On the specific gravity of liquids. No, seriously.
I have been scenting myself with Paul Smith for years now, ever since it has been on offer at 40% off in every London airport duty free shop.
Before that, it was Dolce and Gabbana for four years for the very same reason. By the way, it still is 40% off in the above shops, but I fancied a change.
Yes, I am cheap. So cheap that I always used to keep an almost-finished bottle of perfume to travel with. My lazy scientifically-untrained brain felt safe in the conviction that it would make all the difference between being allowed to check in and paying hundreds of pounds in excess luggage.
On the way to Dublin last October I bought a new 100ml bottle of Paul Smith EDT. A few specs of Dr B.'s Ph.D. in Chemistry must have rubbed off on me, because once I got home, I donned an imaginary white coat, weighed the new bottle (340g), compared it to an identical empty one (255g), and oh – only 85 grams difference, not really worth collecting empties for, right?
Hang on – what, I paid for 100ml and only got 85g? It's a liquid, like water, so surely it must weigh approximately one gram per ml?
Well, no. A quick search and I found out that liquids vary in density, which in turn means that they have different values of specific gravity, with pure water at 4 degrees C being the base line, with a value of 1.
So this is why 100ml of perfume can weigh as little as 85 grams.
And this is why on Friday I will dare flying to Copenhagen with an almost full bottle of perfume.
Let's just hope the plane does not tip over.