338 LATENT AND SPECIFIC HEAT. 



(2.) How many pounds of steam at 100 C. will just melt 100 

 pounds of ice at C. ? If a; represent the number of pounds of 

 steam required, that quantity of steam at 100 C. will furnish 637# 

 heat units. To melt 100 Ibs. of ice, (80 x 100 =) 8,000 heat units 

 will be required. 



Hence, 637z = 8,000. ! '*. x = 12.55 + Ibs. Am. 



(3.) What weight of steam at 100 C. would be required to raise 

 500 pounds of water from C. to 10 C. ? 



Let x = the number of pounds of steam required. 



(537 + 90)z = 500 x 10. .-. x = 7.97 + Ibs. Ans. 



(4.) If 4 Ibs. of steam at 100 C. be mixed with 200 Ibs. of water at 

 10 C., what will be the temperature of the water ? 



Let x = the temperature. In condensing to water at 100 C., the 

 4 Ibs. of steam will give out (537 x 4 =) 2,148 heat units. This 

 4 Ibs. of water will then give out 4(100 x) heat units. Hence, the 

 steam will impart 2,148 + 4(100 x) heat units. The 200 Ibs. of 

 water in rising from 10 C. to x will absorb 200(z 10) heat units. 



Hence, 2,148 + 4(100 - x) = 200(z - 10). .'. " x = 22.29 C. Ans. 



531. Illustration of Specific Heat. When 

 the temperature of a body changes from 30 to 20, the 

 body loses just as much heat as it gained in passing from 

 20 to 30. This heat lost by a cooling body may be 

 measured, like any other energy, by the work it can per- 

 form. If equal weights of different bodies be raised to the 

 same temperature, the amount of ice that each can melt 

 will be proportional to the number of thermal units they 

 severally contain. A pound of sulphur at 212 F. will 

 melt as much ice as a pound of boiling water. Hence, 

 it required only | as much heat to heat the sulphur from 

 the freezing point to 212 F., as it did to heat the water 

 to the same temperature; in scientific phraseology, the 

 specific heat of sulphur is . 



(a.) In an experiment of this kind, if the cooling substance change 

 Its condition, the latent heat set free as sensible heat must be taken 

 Into account. Special precaution must also be taken in measuring 



