The pressure on the valve from either side will not equal the pressure registered on the gauges. To the latter pressure must
176 SOLUTIONS
be added the hydrostatic pressure of a column of gas pgh. Since the density of CO₂ is greater than that of H₂, the pressure on the valve from the left will be greater than from the right, and after the valve is opened part of the carbon dioxide will pass into the vessel containing hydrogen.
In the second experiment the pressure-gauges will be underneath. In this case the pressures at the valve will be pgh less than those registered by the gauges. If the pressure-gauges read the same, then the pressure of hydrogen on the valve is greater than that of the carbon dioxide, and when the valve is opened, part of the H₂ will pass into the vessel containing CO₂.