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Proceedings of the Royal Society 
2. On a Sulphurous Acid Cryophorus. 
By Sir W. Thomson. 
{Abstract.) 
The instrument exhibited to the Royal Society consisted of a 
U-shaped glass tube stopped at both ends, containing sulphurous 
acid liquid and steam. The process by which the sulphurous 
acid is freed from air, which was partially exhibited to the Royal 
Society, is as follows : — 
Begin with a glass U tube open at both ends, and attach to each 
a small convenient, very fine, and perfectly gas-tight, stop-cock. 
Placing it with the bend down in a freezing mixture, condense 
pure well-dried sulphurous acid gas direct into it from the generator 
till it is full nearly to the tops of the two branches. Then close the 
stop-cock, detach from the generator, and remove from the freezing 
mixture. Holding it still with the bend down, apply gentle heat to 
the bend, by a warm hand or by aid of a spirit-lamp, so as to produce 
boiling, the bubbles rising up in either one or the other of the two 
branches. After doing this for some time let the bend cool, and 
apply gentle heat to the surface of the liquid in that one of the 
branches into which the bubbles passed. With great care now open 
very slightly the stop-cock at the top of this branch, until the liquid 
is up to very near the top of the tube, and close the stop-cock before 
it begins to blow out. Repeat the process several times, causing the 
bubbles sometimes to rise up one branch, and sometimes up the 
other. After this has been done two or three dozen times, it is 
quite certain that only a very infinitesimal amount of air can have 
remained in the apparatus. When satisfied that this is the case, sink 
the bend once more into a freezing mixture, and with a convenient 
blow-pipe and flame melt the glass tube below each stop-cock so as to 
hermetically seal the two ends of the U tube, and detach them from 
the stop-cocks. This completes the construction of the sulphurous 
acid cryophorus. 
The instrument, if turned with the bend up and the two sealed 
ends down, may he used as a cryophorus presenting interesting 
peculiarities. 
The most interesting qualities are those which it presents when 
