IV. 



CURIOSITIES OF VAPOUR JETS. 

 I. Passing the Hand through a Live-Steam Jet. 



THE fingers of the hand may be passed 

 rapidly, but without rude haste, in succes- 

 sion through a small jet of live steam close to 

 the orifice from which it is issuing. 



This steam is as hot as boiling water, as hot 

 as the scalding steam from a kettle-spout. 

 Why does it not scald ? 



In the first place, it is true steam a vapour 

 so hot as to be approaching the nature of a 

 gas, not a partially condensed vapour, like the 

 visible steam from the kettle, which consists 

 of little droplets of liquid water, that can 

 cling to and collect on the hand, wet it, and so 

 impart to it by conduction the great specific 

 heat which it possesses as water. 



Some steam boilers have a hole cut in the 

 side and fitted with a glass window to permit 

 an observer to view the inside, which is illu- 

 minated for the purpose. Above the water is a 

 clear space, with nothing visible. The steam 

 is true steam, i*ot partially condensed. 



This true steam has, like gases, very little 

 specific heat, even when at a high temperature ; 

 so that the thin film of steam in the jet which 



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