-13.2 ELEMENTARY SCIENCE 



to record large changes of temperature, but it is very sensi- 

 tive to small changes and is frequently used to-day in 

 experimental work. 



The importance of the thermometer in connection with 

 the study of weather is obvious. It is also an invaluable 

 instrument for the physician. The normal temperature 

 of the human body is 98.4 F. Variations from this 

 temperature indicate disease. Especially in the case of 

 fevers, careful records of the temperature of the patient 

 must be kept in order to guide the physician in his treat- 

 ment. In commercial processes such as the refinement of 

 oil or sugar, or the manufacture of steel, temperature read- 

 ings are of the highest importance, since they indicate 

 physical changes which greatly affect the character of the 

 product. Scientific kitchen management also calls for 

 frequent use of the thermometer to show the heat of an 

 oven or for other purposes. 



The Unit of Heat. The unit of heat, measured as to 

 its amount, is the calory. It is that amount of heat 

 necessary at standard pressure to raise the temperature 

 of i cc. (cubic centimeter) of water i C. It is also the 

 amount of heat which i cc. of water gives off when its 

 temperature falls i C., which is what we should expect 

 to be the case, according to the law of conservation of 

 energy. In other words, the amount of heat -which a sub- 

 stance acquires when its temperature rises a certain amount 

 is identical with the amount it gives of when its temperature 

 falls by the same amount. This has been proved many 

 times by actual measurements. 



The number of calories needed to raise the temperature 

 of a substance i C. (or the number which it gives out 



