396 
DR. F. P. BURT AND DR. E. C. EDGAR ON 
removed by four hours’ exposure to charcoal cooled in liquid air. The storage bulb 
was connected to the U-tube, M, containing charcoal. This tube had been 
prepared in the following way : ll'5gr. of charcoal, made from cocoa-nut shell, were 
introduced into the tube in fragments the size of a pea. The tube was exhausted by 
a water pump, and then heated in a glycerine bath to a temperature of 240° C. Dry 
hydrogen was next admitted and then pumped out again, and this operation was 
repeated several times. Finally, the tube was exhausted at 240° C. and sealed off. 
When cold, dry air was admitted, and the tube was immediately sealed to its connec¬ 
tions on the apparatus. The observations of Dewar ( 8 ) and, more recently, of Claude ( 9 ), 
indicate that, in the absence of helium and neon, exposure of hydrogen to charcoal 
at liquid air temperatures should prove a very efficient method of removing other gases. 
Hydrogen itself is absorbed to a considerable extent. According to the measurements 
of Claude, 100 gr. of charcoal, cooled to —195°'5 C., can take up about 20 c.c. of 
hydrogen before the pressure reaches a tenth of a millimeter of mercury. Five litres 
of nitrogen ai’e required to produce a similar pressure, whilst oxygen is still more 
readily absorbed. When cooled in liquid air and put in connection with the 2|--litre 
storage bulb, containing hydrogen at atmospheric pressure, the 11‘5 gr. of charcoal 
in our U-tube reduced the pressure to about half an atmosphere. By closing the 
storage-bulb tap and admitting hydrogen from the electrolysis vessel and drying train 
through the cross-tube, N, the charcoal vessel was rapidly filled to atmospheric pressure. 
Electrolysis was then continued until sufficient hydrogen had been passed over the cooled 
charcoal to charge the measuring vessel. The liquid air vessel was then removed and 
part of the gas from the charcoal was allowed to return to the storage bulb. The later 
fractions were removed by the mercury pump, the train being exhausted at the same 
time. In this way impurities which had been retained by the charcoal were prevented 
from accumulating in the system. A cross-piece, O, carrying a tap connected the 
two limbs of the U-tube so that the train could be pumped out by another path in 
addition to that through the charcoal. A mercury gauge, P, recorded the pressure 
of gas in the system. 
Purification of Hydrogen: Second Method. 
The gas was dried, as before, over calcium chloride and phosphoric oxide, but, in 
some series of determinations, passed first through a tube containing palladium black 
to remove oxygen. After leaving the drying train the hydrogen was made to pass 
through the walls of a heated palladium tube (fig. 2, A). This tube, 10 cm. long, 1 cm. 
in external diameter, and having a wall thickness of about 0'6 mm., was welded to 3 cm. 
of platinum tube of similar dimensions. The platinum was sealed to a glass tube, B, 
which, in its turn, was fused as an inserted join into a wider tube, C, connected at its 
other end with the drying train. The wide tube thus formed a cul-de-sac into which 
the blind end of the palladium tube projected backwards. A short cylinder of quartz 
was slipped over the palladium tube and wound with a spiral of platinum wire, the 
