This is a link to an old British Pathe short film of the assay being undertaken at Goldsmiths Hall, London in 1951.
You will need 'Adobe Flash 10' to view this short film, this one does have sound.
If you do not have this application just follow the prompts to download.
http://www.britishpathe.com/record.php?id=47120
Trev.
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