ON METHODS OF DETERMINING THE DRYNESS OF STEAM. 411 



approximate, and the difference is less than that which may be due to 

 unavoidable inaccuracy in reading the i-)ressure gauge. Since in ordinary 

 use about 20° fall of the temperature ^_>' corresponds to 1 per cent, of 

 moisture in the steam, it appears that the calculated value of t^ for dry 

 steam is practically exact. Other experiments (though not over any great 

 range of pressures) have been made. So far as they have gone, they con- 

 firm this result. Hence it appears that no correction of the theoretical 

 calculation is necessary to obtain practical accuracy, and that the assump- 

 tion that all the kinetic energy at the orifice reappears as heat is prac- 

 tically true. 



In fig. 6 the temperature curves for the experiment above have been 

 plotted. The saturation temperature ^j, due to the steam pressure, calcu- 

 lated from the pressure-gauge readings, and the actual temperature of 

 the superheated steam <,, are shown by the two upper lines. The tem- 

 pei-ature of the superheated steam in the second chamber t^^ is shown 

 by a full line, and the calculated v^alue of t^<, by a dotted line. The 

 thermometer being in an iron tube necessarily lags a little behind the 

 temperature in the chamber. 



Test of a comhined Separating and Wire-draioing Calorimeter hy Mr. 

 Barrus. — A very careful test is given by Mr. Barrus in his paper,' in 

 which the steam passing through the instrument was condensed in a 

 surface condenser and measured. Pairs of trials were made under identical 

 conditions ; in one the separator was in use, and in the other the separator 

 was shut off. Each trial lasted usually an hour, sometimes two hours. 



Pairs of Trials in one of tchich most of the Moisture was trapped in the 

 Separator, and in the other the whole measured by Wire-drawing or 

 Heat Gauge. 



Mr. Barrus has used these results in an attempt to calculate a value 

 for the specific heat of superheated steam, and gets values ranging from 



' Amer. Soc. Mechan. Engineers, 1890. 



