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21387Re: [new_distillers] Re: Specific Gravity

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  • Robert Thomas
    Aug 12, 2006
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      Well said Harry.
      It can lead to a big can o' worms if you start getting too fancy:
      there is the heat of mixing, which will change your readings; is your
      thermometer measuring accurately; is the mixture homogeneous; do the
      fusils in the distillate alter the surface tension; how did you clean
      the hydrometer; even simple stuff, like are you reading it correctly
      (top/bottom of the meniscus - depends on make).

      It ain't worth worrying about! relax, have a dram, put your feet up!

      --- Harry <gnikomson2000@...> wrote:

      > Ok, I thought I may be able to give a simple answer to a simple
      > question, being as how this is new_distillers & we don't want to
      > confuse people with highly technical stuff that really ain't
      > necessary to hobby distilling.
      > However, it appears I was hoping for too much. So everyone wants
      > this thing to be accurate to the nth degree (why I don't know. It
      > don't matter a hill o' beans in our small setups).
      > First of all, the Specific Gravity of Ethanol or Water is variable,
      > depending on the prevailing temperature of the liquids at the time
      > of measurement. So any declaration of the 'SG' of these substances
      > should really be made with an attached reference to the temperature
      > of the samples. For instance, the density of water at 4�C is 1
      > The specific gravity of pure ethanol is 0.7939 and that of
      > pure water is 1.000.
      > So here's a problem for you to ponder...
      > Determine the expected density of 70% v/v ethanol in water, if the
      > volumes were additive. Compare the specific gravity obtained to
      > actual specific gravity of 0.89. Does the solution contract or
      > expand on mixing? Consider 1 ml of the 70% ethanol mixture. It
      > contains 0.7 ml ethanol and o.3 ml water if the volume on mixing is
      > assumed additive.
      > Mass of the 0.7 ml ethanol = Volume Density = 0.7 x 0.7939 = 0.5557 g
      > Mass of the 0.3 ml water = 0.3 g
      > Total mass = 0.5557 + 0.3 = 0.8557 g
      > Density = Mass/Volume = 0.8557 g/1 ml = 0.8557 g/ml
      > Since the actual density is greater than the expected density, the
      > mixture contracts.
      > For all intents & purposes, the calculations that Gert Strand
      > provided on the link I gave, are adequate for our hobby needs. If
      > you want to split hairs, or get laboratory-grade calculations &
      > results, then by all means, do the math to the nth degree. The
      > margin of error over the calcs that Gert & I gave are so small as to
      > be irrelevant.
      > We are looking for simple calcs (at least the original
      > poster/questioner was). Lab-grade 3 decimal point correctness is
      > not warranted in this situation. But of course there will always be
      > those who demand to know that if a thing is white, then just what
      > shade of white is it? And there will always be some who wish to
      > take issue with my generalisations. Oh well...life is short.
      > Slainte!
      > regards Harry


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