It is still generally believed today (as in the currently published diagram A below) that a mercury barometer contains an absolute vacuum above the liquid, and accordingly there is a condition of absolute zero pressure here, however it is also suggested that there are a few mercury atoms in kinetic motion within this vacuum and which, it is implied, essentially do not generate any pressure on the liquid surface by means of their very rare collisions with it.
A
This assumes that the external atmospheric pressure acting on the surface of the exposed mercury liquid is the only force, acting against the pull of gravity on the liquid in the tube, that maintains the observed level of around 760 mm above the exposed liquid at sea level.
The Torricellian barometer was produced by simply filling the glass tube with liquid mercury and, placing a finger over the open end, inverting and emerging it at an angle into a bowl of the liquid, as in the diagram B below, and then after removing the finger the tube was elevated to vertical.
When this elevation angle reaches the point where the top is at 760 mm above the exposed liquid, with any further elevation the liquid in the tube remains at this level whatever length of tube is used, as indicated in diagram B.
However if this apparatus is taken up a mountain this level will fall in the tube, as in Pascal’s subsequent experiment where he found that at an elevation of around 4000 metres, in the conditions of a lower atmospheric pressure here, a level of around 640 mm was observed in the tube.
From this experiment it was assumed that the reduction in atmospheric pressure was the only determinant on the level of the liquid in the tube and that the volume of vacuum increased accordingly, as is depicted in the longer tube in diagram B below. In other words this implied that the vacuum component had no influence whatever on the level of mercury and that it could freely expand (or contract) in volume.
However it is now proven by experiment, as in this video https://www.youtube.com/watch?v=lpZF88fqrl8 that mercury evaporates rapidly at atmospheric pressure and so in the depicted elevation of a glass tube full of the liquid, and the progressive and consequent reduction of pressure, due to the force of gravity, at the upper surface in contact with the top of the glass tube, evaporation will occur. And with further elevation of the tube, past the 760 mm mark, as in diagram B, the volume above the liquid will be composed of mercury in its gaseous state.
But, with respect to the postulates of the kinetic atomic theory of gases, if this space were ‘full’ of a ‘kinetic’ gas that is composed mostly of a volume of inter- atomic vacuum, i.e. 99.9% of the total, then, as this component by definition can have no frictional or any other influence on the ‘kinetic’ motions of atoms, the high velocity collisions of these, massive, ‘kinetic’ mercury atoms will apply a force of pressure on the surface of the liquid, and in this non-zero, low pressure environment obviously further evaporation should occur and the surface level would eventually subside to that of the surface exposed to atmospheric pressure.
As this obviously does not happen, it is evident that there is a force acting here within the tube to maintain the liquid at this level, and if any volume of vacuum, either inter-atomic or sub-atomic were present, then such vacua, patently, could not generate such a force.
This is therefore indisputable evidence, proof, that the general assumption/belief of scientists, over the centuries, in that Torricelli’s barometer proved the ‘existence’ of a vacuum is false and, in complete contrast it is evident, this is indisputable proof, that no vacuum, either inter-atomic or sub-atomic, can possibly be present here, and that accordingly there can be no ‘kinetic’ motion of atoms in such an ‘empty space’.
