MEASUREMENT OF TEMPERATURE. 
219 
bulb. Thus :—5 '2 cm. = 15 (508 — 340)/(508 — 18). The volume of this portion 
( 5'2 cm.) (by curve constructed from calibration data) is '030 cub. cm. This has 
to be deducted from V 0 , the volume of the bulb, and added to v, the volume at air 
temperature. 
The volume of the bulb up to the platinum-copper junction of the electrode is 
calculated, assuming that air satisfies Boyle’s Law, from the observations ( 20 ) and (26), 
both of which give the same result, Y 1 = 63Ml c.c., V 0 = 63’29 c.c. 
In our case V 0 = 63'29 — '03 = 63'26 c.c. 
The glass expansion factor corresponding to pt = 508'4 is taken from the 
curve whose equation is given in the section on the expansion of hard glass, 
p. 168, Y = V 0 (l + yd) — (63'26) (1'0124). Small errors are less likely to be intro¬ 
duced if this correction is applied last of all to the value of 9. 
To calculate the volume at air temperature % ( vj6 '):—- 
The volume from division x = 9 of the scale S, and x = 0 of the scale FG, 
to the platinum-copper junction of the capillary tube electrode was determined by 
previous calibration to be 0'708 c.c., and is assumed to be, at the temperature of the 
air, A = 18'2 ; & = 291T. 
The mean value of x, the reading of the gauge in Observation (5), is 7' 21 . 
The corresponding volume is (7' 21 ) ('0232) = T67 c.c. 
Thus v — '70S + T67 + '030 = '905, and v/ff = '003110. 
Mercury was allowed to run out by way of P 3 into a beaker till the difference 
between the pressures of the internal and external air came within the range of the 
H 0 SO 4 gauge. The weight of the mercury and beaker was W = 244'902, that of the 
beaker 31'220. The same beaker was used in all the weighings here given. 
Since the value of the temperature of the bulb A observed with the mercury 
thermometer G cannot be correct to more than 1 in 5000 ( 1/20 degree), it is needless 
to reduce the weight to vacuo or apply any of the other small corrections. The 
density of the mercury at 17°'55 C. being 13'553 grms. per c.c., the volume of 
213'682 grms. is 15'668 c.c. Since the mercury stood at x — 9 2 just before it was 
allowed to run out, we must add (' 2 ) (’0127) c.c. to reduce it to x = 9. 
Thus the auxiliary volume was 15'770 c.c. at a temperature 
* 
17°'55 + 272'90 = 290°'45 C. by air thermometer. 
Thus v/6' = -054290 ; ff/ff = '003110 ; 2 (v/0') = '057400. 
The acid stood at 2'30 in the gauge when the pressure was the same in either limb, 
and by experiment it was found that the reducing factor 0'136 was required to give 
the pressure correction in terms of mercury. Thus the required correction in 
Observation (5) is (7'21 — 2'30) '136 = '670. 
The barometer reading reduced to centimetres is 77'659 cm., and the temperature 
16°'2 C. ■; correction for temperature,— '228 cm. ; correction for level and capillarity, 
+ '045 cm. 
2 f 2 
