534 
Proceedings of the Royal Society 
\- 
— 
I3TI 
IS!— 
- 
-J=T 
IF 
— $- 
Z-3TI_ 
-R — 
-3& 
Fig. 2. 
bottles and pumice tubes, 
&c. Then make the junc- 
tion at Q, close the stop-cock 
S and open R very gently 
taking care not to let air 
be sucked in by the safety 
tube of the generating ap- 
paratus. * Continue until liquid sulphurous 
acid is seen in the long vertical branch, 
about the top of the freezing mixture, then 
close the iron stop-cock E, disconnect at E, 
and remove from the freezing mixture (but 
beware of Professor Guthrie’s cryohydrates). 
(4.) Now, place the instrument with the 
long straight parts of the tube nearly hori- 
zontal, but sloping slightly upwards towards 
L, and by a hand or spirit lamp properly 
applied, boil the liquid, the stop-cock L 
being still closed. After boiling for some 
time cause the liquid to occupy the whole 
space from T to its free surface, then very 
carefully open the stop-cock L slightly, being 
ready to close it quickly and prevent the 
escape of any of the liquid in case of sudden 
ebullition. Repeat this process over and 
over again two or three dozen times, so as 
thoroughly to remove air or other gases more 
volatile than sulphurous acid from the liquid. 
To as much as possible remove water or any 
* One of the sulphuric acid wash-bottles must be provided with a safety 
tube with overflow bulb. An ordinary pipette with its stem fitted into the 
india-rubber stopper of the bottle will serve for the purpose. 
