the scale ? Several people, and so we have thermometers (heat measures) of more than one kind. The Centigrade is the best because it is the simplest. The freezing point of water is called zero; and the boiling point of water, lOO ; and there are one hundred steps (Centigrade) between, which we call degrees. Scientists prefer to use Centigrade. We should become familiar with the Centigrade thermometer in daily life. In America, however, we are slow to change in matters of measure and weight. The French, who planned the decimal system of weights and measures, and who use them in buying and selling, are much more sensible than we. In America and England, the Fahrenheit is used. This scale was made and used by Gabriel Daniel Fahrenheit. The freezing point is at 32*^ above the zero of this scale, and the boiling point at 212*^ above ; and there are 180 degrees (Fahrenheit) between. So you see, one degree Fahrenheit is equal to 5/9 degrees Centigrade.. Here is the picture (Fig. 119) of a thermometer with •both Fahrenheit and Centigrade scales. You should learn to use the latter just as soon as possible. Do you not consider decimals easier and more convenient than common fractions ? The degree on the scale of a thermometer is one kind of heat measure. We have another measure for the needs of our bodies and the energy contained in our foods ; for we calculate the amount of food .Melting point of cxxmnon solder 3S0 2S0 ^Boiling point of water at normal pressure 1^ Pasteurizing milk ? Normal temperature of human body (98.5) Rooms V7here occupants are not exercising • Tree Xing point of water ^ 39 IVeezing point of mercury Fig. 119. ^ Two common temperature scales, viz. Fahrenheit and Centigrade. On the Centigrade scale the freezing point and normal boiling point of water are, respectively, o** and 100°; on the Fahrenheit scale these points are 32® and 212®; thus i® Centigrade is equal to 1.8** Fahrenheit. we need by the amount of energy it will furnish the body. What is a calorimeter ? Scientists have learned to measure heat given off by shutting up some person, or Courtesy of Professor Qraham Lmk. Fig. 120. — Respiration calorimeter, open. From the "Journal of Biological Chemistry."^ lower animal, in a machine where he has air and is quite comfortable for a time. Here is a picture (Fig. 120) of one machine called a calorimeter (heat measure) for a small animal. You can see how elaborate and delicate a machine it is, and it does exactly record the