Those of you who have read ‘Uncle Tungsten’ by Oliver Sachs will know that once it was easy to get hold of almost any chemical that a budding young chemist might want to experiment with. When I was about aged ten I was the proud owner of a Lotts Chemistry Set and performed many an experiment in my bedroom or kitchen – adding acid to iron(II) sulfide, FeS, was one of the favourites. My dentist even gave me a test-tube full of mercury to play with! Now that the dangers of certain chemicals have been recognised, Health and Safety regulations sensibly dictate what can be purchased by members of the general public. It is definitely not a good idea to let young people play with mercury (although it doesn’t seem to have done me much harm!) or buy concentrated sulfuric acid etc.and chemistry sets containing any 'real' chemicals have disappeared from toy shops. However I recently discovered that even some relatively harmless chemicals can also now be difficult to get hold of although their sale is not banned or illegal. One such example is citric acid.

At this time of year many people make elderflower cordial. This is easy to make and a good recipe to use is:

1 litre water
1.5 kg sugar
1 sliced lemon
75 g citric acid
20 elderflower heads

Boil the water, add sugar and lemon, remove from heat while sugar dissolves, then reboil. Add citric acid and flower heads. Leave to cool, strain then bottle.

There is just one problem. You cannot easily buy citric acid anymore even though it is present in many citrus fruits such as lemons.

Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) is usually sold as its monohydrate (which can be converted to its anhydrous form if it is heated above 78 ^oC). It is a weak acid and acts as a preservative. All my local pharmacies no longer sell it to the general public as it is used by addicts to cut their heroin (it actually works as a buffer and increases the solubility of heroin in water). Luckily a shop in my local market which sells equipment and substances for home brewers does stock it. If you can convince them why you want to buy it then they produce a package from under the counter! Whilst talking to one of the pharmacists I also discovered that they do not sell the tried and tested old fashioned diarrhoea mixture ‘kaolin and morphine’ any more. Again this is due to addicts who allow it to stand to precipitate the kaolin then they concentrate the liquid to extract the very small amount of morphine present. The threat of terrorism has also put paid to the ready availability of certain chemicals. Try buying hydrogen peroxide in any strength after it was used by the shoe-bomber. Similarly getting rid of persistent weeds in the garden is now much harder. Sodium or potassium chlorate are very effective weed killers (the weeds mistake the chlorate ion for the nitrate ion) but because they are also used in home-made bombs they are now impossible to get hold of in any quantity. At this rate all that will be left for budding young chemists to experiment with will be simulations.