1916-17.] The Adsorption of Sulphur Dioxide by Charcoal. 163 
dioxide owing to rapid evaporation into the atmosphere, and was obviated 
by joining on a mercury bubbler to the delivery tube from the calori- 
meter. When the mouth of the calorimeter was closed the gas bubbled 
through this and the atmosphere above the liquid soon became entirely 
gaseous sulphur dioxide, and the temperature remained steady at that, 
corresponding to (say) 0*5 mm. more than the barometric pressure.* 
The greatest difficulty was the adjustment of the temperature of the 
freezing mixture round the vacuum vessel. The observations were taken 
during a spell of hot weather, which no doubt contributed to the steady 
rise in temperature of the mixture from —10° C. The variation of the 
leak due to radiation inw*ards showed that the liquid sulphur dioxide was 
very sensitive to changes in temperature of the surrounding bath. The 
leak varied also with the level of the dioxide in the calorimeter. In 
itself the leak was small, but when the measurement was spread over two 
or three hours it soon amounted to a considerable percentage of the 
volume of the gas evolved during the experiment. As a result, observa- 
tions of the leak had to be taken from (say) two hours before the gas 
was let in to be adsorbed till some time after the adsorption was 
adjudged complete. The author is convinced that the substitution of a 
freezing mixture for a bath of the calorimetric liquid itself — as used 
by Dewar — was a grave mistake, and impaired the ease and accuracy of 
the observations. 
The apparatus made and devised by the author for the study of ad- 
sorption is shown in fig. 2, and is essentially a constant- volume apparatus. 
It consisted of a large bulb whose one end was attached to the ground- 
glass join to which fitted the charcoal bulb part of the calorimeter. The 
other end joined on to a capillary tube passing into ordinary quill tubing 
containing a fine tip of blue glass. From below this ran a side tube with 
a tap connecting with the mercury pump and the gas reservoir.]* 
The main tube continued downwards, then upwards parallel to the blue- 
point tube, and constituted with its connections a manometer, pressure 
readings being taken in the mirror scale behind. The volume from the 
blue point (marked b in the figure) to the tap of the charcoal bulb was 
found from the weight of mercury of known temperature required to fill 
it ; and the volume from the tap to the bulb (including the hole in the 
tap) was similarly found before joining on the filled bulb to the capillary.]; 
* It would have been possible by means of a tap to adjust the mercury so that the 
pressure was always (say) 78’0 cms., and so keep the dioxide at a fixed temperature. 
f A two-way tap above the charcoal bulb would have been simpler. 
I A change in volume on joining of Off c.cm. would affect all the calculated values of 
the amount adsorbed 0’03 per cent., and the change must have been less. 
