Iodine – I – With Silver makes photos, rain and snow

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.

Kelp
Kelp

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.

Clouds over Amsterdam
Clouds over Amsterdam

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!

More kelp
More kelp

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