62 HEAT. 



Under great pressure, increased heat is required to ef- 

 fect fusion. Thus the melting point of sulphur is 

 raised from 226 to 285, by a pressure of 11,880 Ibs. 

 to the square inch. 

 nrj . 138. DISAPPEARANCE OF HEAT IN MELT- 



Wtiat remark- 

 able drcum- TNG . Melting or fusing is effected by heat, 



stance attends 



the melting of and a remarkable circumstance attending 

 it, is the disappearance of the heat which 

 has effected the change. Thus, if a thermometer be 

 applied to ice or snow which has just begun to melt, 

 it will be found to stand at 32. Let the ice be then 

 introduced into a tumbler, and placed on a stove, and 

 the temperature again tested at the moment when the 

 conversion into water is completed. The thermometer 

 will be found again to stand at 32. The water produced 

 is no hotter than the original ice, yet heat has been pour- 

 ing into it, through the bottom of the ves- 

 sel,during the whole process of melting. 

 If a piece of glass of the same size had 

 been subjected to the same heat, it would 

 have grown constantly hotter. It fol- 

 lows that in the case of the ice there 

 has been a disappearance of heat. This 

 disappearance always occurs whenever 

 a solid is converted into a liquid. 



What other ^9. ANALOGOUS DISAPPEARANCE OF 



{ appTarance ACIDITY - Chemistry furnishes other in- 

 does chemistry stances of disappearance, which may help 

 us in understanding this one. If vinegar 

 be poured upon chalk it loses its sourness. It is be- 

 cause a combination has taken place between the acid 



