Archive for July, 2010

Water is blue!

July 7, 2010
Composite picture showing a white box being being filled with water.

Composite picture showing a white box being being filled with water. The left hand side shows the box empty, the middle shows the box with approximately 5 cm dept of water, and the right hand side shows the box with approximately 10 cm depth of water.

I love my colleagues at NPL.

First of all James Miall sent me a link to some measurements of the transmission spectrum of water H2O and heavy water D20. The measurements are relatively simple and the paper is well written and straightforward.

Then Jenny Wilkinson took me to one side and very patiently explained to me how to clearly see the blueness of water. She filled a white polystyrene box with water – and viewed against the white of the box the water was clearly blue. I have tried the experiment at home and took photographs of a polystyrene box empty, with 5 cm of water , and with 10 cm of water. I have combined the three pictures into a single composite picture (above). Even allowing for the vagaries of colour reproduction in cameras and screen monitors, the water appears to be blue! At least it does around the edges.

So now I am trying to understand why water looks bluer when viewed against the sides of the box, but appears essentially clear when viewed against the base of the box. I think that it is because the materials of the wall appears less bright but when I try to get quantitative, it doesn’t make sense.

I think I will just leave the picture here and hope that another of my colleagues can explain the observation.

Is Air Conditioning Necessary?

July 4, 2010
Air Conditioning

Air Conditioning

We have had a few warm days in London in the last couple of weeks. And it makes going into my air conditioned laboratory a real pleasure – cool air with just the right humidity to make it feel comfortable. Ahhhh. It feels great. And I would really like to ignore how much it costs to create. However NPL as a whole is intimately aware of how much it costs – they (and that means you!) have to pay the electricity bill! So I do feel a little guilty as I enjoy the coolth.

And with the sheer pleasure of working in an air conditioned office in mind, I would like to draw your attention to an article in the LA Times suggesting that the US might want to ‘turn down’ its air conditioning for a variety of reasons. Two particular arguments struck me forcefully. The first was the carbon emissions: in the US it is equivalent to every household buying an additional vehicle and driving it for 7000 miles per year. More interestingly the article comments on how air conditioning has eliminated a raft of much lower technology approaches to the problem of keeping cool in warm weather. These involve drinking cold drinks, doing less, the creation of shady spaces – and then the simple fact of sitting in the shade! The article also links the avoidance of the outdoors in warm weather to American obesity and exercise issues. And perhaps more radically it hints that human habitation of the southern states of the US such as Arizona is so critically dependent on air conditioning that – in a hot and unforgiving future – humans may need to retreat from such hot frontiers. It’s just a hint, but it is a curious insight into what we may yet have in store in the UK.

Enjoy the warm weather 🙂

The colour of heavy water

July 4, 2010
NPL Heavy Water Sample

NPL Heavy Water Sample

I love working at NPL! Over lunch the other day I spoke with my colleague Richard Rusby about my doubts over the explanation I had read about the colour of the sea. This explanation stated that the sea is blue because water is ‘blue’. And the justification for this assertion was that molecular vibrations of the hydrogen in the H2O absorbed red light – a verifiable fact. However the colloquial justification of a nameless colleague was that if a vial of water was compared with a vial of ‘heavy water’ the ordinary water looked noticeable blue. Richard said that whenever I wanted I should ‘pop down’ and he would show me a vial of heavy water. Wow! It transpired that Richard had had a vial of heavy water around for many years without quite knowing what to do with it!

The Comparison and the Amazing Discovery

The comparison was disappointing because there is no noticeable difference in the colour of vials of heavy water and regular water. Normal water does not appear even slightly ‘blue’ when held against regular water. Clearly there is more to investigate here.

However the sample of heavy water was amazing!

Label showing heavy water sample was obtained in 1935!!

Label showing heavy water sample was obtained in 1935!!

First of all, it was stored in a solid wood block with a type written label stating it was made in 1935! Opening it up (see top picture) it was clear that it had been made at the Norsk Hydro plant in Norway.  According the ever reliable Wikipedia this plant only began production in 1935. This was the same plant that was  the object of a daring commando  raid in the second world war to prevent the Nazi from creating a nuclear bomb. And I held in my hand a sample from the first year of production of that factory.

I felt shaky all afternoon. I had held a piece of history in my hands – an object that not so long ago people would have given their lives to possess. I still don’t know how to proceed about the colour of the sea issue, but I feel – astounded to have encountered a vial of heavy water of such esteemed pedigree. And it had been in a cupboard in my own department all these years! I love working at NPL.

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