A few years ago some one at UCSC showed me a demo that was supposed to demonstrate the
increased (yes) viscosity of a gas with temperature. It consists of two copper tubing
spirals connected to a "T". This way natural gas or other may be supplied at equal
pressure. The flames at the other ends indicates the volume of gas flowing through the
tubes, initially equal. If one heats one of the spirals its flame height , counter
intuitively, rather noticeably decreases, while the other is unchanged. Conversely,
cooling one with liquid nitrogen causes its to more than double. All well and good until
one realizes that heating a gas will reduce it's density and therefore, also cause
decreased flame height, at least to a first simple minded approximation. What is it? Any
of you heard of this demo., and what does it "really" demonstrate?