Saturday, 19 April 2014

PH imbalance


A bluebell wood just outside South Wraxall yesterday. It's the long-distance haze which I like so much.

I have been thinking a lot recently about how much of my life is involved with the battle between acid and alkali. I was about to say that it is usually a silent battle, but then I was reminded about the slightly stressful opening of the hand-grenade in my search for one form of nitric acid inside it.

I was brought up in an acid area, but now I live in a very alkali one and I am not sure it really suits my nature.

The ancient heaths of Surrey nurture heather, gorse and silver birch, and adders slither out from their shade to warm themselves up into action. The fine sands around Frensham Ponds are pure white and possibly too acidic to be quarried for architectural purposes, even if you were allowed to.

Here in Bath, one is literally surrounded by alkali, and acid - in the form of coal smoke and car fumes - is its mortal enemy. I don't really understand the situation scientifically, so I generally treat the the whole thing as a classic battle of good against evil, which adequately suits my purposes.

Neutralising the enemy always means redressing the PH balance, and the forces of alkali have to be deployed in vast amounts to outnumber acid's little pockets of resistance.

The strange thing about concentrated alkalis and acids is that they both burn, and I have the scars to prove it. The burn from wet quicklime is every bit as bad as one you would get from a 50% solution of sulphuric acid, and hurts just as much.

If I use a non-ionic detergent to clean the grease stains from a piece of marble, I am reliably informed that the product is in absolute perfect balance between acidity and alkalinity - it is politically neutral, like the United Nations forces are supposed to be. It just goes in, does the job, then goes out again without having done any harm.

I have made two near-catastrophic mistakes with both acid and alkali - one was made when I took the lid off the top of a bottle of industrial-strength acid and decided to sniff the fumes which were steaming from the neck of the container. The other was made literally a stone's throw from where I am writing this, when I was cleaning the carvings on the side of Bath's Guildhall many years ago.

Part of one process to neutralise the acidic build-up against oolitic limestone is to give it a hot lime poultice. It goes as follows:

You take an ordinary metal dustbin up onto the scaffold and fill it about one third with water. You then pour in an equal quantity of chipped quick-lime and quickly put the lid on it. Then you stand well clear.

Within seconds, the dustbin begins to shake and rattle as steam begins to rise from the edges of the lid. Seconds after that, the water actually boils as if there were a fierce flame beneath the dustbin, and the lid rattles around as if there are fifty large rats trying to escape.

The Romans described this reaction as all the heat absorbed by the firing of the chalk to make lime, being released in the form of a battle between fire and its mortal enemy - water - the two being unable to peacefully coexist side by side. This may sound like a superstitious way of viewing it, but it is just as relevant as any other, more scientifically modern explanation. It all boils up to the same thing eventually.

After a few minutes the boiling subsides, and when it is all gone quiet you lift the lid to find that the dustbin is full almost to the top with a thick, very hot, white cream. You then take it out by the trowel-full and slap it against the stonework to a couple of inches thick, as if you were plastering the inside of a 1960s Italian restaurant. You cover the results with plastic, then leave it for a few days for the alkali to work its magic.

It was getting dark and I was on my own on the scaffold, but I needed to complete the job before leaving, so I was in a bit of a hurry as I threw the hot lime against the stone figures.

I slapped the last, heaped trowel full of boiling-hot lime against a hollow pocket of stone, and a lump of about two inches in diameter came flying back at me, straight into my open eye, completely covering it.

I cannot tell you how painful this is, other than saying that hot lime burns in two ways - through the actual heat, and also through the concentrated alkali. I had about two seconds to save my sight in that eye.

I remembered that there was a hose-pipe at the far end of the scaffold, and I blindly ran toward it. Fumbling for the tap, I turned on the water and held the end of it against my eyeball for about two minutes. I was completely soaked of course, but I was relieved to find that I could still see out of my reddened and stinging eye. The skin over my cornea grew back in a few days.

Yes, I know, I should have worn goggles, but like I said, it was getting dark. All in all, I have been a lucky geezer when it comes to industrial accidents - so far.

16 comments:

  1. Pretty picture!

    But holy crap - do you have a death wish or something?

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    1. No, it's all part of my job and life.

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  2. The suspense was almost too much for me as you ran blindly for the hose pipe. And then as you fumbled for the tap and got the hose pipe to your eye, the relief. Don't do this to me, I can't stand the strain. The rest of the post could have been a load of bollockss for all I know. The picture at the top made me do a double take because it is exactly the same view as at the top of my garden; I thought for a terrible moment you were here.

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    1. Hitchcock couldn't have described it better

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    2. Yes, that terrible moment when I thought he was outside in the garden.

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    3. That has to be the funniest comment of the week, Phillips.

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  3. Holy Saturday! You were one lucky son of a gun...what suspense!

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    1. I didn't tell you about the mix to make nitro-glycerine when I was a kid. I stopped myself. That's intelligence.

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  4. Work place accidents are too easy to come by, especially at the late and tired end of the day. I'll spare you mine, and I sympathize with yours.
    By the way, I once smelled sulphuric acid. The bottle looked so attractive in chemistry class I pulled the lovely glass stopper and inhaled. I replaced the bottle, with stopper, barely.

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  5. My good friend 'Saint Theresa of the Floral Tribute' once asked me to make 'slaked lime' for her, for some process to do with her flower arrangements. It involved heating the lime, then adding water...... not to be encouraged.

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    1. To be a bit pedantic, Cro - sorry - you don't need to heat the lime before slaking, it heats itself just so long as it is quick lime - i.e. unslaked. I cannot imagine how it's used in flower arranging!

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    2. I just followed a recipe. I think she used it for dipping certain leaves, that then become skeletal.

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    3. There's a spring near here which calcifies anything left in it for a few days. instant sculpture.

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  6. Tom, having read this, I now know why I dropped chemistry from the school curriculum at a very early age!

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    1. Ah, but they would have forced you to wear those protective goggles, Weave.

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