Roger Graham on sun 29 sep 02
Often wondered about this myself but didn't know where to look. But this is
the computer age with magnificent search engines... yippee. So I tried the
search engine Google, and entered "Twaddell + sodium silicate". And sure
'nuff, there's an answer. Four links came back, the vital one headed
"Echelles de densite des liquides" (Translate this page).
Paraphrasing what it says, degrees Twaddell is (was) a scale used in
England for expressing densities of liquids more dense than water. The value
in degrees Tw would have been given by
Degrees Tw = 200 x (Specific gravity of the stuff - 1)
They give an example. If your sodium silicate (or whatever) had a density
value of 75 degrees Tw, the maths would be:
75 = 200 (SG -1) (where SG is the specific gravity of the stuff)
So (SG-1) = 75/200 = 0.375
Thus SG = 1.375
That is, 75 degrees Twaddell is the same as a specific gravity of 1.375
Learn something every day!
Roger Graham
http://members.optusnet.com.au/~rogergraham
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