418 
DE. F. P. BURT AND DR. E. C. EDGAR ON 
time interval in question was in most cases rather greater, since the hydrogen took 
longer to obtain. On the other hand, the correction for the imprisoned bubble was 
probably a little smaller. The presence of this bubble had escaped observation in the 
early part of the research, owing, perhaps, to the fact that the mercury in the pipette 
was very clean and therefore trapped a smaller quantity of gas. # With long continued 
use and contact with rubber tubing, inevitable slight fouling occurred.t 
That the average volume of the imprisoned bubble was increasing very slightly 
during the later stages of the research, was proved by actual measurement. Both 
these opposing errors may therefore have been smaller in the earlier series. Taking 
into account the very close agreement of the means it seemed fairest to apply the same 
“ contraction ” correction throughout, and to reduce the means of all four series by 
6 parts in 100,000. Collecting all the results we have :— 
Series 1. j Series 2. 
Series 3. 
Series 4. 
2-00294 2-00292 
2-00292 
2-00301 
±0-00002 +0-000014 
+ 0-00001 
±0-00002 
Corrected for imorisoned bubble . 
2-00301 2-00299 
2-00299 
2-00301 
Corrected for “ contraction ”. . . 
2-00289 2-00287 
2-00287 
2-00289 
The arithmetic mean of the ratios in the last line is 2'00288, and the corresponding 
atomic weight of hydrogen is 1'00772. 
Fifth Series. 
Since the magnitude of the “ contraction ” correction was a little uncertain, a fifth 
series of determinations was undertaken. In this series no measurement was made 
until the pipette had been in ice for at least three hours. The gases were made and 
purified exactly as in series 4, and the trapped hydrogen bubble was removed before 
the oxygen filling. To eliminate variations in the temperature of the mercury in the 
exposed portion of the manometer, a small subsidiary bath, constructed of the two 
halves ot a short brass cylinder, mounted on a split cork, was fitted to the manometer 
tube in this region. This bath was filled with powdered ice immediately before each 
reading was made. By a modification of procedure on the second day the two final 
settings were made one immediately after the other so that there was no need to re-ice 
the baths. As soon as the first setting was finished, the hydrogen residue, previously 
accumulated in the collector, was at once admitted, and the necessary adjustment made 
by running out mercury. Of the thirteen experiments in this series, one, No. 6, was 
* Before its introduction into the apparatus the mercury was purified from foreign metals by distillation 
and by washing with mercurous nitrate solution, and was finally dried by heating to 120° C. 
f The tubing used was of a special kind designed to resist attack by mercury. 
