PROF. C. FRKWEN JENKIN AND MR D. R PYK ON THE 



"" t 



liM ,ll y coils of No. 16 S.W.G. Eureka wire, insulated with vulcanized indiarubber 



Lu d directly on to the coils of the evaporating pipe, were tried; these 



perfectly Each coil was about 50 yards long, had a resistance of about 



To InT L Juld absorb 1000 watts, taking 10 amperes from the 100-volt power 



m ,ins There are three such coils in the larger and two in the smaller calorimeter. 



Jfcomtmtflt of the Electrical lfa*-The electrical power entering the calon- 

 meters was calculated from the measured resistances of the heating coils and the 

 ol*erved E M F across their terminals. The E.M.F. was measured by means of a 

 Siemens millivoltmeter with fine pointer and mirror, which was calibrated against a 

 cadmium cell with N.P.L. certificate. The scale is divided in single volts and ^ vol 

 can be accurately estimated. Two of the coils in the large calorimeter were always 

 connected, when in use, on the full supply voltage (100), and the third was used in 

 series with an adjustable resistance. The voltmeter has a two-way switch so that 



the two E.M.Fs. could be read successively. Read- 

 ings were taken every minute throughout the tests. 

 At the full voltage of 100 an error of 1 volt means 

 an error of '2 per cent, in the power. At the lowest 

 readings, 30 volts, an error of '1 volt means an error 

 of '6 per cent, in the power. The resistance of each 

 heating coil was measured before the tests were 

 begun by a bridge which was checked against a 

 standard ohm with N.P.L. certificate. The resist- 

 ances were measured again after the tests were 

 completed and had not altered appreciably. No 

 temperature correction was made as the coils were 

 made of Eureka, but corrections were made for the 

 resistance of the leads. 



The temperature measurements were all made 

 with Eureka-copper thermo-couples. The couples 

 were made of No. 22 gauge double cotton and india- 

 rubber-covered Eureka and copper wire, all cut from the same coils, soldered together 

 at the ends. The couples used in the baths for measuring the temperature of the 

 circulating liquid were put into rubber tubes, the bare ends projecting about ^ inch. 

 The couples used for measuring the temperature of the CO 2 were held in the special 

 fittings shown in fig. 15, so that the bare wires projected into the CO 2 about 

 lj inches. The wires were carried through the gumnetal plugs in fine rubber tubing 

 (bicycle valve tubing). The holes in the gumnetal were tapered and small brass 

 beads were soldered on the wires, so that when the wires were drawn back the beads 

 jammed in the holes. This simple device made an insulated joint which was gas-tight 

 under the highest pressures used (1100 Ibs. per sq. inch). 



Preliminary calibrations showed that the relation between the E.M.F. of the 



Fig. 15. 



