Many years ago while reading a C. S. forester book on the sailing adventures of Heratio Hornblower I came across an interesting word that I had to look up. It was a word meaning the air space remaining above the liquid in a barrel of the ships drinking water. I had a reason to use just such a word the other day to refer to the air space in a beer bottle. However, I couldn't dredge the word up from the depths of my memory. Does anyone know the word?
Hmmmmmm. Well, first of all, welcome PScoble!
Second, a couple of words are coming to mind. One of them is "ullage," which refers to the liquid lost in transit. I'm also thinking of "meniscus," that half-moon at the top of a body of liquid in a tube. Does either of those ring a bell?
"Headspace" is a modern term for that concept.
Meniscus is something else entirely. You'd have trouble seeing that in a wooden barrel, I expect.
Very good. The word "ullage" does ring a bell. That is the word I was looking for. Just last night I was discussing the point with friends (over a few beers) and the consensus was that is "wasted space".
...was that is “wasted space”.
Maybe it is time for a physics lesson; that "wasted space" is required.
Most liquids are incompressible although they change volume as temperature changes. If the bottle was completely full and its temperature increased, the bottle could no longer contain the pressure and would break, spilling the contents :-(.
The ullage or headspace is made up of gas which is compressible and allows the liquid to expand or contract as necessary without putting undue stress on the bottle.
HTH. BTW, thanks for "ullage".
Emmett