h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This note surprises me because I thought one of the definitions of liquids and solids is that they are incompressible. Is there a different meaning of compress that a chemist would use that a physicist would not?

You are correct, liquids are pretty incompressible. What happens when you mix alcohol and water is similar to pouring a bucket of sand into a bucket of tennis balls. The alcohol particles fit in the spaces between the water molecules. Water cannot be compressed though it has these spaces because each particle is repelled from the other if they get too close.

I think that the author is using 'compress' in a non-technical way in this article.

Rather than referring to the ability for the liquid to be squashed up into a smaller volume it is being used to refer to the fact that if water and alcohol are mixed in the proportions that Mendeleev worked out that their weight is at a minimum.

If alcohol and water are mixed then the weight of the mixture is less than the weight of the original separate fluids. What Mendeleev worked out is what proportions of alcohol to water give the biggest ratio between the weight of the mixed alcohol and water and the weights of alcohol and water started with. That last sentence is a bit confusing, I think that this might explain better:

weight of mixture(alcohol & water) : weight of alcohol + weight of water
where ':' means 'the ratio between'
is greatest at Mendeleev's proportions

but I could be wrong (about it being less confusing).

-Koshmar

Because my mind thinks of these words scientifically, it's alarming to read about destruction of weight without an accompanying mushroom cloud.

If you are getting x proof vodka, then the mix of ethanol and water is known. Since you know the proof, then the mass and volume are directly and linearly proportional.

Is the glass for the bottle for selling the vodka excessively valuable? Perhaps the density of the fluid is 'changing' because of 'bad business practice'? Perhaps there is no good way to find out the proof of this solution, so Mendeleev did some rough empirical solubility tests without Avogadro's number?

I still don't get it.

To be honest you've confused me now. My original version of my answer was that the volume is lower which I think is right. The weight *must* be the same between the unmixed and the mixed solutions. But the volume is different therefore the density has increased.

My mistake.

As a footnote it's interesting that Mendeleev's paper (if the title is quoted right) doesn't appear to be online anywhere. Which is wierd.

-Koshmar

If your mix is 40 % alcohol 60% water, it's density may be higher than one might suppose from averaging the molecules. This seems irrelevant to commercial transactions. If you have a dl or a ml or a l of this solution, the alcohol to water percentage doesn't change and the density doesn't change. The only thing that changes is the size of the container.

Therefore, I don't understand why you might like to sell vodka by weight, unless:

You have no other way of determining the ratio of alcohol to water, or

The cost of glass is so high that you don't care what ratio your customer might want, you only sell it at maximum density, or

Vendors of alcohol are so disreputable that you need them to weigh the measured volume of the solution as they sell it to you, so you can tell at a glance if the vodka has been diluted for profit-taking purposes, i.e., 'there's a trout in the milk'.

This type of conversation is from "you can't sort it out without vodka" category

Na zdrowie!