The Pitch Drop Experiment

[Nick Clarke 3Participant @nickclarke3]

Thanks for your comments Alan, however I don't think they affect the now commonly held view that Glass is not a supercooled liquid.

Taking the first one – I quite agree that glass is amorphous, but that as an amorphous solid the molecules do not flow and rather than having a high viscosity as would be the case above the glass transition temperature, the molecules are joined together but not in a regular pattern.

Working at a more practical level – lenses and ancient glass objects would be expected to show some flow and windows would not only be thicker at the bottom but would exhibit flow over frames and the nails holding the panes into the frame, which I have never seen suggested. Hence I am of the belief that the thicker at the bottom concept is due to manufacturing rather than flow. The comment one sometimes sees that glass becomes more solid with age and very old objects are less likely to flow also appears to be at variance with the facts as it is the oldest building glass that is said to exhibit the most flow.

Referring to your second point, that the glass in your lab had to flow to change shape. You have explained how this cannot be the case with wood or steel but both of these materials do change shape and while I agree that it is not due to flow – I cannot agree that glass is a special case and has bent for a unique reason.

Please consider what I have written – I am trying to summarise information garnered over the last 25 years or so since the first arguments against the 'glass is a supercooled liquid' theory were discussed in the scientific press. However it is the accepted theory at present – but the one thing I hope is not to fall out with anyone here, but rather to present accepted and justified (most important that!) scientific thought as appropriate.

Take care,

Nick

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