DAVIS. — CERTAIN THERMAL PROPERTIES OF STEAM. 



271 



sudden rise in Thomas' curves near saturation indicates, according to 

 his interpretation, that a comparatively large amount of heat is re- 

 quired to change dry steam into slightly superheated steam. But it 

 may also indicate that what he believed to be dry steam really carried 

 a small amount of water floating as a mist. This would have to be 

 evaporated at the expense of some extra heat in addition to that re- 

 quired for the actual superheating, and C p would come out too large. 



.100 



.200° .250° 



Figure 2. 



That this explanation is a reasonable one is shown by a comparison of 

 his apparatus with Knoblauch's. The latter's preheater, mentioned 

 above, was a pipe made up of 15 sections each 20 cms. in diameter and 

 20 cms. long, each filled with a dense grid of constantan ribbons which 

 ensured thorough mixing of the passing steam. All of the heat neces- 

 sary for the desired superheating was ordinarily put in in the first one or 

 two sections, and the sole purpose of the rest of the preheater was to 

 bring the resulting mixture of highly superheated steam and floating 



