Here is an interesting dilution
If I mix 1 gallon of 80 proof at 60F
and 1 gallon of water at 60F
What do I end up with?
The answer is 2 gallons of 40 proof.
Any comments?
For those who have not done dilutions, please follow this thread to find out why this looks so simple.
Reply:
Comment: what's the point of this post??
Reply:
Ahhhh..... trick question. Like ""what's the airspeed of a sparrow bearing a coconut?"
Reply:
You'll have less than 2 gallons due to contraction.
Reply:
How about... don't use volume for dilution, use weight.
Reply:
I dilute each bottle individually with the timed pouring method I used as a bartender, then taste test every bottle I fill. If it seems a bit weak, I add some undiluted high proof spirit with an eyedropper. If it seems strong, I consider that a bonus for the consumer. Truly a handmade, craft produced liquor.
I can only fill 23 bottles a day before I fall asleep on the floor.
Reply:
Jedd, you are wrong, but on the right track.
Dave, that sounds the most fun way to dilute. If you get to bottle 23 and it is only half full, do you say it is half full or half empty?-- Who cares 
Panoscape, I agree, dilution by weight is much easier and usually more accurate, but that is not the point of the post.
I will return tomorrow to see if anyone has worked out what I am on about, and give my explanation.
Reply:
Reading table 7, there is no need for correction for contraction due to the temperature of 60F. So, it is all equal. Now, to pay for an air conditioner to keep the proofing room always at 60F!
Reply:
Sorry Panoscape, that is wrong.
I don't use the TTB tables but from my understanding Table 7 is referring to expansion and contraction caused by temperature changes, not expansion and contraction that happens when adding water to alcohol at a constant temperature.
In my dilution above, the proof halved and the volume doubled. It looks as if I did a very rough rounding calculation, but it is accurate to at least 5 significant figures.
If we do another dilution it will show your deduction is incorrect.
1 gallon of 160 proof at 60F
plus 1 gallon of water at 60F
everything is at 60F but it gives 1.9608 gallons of 81.60 proof, not 2 gallons of 80 proof
Why does my original dilution give a nice round answer but not this one?
Reply:
The two compounds have different molecular sizes, and therefore the smaller ones fit in between the larger which causes the reduction in volume.
Reply:
I dilute each bottle individually with the timed pouring method I used as a bartender, then taste test every bottle I fill. If it seems a bit weak, I add some undiluted high proof spirit with an eyedropper. If it seems strong, I consider that a bonus for the consumer. Truly a handmade, craft produced liquor.
I can only fill 23 bottles a day before I fall asleep on the floor.
Reply:
I'll be your Huckleberry, Pete, but bear in mind I'm a liberal arts guy, and my chemistry schooling is limited to Mr. Ozuna's 11th grade Chem class. I'll assume your numbers are based in reality (and that you aren't just being a jackhole). So, based on our second example, you experienced about 2% contraction, and you say that in the first example where you started with half as much alcohol that you experience less than 0.01% contraction.
This is where I (almost certainly) step out of my depth. As I recall from Mr. Ozuna's class, water is a polar molecule so it clings to itself like a bunch of little magnets. On a hunch I checked and so is ethanol, but less so than water. Which leads me to my guess: as you add water to ethanol, water and ethanol molecules will pair up more densely than just ethanol molecules because water has a stronger polar attraction than ethanol, but at some point the molecules are all basically paired up and adding more water won't make much of a difference. My guess is that this point is right around a 1-to-1 ratio of water-to-ethanol molecules, which is why at 80 proof the change is negligible, but at 160 proof the change is significant.
Incidentally, and again this is a guess based on recollections of a class long ago, but I don't think the fact that the molecules are different sizes makes the difference, because unlike a jar full of marbles and sand, the molecules in a liquid are moving and bouncing around so there's actually a good deal of empty space (not as much as with a gas) but empty space nonetheless.
I like brain teasers, so I'm curious to hear your answer, Pete.
P.S. if I totally whiffed, it is on me, and if I got even close, it is to Mr. Ozuna's credit.
Reply:
Thanks Huckelberry/ Chris. Your explanation goes way beyond what I was expecting.I have no idea if you are correct with the science but it sounds good. First year University Chemistry was over 40 years ago, but I am starting to recall bits of the theory now you have prompted my brain.
I posted the blending example to point out that when blending alcohol and water there is not always a constant volume contraction.
I thought contraction always occurred but while testing a new blending calculator I found no contraction with a 1:1 blend at 80 proof.
It intrigued me especially as the proof was a nice round number.
I went on with a few more blend calculations and found that there are cases where there is a slight volume increase. ie 1+1= more than 2
eg 1 gallon of 55 proof at 60 F
plus 1 gallon of water at 60 F
gives 2.0034 gallons of 27.95 proof
It is only a very small expansion but it is definately not contraction.
I hope someone will do the 55 proof calculation with TTB tables and post the result here.
I have used the tables in the past but not regularly and I find them rather time consuming.
ps. ChrisNYC I suspect you are a bit more of a science geek than you are letting on 
Reply:
After starting this thread I got a bit more intrigued by this contraction / expansion wierdness so I did quite a few calculations and graphed the result. The graph makes it very clear that volume can expand when diluting.
It should now be fairly obvious what this post is all about
I wondered how ChrisNYC's Mr Ozuna could explain this expansion which is maximum around 50 proof diluted to 25 proof so I went back to basic parts.
When adding water to pure alcohol there is always contraction of volume
When adding water to already diluted alcohol there is sometimes expansion
Reply:
I found this (http://www.tsascience.com.au/images/pdf/LEC/LEC02_05.pdf). It describes the same relationship you are observing, namely that mixture contracts as water is added to pure ethanol, but that at some concentration it expands. The scale is different from your graph (mean molar mixing volume/mole fraction versus contraction/ABV), but it's derivations of the same relationship. One thing I do note, according to this graph, my guess of a 1-1 ratio being the turning point seems a bit shy of the turning point since the base of the parabola appears to be closer to a mole fraction of 0.6 (and not 0.5 as I predicted).
Evidently, Mr. Osuna (note corrected spelling) no longer teaches at my high school, so I still have no authoritative explanation as to why. If I find one, I will post it. If you do, please do the same.
