Mercury(II) iodide (CAS 7774-29-0): storage and disposal
Bright red and easy to spot, mercury(II) iodide is a legacy salt in school, college and university stores, often kept for its striking colour change when warmed. It is classified as fatal if swallowed, in contact with skin or if inhaled, with organ damage from repeated exposure and very high toxicity to aquatic life. Keeping it dark, sealed and correctly described decides how a holder should handle it.
- CAS number
- 7774-29-0
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Acute toxicity
Serious health hazard
Hazardous to the environment
What to do this week
- Check the label is readable and write down the opened date if it is not already there.
- Check it is stored as toxic stock and apart from the items listed under "Do not store with".
- If you no longer need it, add it to your disposal list so it goes on the next collection.
Safe storage in a school or lab
Look at the colour through the glass without opening the jar. Red is the expected form. An ordinary warm shelf will not turn it yellow, because the change needs far more heat than any store reaches, so a yellow patch points to past heating or contamination and belongs in the record. Radiators, heated benches and sunny windows are still poor places for the jar. It belongs in a locked cabinet with a stock record, out of direct light, away from food and drink areas, acids and oxidisers. Old labels may say red mercuric iodide, and that is the same substance. The fine bright powder also marks anything it touches, so a jar on its own tray makes a leak easy to notice before it travels further.
How to tell it has deteriorated
Check the cap and label first, because the powder itself shows few signs of age. Legacy jars of this salt tend to have faded labels, brittle caps and red traces in the screw thread where powder has caught over the years. A red stain on a shelf or tray points to a failed seal. Yellow on its own is not a sign of decay, since the colour change on strong heating is a known property of the salt, although it does suggest the jar has a history. Caking or an unexpected colour that does not fit red or yellow is worth recording. So is a missing stock entry, which is common on stock of this age. None of these checks calls for opening the jar.
How it must be disposed of
By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a toxic laboratory pack with compatible chemicals.
A specialist collection takes it off site, and no other route applies. Keep it away from any sink or drain, out of general waste and skips, and do not attempt to treat it first. On the request, name it as mercury(II) iodide and add whatever the label says, because mercury, not iodine, is what sets the grouping. It is packed with compatible toxic solids and kept apart from acids and oxidisers in the lab pack. If an old reagent bottle containing the salt is also being cleared, list it as its own item with the name as written. The usual code is 16 05 06*. Mention any red dust outside the jar, since that affects how it is packed for the journey.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded inorganic chemical, not a laboratory pack | 16 05 07* |
| Hazardous waste | Yes |
The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.
Do not store with
- OxidiserToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- AcidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Named chemicals to keep apart
- Acetic acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Calcium hypochloriteToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Hydrochloric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Hydrogen peroxideToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Nitric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Potassium nitrateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Potassium permanganateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Sulfuric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Common quantities we collect
Usually held as: legacy stock.
Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.
Where it is commonly held
Hazard statements
- H300 Fatal if swallowed.
- H310 Fatal in contact with skin.
- H330 Fatal if inhaled.
- H373 May cause damage to organs through prolonged or repeated exposure.
- H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
- P260 Do not breathe dust, fume, gas, mist, vapours or spray.
- P262 Do not get in eyes, on skin, or on clothing.
- P264 Wash hands and exposed skin thoroughly after handling.
- P270 Do not eat, drink or smoke when using this product.
- P271 Use only outdoors or in a well-ventilated area.
- P273 Avoid release to the environment.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P284 In case of inadequate ventilation wear respiratory protection.
- P301+P316 IF SWALLOWED: Get emergency medical help immediately.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P316 Get emergency medical help immediately.
- P319 Get medical help if you feel unwell.
- P320 Specific treatment is urgent (see supplemental first aid instruction on this label).
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P330 Rinse mouth.
- P361+P364 Take off immediately all contaminated clothing. And wash it before reuse.
- P391 Collect spillage.
- P403+P233 Store in a well-ventilated place. Keep container tightly closed.
- P405 Store locked up.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
Substance as classified, dilutions may differ.
Questions
Could we show the colour change one last time before it goes?
No. The salt is classified as fatal if inhaled and in contact with skin, so do not open or warm it for a demonstration. Treat the jar as waste, keep it closed in the locked cabinet and arrange a specialist collection.
Our jar is yellow and not red. Has it gone off?
Not necessarily. The red form turns yellow on strong heating, and the yellow form can linger afterwards, so a yellow jar may have been used in an old demonstration or be contaminated. Record the colour and where it was found. It remains the same mercury waste either way, and it stays closed.
Should old ammonia test reagents containing mercury iodide go on the same list?
Yes, as a separate line with the label wording copied exactly. A reagent solution may be less hazardous than the pure solid, but it is not safe and it stays a mercury waste. State the bottle size and fill level, and leave the cap in place.