

THE THERMODYNAMICAL PROPERTIES OF sri'KKIII . \ I I I . <l\-.\\\. -_>| 



examination of the pressures and quantities of steam through the orifice j>er minute, 

 it appears that the reading at the pressure 14 '95 Ibe. in Experiment 28 will most 

 prol>ably feel the effects of this energy of motion to the greatest extent. 



Taking now the sectional area of the channel, using the maximum rate of discharge 

 <.f the strain in this exj>eriment (1 Ib. in 4'8 minutes), and making an approximation 

 t<. the density of steam at a pressure 14 -95 Ibs. per square inch and temperature 

 :HP6 F., the velocity of the steam at the place where the thermo-junction is 

 placed works out at 41 '6 feet per second. The energy of motion per Ib. of 

 strain at that velocity is 54*1 work units or 0'07 B.T.U. Taking the specific 

 heat of superheated steam as 0'5, the fall of temperature due to this energy of 

 motion is 0'14 F., which is much less than the experimental error, and, as this 

 \\ill be probably the maximum fall, being very much less than this for by far the 

 greater part of the readings taken, it will not be necessary to make any corrections 

 upon this head. 



The effect of the velocity of the steam on the observed pressure may also be 

 approximately calculated ; but, taking the maximum quantities, the loss of pressure 

 due to this cause never exceeded O'l Ib. on the sq. inch, and, as it is usually very 

 much less than this, we need not take this loss into account. 



SECTION XIII. On the Position of the Thermo-junction in the Steam. 



After Experiment 27 had been made, a second thermo-junction was inserted in the 

 channel on the low pressure side of the orifice, the junction being placed in the hori- 

 zontal portion of the channel, about 3^ inches from the orifice. The wires from this 

 junction passed out of the channel between the two flanges at the end pp, fig. 3, of 

 that portion covered by the steam jacket. Another similar junction in the same 

 circuit was placed in the oil bath, and the galvanometer was brought into the circuit 

 by the same process as with the previous circuit, viz., by dipping the ends of the wires 

 into mercury cups into which the ends of the wires from the galvanometer can be 

 <lil>j>ed. By this means either the old circuit or the new one can be brought into the 

 galvanometer circuit. As the above alteration includes the making of an entirely new 

 circuit, which is differently placed in the apparatus to the old one, small differences 

 may exist between the readings given by the two circuits. Hence in any experiment 

 made with the aid of the new circuit the thermometric observations should be 

 corrected by again comparing the temperatures found with those of saturated steam 

 under known pressures, using this same circuit to effect the comparison. An experi- 

 ment was then made with the new circuit in position, with the object of ascertaining 

 whether the superheated steam had different temperatures in different jMirts of the 

 channel. The observations taken during this experiment showed a mean increase on 

 those of previous experiments made under the same initial conditions of 1'2 F., the 

 rate of fall of temperature with pressure in the wiredrawn steam being the same as 

 that indicated in previous experiments. 



