632 
MR. H. B. DIXON OX CONDITIONS OP CHEMICAL CHANGE 
and the first explosion tube a drying tube packed with phosphoric oxide was placed; 
the last explosion tube was connected with a delivery tube, opening under strong 
sulphuric acid in a wash-bottle. The mixture of gases was then forced through the 
tubes, and when about a litre had been allowed to escape from the wash-bottle, the 
counterpoise of the gasholder was so adjusted that the pressure in the tubes was a 
little less than the pressure of the atmosphere. A fine Bunsen flame was then brought 
to bear upon the capillary portions of the tubes until the sides fell in under the 
external pressure, whereupon the glass was melted and drawn out. This operation 
was found to be far from easy ; more than half the tubes so charged were fired during 
the sealing, owing to the contact of the insufficiently dried gases with the heated 
glass. I tried in vain to seal up damp tubes filled with the same mixture; the 
gases always exploded when the fine glass tubes got red hot. About half the 
samples of carbonic oxide and oxygen sealed up with phosphoric oxide were 
unaffected when a succession of sparks from a coil was passed through them a few 
hours afterwards.'" The other half ignited after the discharge had been passing for a 
few seconds. In some cases this appeared to be due to'some phosphoric oxide having 
been shaken on to the platinum wires, which gave off moisture when heated by the 
discharge. In other cases, I believe, the ignition was due to the platinum wires 
themselves, when heated by the discharge, giving up occluded hydrogen, which uniting 
with the oxygen present supplied the steam necessary for the combustion. 
An easier method of drying the gases was next adopted with complete success. A 
glass tube about 600 millims. long was closed at one end, and at a point 100 millims. from 
the open end it was bent at an angle of 60°. Near the closed end two long and thick 
platinum wires, ending in balls of platinum about 2 millims. in diameter, were fused 
through the glass. Between these balls sparks could be passed from a jar or a coil 
without appreciably raising their temperature. The bent tube was heated and filled 
with hot mercury. The mixture of carbonic oxide and oxygen was then introduced from 
the gasholder by a fine glass tube passing down through the mercury in the shorter 
arm. When the longer arm was nearly filled with the mixture, a freshly packed 
stick of phosphoric oxide was introduced into the gases, and the open end closed with 
a caoutchouc stopper. The mixture of gases was thus separated from the ah' by some 
six or eight inches of mercury and the caoutchouc stopper. After standing for twenty- 
four hours, the mixture was unaffected by a torrent of sparks from a powerful coil. In 
one of these tubes I have submitted the gases to a pressure of 800 millims., and passed 
a discharge without igniting them. On passing up some water through the mercury 
by a pipette and allowing the vapour to diffuse, the mixture was rendered explosive. 
* Four of these tubes were exhibited before the Chemical Section of the British Association at Swansea 
in 1880. When tested with sparks from a Leyden-jar no action was observed; with a discharge from the 
coil the wires became red-hot, but the gases did not explode. 
I gratefully acknowledge the valuable help given me by Mr. S. E. Miller, laboratory assistant at 
Christ Church, in charging these tubes. 
