286 



SCIENTIFIC AMUSEMENTS. 



heat disappears entirely ; the 80 units of heat contained in the 

 original hot water are said in this case to become latent, whilst 1 

 Ib. of ice is melted ; or otherwise, the quantity of heat rendered 

 latent during the fusion of ice (latent heat of fusion) is said to 

 be 80 units. 



The reason why snow and salt and other mixtures of saline 

 matters with ice or snow (Expts. 21, et seq.) become chilled, is 

 simply that by virtue of their chemical or physical action on one 

 another the ice becomes melted and dissolves the solid, 'forming an 

 aqueous solution ; heat is necessarily rendered latent during the 

 fusion of the ice, and consequently the temperature of the liquid 

 falls greatly. 



Fig. 134. Latent Heat of Steam. 



Expt. 331. Latent Heat of Vaporisation. Into the mouth of 

 a flask (a) fix airtight a perforated cork with a piece of quill 

 glass tubing (b) bent as shown in fig. 134, so that if water be boiled 

 in the flask the issuing steam can be blown into a cylinder (c) 

 containing water, whilst any water mechanically spirted upwards 

 will run back into the flask by the sloping tube (b). Measure into 

 the cylinder any convenient quantity (say J pint = 10 ounces) of 

 water chilled down to by pieces of ice, but not containing any 

 solid lumps of ice. Now blow a current of steam into the ice cold 

 water by boiling water vigorously in the flask, and keep the ice 

 water constantly stirred with a thermometer; you will observe 

 that the temperature continually rises until the thermometer 



