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degrees baume to specific gravity conversion

updated sun 22 aug 99


Bruce Girrell on sat 21 aug 99

Ivor Townshend asked:
> Does anyone have a reliable rule for converting Baume to Specific
> Gravity? Can they also give me a reference to justify it?

>From the Handbook of Chemistry and Physics, 51st edition (which is old, but
these things don't change too often) by The Chemical Rubber Company (whose
handbooks are standard references for universities, research depts., etc.):

Baume - There are two kinds in use: heavy Baume for liquids heavier than
water and light Baume for liquids lighter than water. In the former, 0
degrees corresponds to a sp. gr. 1.000 (water at 4 deg. C.) and 66 degrees
corresponds to a sp. gr. 1.842; in the lighter than water scale, 0 degrees
Baume is equivalent to the gravity of a 10% solution of sodium chloride and
60 degrees Baume corresponds to a sp. gr. of 0.745. For Baume degrees on the
scale of densities greater than unity, the following equation gives the
means of conversion:

Sp. gr. = m /(m-d) where

m = 145 (in the United States)
m = 144 (old scale used in Holland)
m = 146.78 (New scale or Gerlach scale)
d = Baume reading

So I guess your first task is to find out which kind of Baume hydrometer you
have. That should be easy - just throw it in a glass full of alcohol. If you
have the wrong kind of hydrometer it will read on scale, probably about 26
degrees for 100 proof vodka. If you're lucky you have a hydrometer that
reads between about 1.38 to 1.84 sp. gr. - just the right range.

The second task is to choose an m value, since there are three of them. I
was curious which m value they used for the 66 degrees = sp. gr 1.842, so I
back calculated and got a _fourth_ m of 144.3848! Maybe your hydrometer is
marked with the word Gerlach or something else that would help you decide.

Bruce "feeling a little baume (balmy) today" Girrell