Month: February 2015

Iodine (I – Atomic Number 53) has very strong photography connections – and was used in some of the earlier photosensitive solutions as AgI – silver iodide – in daguerreotypes, named after Louis Daguerre.  More recently film emulsions have tended to be mostly AgCl and AgBr – Silver Chloride and Silver Bromide, but usually the Silver Bromide crystals have a small amount of Silver Iodide present to improve the light sensitivity characteristics.  Iodine is also found in seaweed, including Kelp – my first Iodine picture.

The discovery of Iodine related to seaweed too.  Bernard Courtois was using ash from seaweed as a source of Potassium for creating saltpeter (Potassium Nitrate) and one day noticed purple fumes when he added sulphuric acid to the ash.  The fumes condensed to form crystals and he guessed this was a new element – the name Iodine being given from the Greek ‘iodes’ meaning violet.  Iodine sublimes (goes right from a solid to vapour) at room temperature – so easy enough to sort of re-create this discovery.

Another use for Silver Iodide cystals is to seed clouds.  I’m pretty sure these clouds were not seeded though – I’m sure Amsterdam, much like Seattle – does not need any more clouds than they normally get!  As well as seeding clouds, Silver Iodide crystals are used in snow machines where a combination of high pressure air is used to reduce thelocal temperature – and then a jets of water and AgI crystals are sprayed together to give the ice crystals a head start.

Iodine Is very important to health and we need a daily intake of around 0.1 milligrams.  Most of the bodies 20 milligrams is found in the thyroid gland.  Radioactive Iodine (I 131) can accumulate in the thyroid – which can be used for good to fight cancer – but I the exposure is more sinister then normal Iodine can be taken (as Potassium Iodide) to replace the radioactive Iodine.  Potassium Iodide is also added to  table salt to help avoid Iodine deficiency.

The main source of Iodine is from the sea – not so much from seaweed these days – but from brine.

Next up is Cerium – Ce – Named for the asteroid Ceres!

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Aluminium (Al – Atomic Number 13). Or should I say Aluminum? Officially (IUPAC – The International Union of Pure and Applied Chemistry) say the former, and that’s the one I’m most used to – but in the United States Aluminum is the more common. IUPAC also accept this as a variant. The history of the name gets even more interesting, as it is this latter spelling that was first given by Humphry Davy in 1812 when he was working to isolate the metal from alumina (after he’d dismissed the name of Alumium).

Aluminium is the third most abundant element on earth, following Oxygen and Silicon – but is quite reactive so is rarely found as a native metal. The chief ore of Aluminium is bauxite – and I even remember from school geography that Australia and Brazil are the main producers – with cheap electricity being key to extraction. One thing I didn’t know – 5% of the electricity generated in the United States is consumed by Aluminium production!

Aluminium is light and resists corrosion (protected by a layer of Aluminium Oxide that forms when Oxygen from the air reacts with the surface or pure Aluminium, and these p[roperties make it perfect for use in the aerospace and other transportation industries – sometime on its own, but also as alloys which can increase its strength.  Another important use is for transmission of electivity – power lines benefit from the greater per weight conductivity compared to copper.  Aluminium foil and other forms of food packaging are more common uses of Aluminium – and an historically significant use was for the capstone for the Washington Monument.

Next up – Iodine!