THK THERMODVNAMICAL PROPEBIDB OF SUPERHEATED STEAM. 5 



SECTION III. Preliminary Experiments. 



After completing the experiments on the quantities of steam discharged from an 

 orifice, as described in the paper before referred to, at Professor REYNOLDS'S advice, I 

 made some experiments on the temperatures of the wiredrawn steam, using for this 

 purpose a thermo-electric junction inserted in the steam, and a second similar 

 junction in the same circuit immersed in an oil bath, the temperature in which (given 

 by a thermometer) may be adjusted to have any required value, both junctions being 

 in circuit with a galvanometer. The remainder of the apparatus was unaltered. 

 When both junctions are at the same temperature no deflection of the galvanometer 

 needle will be observed, and hence the temperature in the oil could be adjusted to 

 that in the steam. 



The object of these experiments was to observe to what extent the results would 

 be aftected by radiation. 



The results obtained were very useful in this direction. The amount of lagging of 

 the channel containing the wiredrawn steam was altered in different experiments 

 made under the same initial conditions of pressure and temperature above the orifice, 

 the comparison of the results showing that radiation affects the results to a very 

 great degree, even with a fair amount of lagging. 



The fall of temperature in the wiredrawn steam in any experiment was almost 

 proportional to the difference of pressure, a result which is in accord with those of 

 later experiments. 



The results of these preliminary experiments showed clearly that before any 

 accurate work could be done on the temperatures, the effect of radiation must be 

 eliminated, and in the construction of the apparatus as finally used (see Section V.) 

 the manner in which this was effected will be described. 



SECTION IV. Nature of Orifice used. 



In the paper on the " Flow of Saturated Steam " it is shown that steam flowing 

 through a circular orifice in a glass plate expanded according to the adiabatic law. As 

 a glass plate would also diminish materially the passage of heat by conduction from 

 one side to the other of the orifice, it has many advantages over other materials 

 for wiredrawing experiments in which the difference of temperature on the two sides 

 of the orifice may be considerable, sometimes amounting to 70 F. in the following 

 experiments. 



The orifice used was a circular one of about -^ inch diameter drilled in a piece of 

 plate glass ^ inch thick. This orifice plate O, is fixed between two cast-iron flanges, 

 F and F, figure 3, the joints being made by copper rings ; the flanges are connected 

 by three bolts ^\ inch in diameter, passing through holes in the flanges ^ inch 



