hist-brewing: Hydrometers / iodized salt

William Arthur Millett wmillett at fractal.com.br
Tue Jan 18 15:54:54 PST 2000

Hydrometers have been in use for ages. They were described perhaps for the
first time around 290 AD by the Alexandrian mathematician Pappos (Papus?).
In 410 AD a bishop Sinesius mentions, in a letter to the philosopher
Hypathia, the scale hydrometer. Judging by what he says, it may be inferred
that the instrument was new to him.

It may not be possible to determine who invented it, but in any case, it is
a very old invention. It underwent considerable improvements since the 17th

Although hydrometers were known and used in Sir Kenelme Digby's time (17th
century), he apparently preferred eggs as a means to estimate specific
gravities of honey and water solutions. In one instance he mentions "take
two new-laid eggs (...) and put them whole into the bottom of your cleansed
liquor; and if it is strong enough, it will cause the eggs to ascend upward,
and to be on the top as broad as sixpence (...) " A sixpence in his time
would have had 21 mm in diameter (a bit over 3/4 inch)

By the way - iodized salt is salt with a few ppm of sodium iodate (iodate is
iodine in one of its higher oxidation states) added to prevent goiter
(swelling of the thyroid glands through lack of iodine in the diet).

All the best,


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