21387Re: [new_distillers] Re: Specific Gravity
- Aug 12, 2006Well 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 simpleg/ml.
> 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 4ï¿½C 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.
> regards Harry
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