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. = $273 1⁄3$ &minus; 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 &minus; $273 1⁄3$ = $26 1⁄3$° 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 = $273 1⁄3$ &minus; 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. —

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

— Applying the rule, (a) 100 &times; $9⁄5$ - 180; 180 + 32 = 212° F. Ans. (b) 30 &times; $9⁄5$ = 54. Since the given temperature is below zero and its product by is greater than 32, &minus; 30° C. &minus; 30 &times; $9⁄5$ &minus; 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. —