HEATING BY STEAM. 829 



This consists of thick parallel threads which are interwoven with 

 fhinner threads. A very short piece of a thick thread should be 

 pulled off the end of a piece and used for the experiment. 



The production of sensible heat during the solidifi- 

 cation of liquids as, for example, in the former experi- 

 ment with hyposulphite of soda of which the point of 

 solidification had been retarded has not yet found any 

 practical applications. The heat produced during con- 

 densation of steam may however be advantageously 

 used for heating substances which cannot be exposed 

 to an open flame. In a vessel of wood or of thick glass 

 which cannot be directly heated over a flame, because 

 the one would burn and the' other crack, cold water 

 may be made to boil by passing a jet of steam into the 

 water through a tube. The great advantage of this mode 

 of heating by steam is that the temperature produced 

 cannot exceed definite limits; for example, in heating 

 the water hammer, fig. 396, by steam since it is impos- 

 sible that the apparatus can be heated beyond 100, 

 the pressure in the interior can never exceed that of 

 the atmosphere, and therefore we need not fear that 

 the apparatus will be broken. 



When a solid body is liquefied, a certain quantity of 

 heat must be supplied to it ; this heat disappears, or 

 becomes latent, and the temperature of the body 

 remains the same. But if a body is liquefied without 

 receiving a supply of lieat from without, then, since heat 

 is under any circumstances necessary for producing the 

 liquefaction, a diminution of temperature must take 

 place. It has been previously stated (see page 213) 

 that a number of solid bodies dissolve in certain 

 definite liquids because the adhesion between the solid 



