Page:International Library of Technology, Volume 93.djvu/34

and subtract it from 273 1/3 when below zero. Thus, 60° C. = 273 1/3 + 60 = 333 1/3° C, absolute; 10° C. = 273 1/3 − 10 = 263 1/3° C, absolute.

To find the centigrade temperature of a body from its absolute temperature, subtract 273 1/3 from the absolute temperature. Thus, 300° absolute = 300 − 273 1/3 = 26 1/3° C. If the absolute temperature is less than 273 1/3, subtract the absolute temperature from 273 1/3, and the result will be the centigrade temperature below zero. Thus, 250° absolute = 273 1/3 − 250 = 23 1/3° C. below zero.

14. Changing From Centigrade to Fahrenheit. — It is frequently necessary to change from one scale to the other. For example, what would 80° C. be on the Fahrenheit scale? Since the number of degrees between the freezing point and the boiling point on the centigrade scale is 100, and on the Fahrenheit 180, 1° C. will equal 100/180° C. = 5/9° F. Likewise, 1° C. will equal 180/100° F. = 9/5° F.

Rule. — To find the Fahrenheit temperature , multiply the centigrade temperature by 9/5 and add 32. If the given temperature is below zero, and when multiplied by 9/5 gives a greater product than 32, subtract 32; the result is the Fahrenheit temperature below zero.

Example. — What will be the reading of a Fahrenheit thermometer if a centigrade thermometer indicates a temperature: (a) of 100° C? (b) of -30° a?

Solution. — Applying the rule, (a) 100 × 9/5 - 180; 180 + 32 = 212° F. Ans. (b) 30 × 9/5 = 54. Since the given temperature is below zero and its product by is greater than 32, − 30° C. − 30 × 9/5 − 32 = 22° F. below zero. Ans.

15. Changing From Fahrenheit to Centigrade. To change Fahrenheit temperatures to their centigrade values, the following rule may be used:

Rule. — (a) If the given Fahrenheit temperature is 32° or greater, subtract 32 from it. (b) If the given Fahrenheit temperature is between 0° and 32°, subtract it from 32. (c) If the given Fahrenheit temperature is below 0°, add 32 to it.