Equivalents of Oxygen and Hydrogen. 623. 
6. Temperature. 
The most important temperature to record was that o£ the 
water-jacket o£ the gas-burette. This was taken by a 
thermometer (graduated in \ degree) near the exit of the 
water. This thermometer had been compared with a 
standard that had been tested at the Keichsanstalt, and 
showed, over the atmospheric range of temperature, only 
irregular variations amounting to about o, 06 as a maximum. 
The standard itself was tested at the freezing and boiling- 
points and found to be exact, as stated in its certificate. 
The water-jacket sometimes rose and sometimes fell in 
temperature during an experiment : in unfavourable cases 
as much as 1*5 degrees ; sometimes only one or two tenths 
of a degree. The final reading, taken immediately after the 
outflow of mercury had been adjusted, might sometimes be 
uncertain to the extent of o, 04 or o, 05 : this is probably 
the most serious error in the experiments ; it affects the 
reduction of the gas both directly and through the vapour- 
pressure of w^ater, so that an error of o, 05 means about 
a55o t0 3555 on the result * 
The other temperatures noted were : — 
(a) Barometer : owing to the rapid fluctuations in room- 
temperature, the mercury of the barometer may at times 
have been a degree or more different from the attached 
thermometer. This would affect the pressure by g^. 
(b) Cadmium cells : the influence of this is very small, 
and has been allowed for above. 
(c) Air. 
(d) Coulometer : a correction has to be made if the tem- 
perature of the coulometer is not the same at the beginning 
and end of the experiment. The coulometer itself was 
calibrated for volume, so that the amount of gas in it could 
be determined. If this was say 2 c.c, and the burette held 
190 c.c, one degree makes a difference of 
1 J>_ 1 
290 X 190 ~ 28,000 
in the volume of gas. 
The temperature of the coulometer was allowed to fall 
after the experiment to nearly the same level as before, and 
the mercury then adjusted : the above correction was con- 
sequently always small. 
The uncertainties introduced by fluctuations of tem- 
peratures are certainly the most important, and show that 
the results given below are about on the limit of the accuracy 
obtainable by this apparatus. 
