search  current discussion  categories  kilns & firing - shelves & furniture 

sodium silicate and degrees twaddell

updated mon 30 sep 02


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