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1. CHEMICAL SAFETY2


2  Taken from BDH Chemical Hazards Data Book. Pub. BDH, England 1984. Also from the computer based version of the same book. Published by BDH Software.


1.1 Chemicals involved and risks assigned

Agar (as powder and gel - non ammonical) : No risk. May cause sneezing if inhaled when in powder. As the gel, it may cause slight indigestion if swallowed in quantity.

Ammonia, 0.880 S.G.. : Corrosive. Harmful to skin and eyes. Irritant to respiratory system. If spilt on skin or clothes, it should be washed off with copious amounts of running water. If in eye, the eye should be irrigated with water for at least 15 minutes before medical attention aquired. This liquid should only be used under an approved fume hood / cupboard. Gloves and eye protection must be worn at all times.

Ammonical agar gel : Do not eat. If swallowed, give plenty of water and seek medical attention. The gel will undoubtedly smell - it should be kept in a well ventilated area.

Iodine (solid) : Corrosive - may cause blisters with prolonged skin contact. The vapours given off are irritating to the eyes and respiratory system, so should only be used in a well ventilated area. If swallowed, give plenty to drink and seek medical attention. If solid comes into contact with the eye, the eye should be flushed with running water for 15 minutes before seeking medical attention. Gloves and eye protection must be worn when handling this solid.

Nitrogen triiodide (NI3.NH3 and NI3.3NH3 - mixed adduct) : This solid is a black crystalline aggregate which is extremely unstable when dry. It has also been known to explode under water!. The solid is made by the reaction of .880 S.G. ammonia with iodine and is stable when kept under the ammonia. ALL SAFETY PRECAUTIONS FOR AMMONIA SHOULD BE OBSERVED FOR NI3 WHEN STILL UNDER AMMONIA. The solid will cause damage to the skin if touched and will undoubtedly blind if it comes into contact with the eye and detonates. A face shield must be used when handling.

Sodium thiosulphate, 10 to 15% solution : May cause irritation if swallowed or in long term contact with the skin. All spillages can be mopped up with water and run to waste down a sink. Any contact with the eye should be treated with running water for ten minutes followed by seeking medical advice.

Chromic acid : A solution containing potassium dichromate and concentrated sulphuric acid - this solution is a highly powerful oxidising agent. Gloves and eye protection MUST be worn at all times when handling. If any should come into contact with the eye, it should be drenched with water for fifteen minutes and medical attention sought IMMEDIATELY. Chromic acid causes deep burns. All spillages should be neutralised with sodium carbonate then mopped up with copious amounts of water.

1.2 Nitrogen triiodide (predominant form)

Nitrogen triiodide is a very difficult substance to handle being shock sensitive when dry (it may be detonated by vibrations from a fume cupboard or when stroked by a feather even) - it also forms large crystal aggregates when made. This crystal size should be avoidable by using a finely ground iodine and then sandwiched between two filter papers and immersed in .880 S.G. ammonia. This should prevent aggregation.

The smaller aggregate will have one major side problem. With the smaller iodine granule size, a larger surface area will be formed overall. The larger the surface area, the higher the explosive potential and the lower the energy required for a large explosion (due to shock waves from neighbouring granules).

All residues and equipment can have the NI3 destroyed by washing with a 10% sodium thiosulphate solution and left until all the black iodide has become colourless. The resulting solution can be washed down the sink with large quantities of water.

1.3 Explosion risks

Nitrogen triiodide (either the mono-ammonical or tri-ammonical species) requires only a matter of a couple of joules of energy to explode, resulting in iodine vapour and nitrogen gas being given off. However, smaller crystals of NI3 are produced on the explosion. These are dry and will also explode on contact.

All areas where the either the exploded or dried triiodide has been prepared must be kept clean at all times with possibly a benchcoat on the surface.

In the event of an explosion, remaining crystals of the nitrogen triiodide can be neutralised by washing the area with a 10 to 15% sodium thiosulphate solution. This solution is left for ten minutes and washed down a sink with plenty of running water.