Till: THKKMODYNAMICAL PROPERTIES OF SI' I'KIHIKATI.I > MKAM. II 



drawn steam was suggested to the author by Professor REYNOLDS. The direct 

 determination of the temperature hy the insertion of the thermometer in the steam 

 would have increased the difficulty of obtaining correct temperature readings 

 considerably, on account of the many corrections necessary. 



SECTION VII. Method of Experiment. 



It was found necessary in beginning an experiment to warm the apparatus gently, 

 as the orifice plate frequently cracked with sudden heating. When sufficient steam 

 was passing through the apparatus and the required pressures attained, the admission 

 valve was fixed sufficiently wide open to allow the maximum quantity of steam per 

 minute required during the experiment to flow through it, and at the same time 

 allow a sufficiency for drainage. 



The pressure in the steam reservoir was then kept constant during the experiment 

 by opening or closing the valve in the drain pipe according to the quantity required 

 through the orifice. The opening in the valve V s beyond the orifice was then fixed 

 so as to give any desired constant pressure to the wiredrawn steam ; the temperature 

 of the oil bath was then raised to equality with that of the wiredrawn steam, and 

 the temperature in the steam jacket adjusted to equality with that in the oil bath 

 by a few observations with the galvanometer. It was then necessary to wait for 

 about 2 hours before a steady condition could l)e obtained ; during this period the 

 temperature of the wiredrawn steam would rise slowly, causing the temperatures in 

 the oil bath and in the steam jacket to be continually readjusted. 



After about 3 hours from the commencement of the experiment, the temperatures 

 l>ecame sufficiently steady to allow readings to be taken. Observations of the 

 temperatures in the steam reservoir and in the oil bath, and of the pressure l>elow 

 the orifice, are then taken as often as possible, intervals of 2 to 5 minutes elapsing 

 between successive readings, the mean of successive readings taken over a period of 

 from 15 to 30 minutes being taken as the correct reading, as shown in Table I. 



The method of taking a reading is as follows : The pressure being steady on 

 either side of the orifice, the oil in the bath, which is kept at a slightly different 

 temperature from that of the steam, is heated or cooled slowly, as required, during 

 which period the galvanometer is brought several times into circuit with the junction 

 in the steam, until the deflection of the needle ultimately vanishes. When this 

 point is reached the temperature is noted on the oil bath thermometer ; immediately 

 this is read the galvanometer is brought into circuit with the junction in the steam 

 jacket, and any deflection of the needle noted. These are entered along with the 

 it nipcrature in the reservoir and the pressure below the orifice in the following 

 tal>le, the column headed II S giving the reading R before circuiting, and S the 

 deflected reading ; if R S is positive, the steam in the jacket is hotter than the 

 wiredrawn steam, and vice vend. 



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