Combination of Hydrogen and Chlorine. 1 2 1 



the tap of the pressure tube is opened for a moment and 

 then closed. The height of the mercury in the tube gives 

 the pressure in the bulbs. By having the gases in the bulbs 

 slightly below the atmospheric pressure a little nitrogen 

 from the pressure tube enters the bulb and no chlorine 

 escapes into the pressure tube. After firing at a suitable 

 temperature the temperature can be reduced to the same 

 point as before. Then on opening the tap of the pressure 

 tube the rise of mercury indicates the diminution in volume 

 of the exploded gases. If hydrogen and chlorine united 

 without contraction to form an equal volume of hydrogen 

 chloride gas, and if the hydrogen united entirely with the 

 chlorine and not with the oxygen at all, then no alteration 

 in volume would result from the explosion. 



However, on firing the well-dried mixture of the three 

 gases by a spark at ordinary temperatures, a cloud is formed, 

 and a considerable contraction is shown by the pressure 

 tube. We have found a contraction of over 10 per cent 

 of the original volume of gases — due partly to the formation 

 and condensation of steam, and partly to the formation of 

 hydrogen chloride and to its solution in the water condensed. 

 We say that the condensation is partly due to the formation 

 of hydrogen chloride, because we have found that however 

 carefully the bulbs and the gases are dried, there is a 

 sensible contraction when hydrogen and chlorine combine 

 in a glass vessel. This contraction is rather over 1 per cent 

 of the original volume. We have varied the apparatus and 

 the manner of working, but we always find nearly the same 

 result — whether the gases are exploded or whether they 

 combine gradually in diffused light. 



The fact that the hydrogen divides itself between the 

 chlorine and the oxygen is proved by the large contraction, 

 by the cloud, and by the visible drops which condense on 

 the surface of the bulb. 



Proof of another kind is afforded by the fact we have 



