336 



LATENT AND SPECIFIC HEAT. 



FIG. 255. 



(&.) The change of latent heat into sensible during the condensa 

 tion of a gas is easily illustrated 

 by the following experiment : 

 Into a gas bottle, A, put a tea- 

 cup full of small pieces of mar- 

 ble, and pour in enough water to 

 cover them and to seal the lower 

 end of the thistle tube. From 

 the gas bottle lead a delivery 

 tube to the lower part of a bot- 

 tle, B, containing a thermome- 

 ter, t. From this bottle lead a 

 tube to the lower part of the 

 bottle C, which contains a ther- 

 mometer, T, with its lower part embedded in a teacup full of salts 

 of tartar. Through the thistle tube of A pour muriatic acid, about a 

 thimble-full at a time. Carbonic acid gas will be liberated and pass 

 through B into (7. There it unites with the potassium carbonate, 

 changing it to potassium bi-carbonate. In this change from the 

 aeriform to the solid condition, the carbonic acid gives up all its 

 latent heat, as is shown by the remarkable rise of the thermometer 

 in C. That this increase of temperature is not due to the sensible 

 heat of a hot gas is shown by the fact that t is scarcely affected 

 during the experiment. 



(c.) When the vapor is condensed to the liquid or solid form, the 

 heat previously rendered latent is given out as sensible heat ; that 

 is, the energy of position is changed back to energy of motion. In 

 coming together again, the particles yield the same amount of 

 kinetic energy as was consumed in their separation. 



528. The Latent Heat of Water. If 1 Ib. of 



water at C. be mixed with 1 Ib. of water at 80 C., we 

 shall have two pounds of water at 40 C. But if 1 Ib. of 

 ice at C. be mixed with 1 Ib. of water at 80 C., we shall 

 have two pounds of water at C. The heat which might 

 be used to warm the water from to 80 C., has been used 

 in melting a like weight of ice. Hence, by our definition, 

 we see that the latent heat of water is 80 C. (or 144 F.) 

 This means that the amount of heat required to melt 

 a quantify of ice without changing its tempera- 



