The apparatus for equilibrium relative humidity determination
is shown in Fig. 1. The sample was placed in
a steel sample container, with a stainless-steel mesh
thimble maintaining adequate air space in the centre at
the top for the dewpoint sensor. Apart from the space for
the sensor, the container was "lled as full as possible with
the sample. The container lid, into which the dewpoint
sensor was "tted, was then screwed on to the top of the
sample container, with the threads sealed with polytetrafluoroethylene
(ptfe) thread tape. The whole sample container
was placed in a precision temperature-controlled
oven (stable to better than 0.13C) at ambient temperature.
The volume of air in the sample container was
approximately 1/50 of the volume of tea, so that any
change in moisture content of the air had negligible e!ect
on the moisture content of the sample.