Storage rotation and shelf separation

Purpose

To put every container where its neighbours cannot hurt it and it cannot hurt them, and to arrange the shelf so that the container you reach for is the one that should be used next.

When to use it

Twice: when something new joins the shelf, immediately after it has been labelled and entered in the inventory; and every time a container goes back after use. This is the arrangement; the periodic audit of what is on it is the stock check, and the two are different jobs.

Before you start

You should already have read the six separation groups and the reaction behind each forbidden adjacency on storage and incompatibilities, and be able to state, for the container in your hand, which group it belongs to and what it must not stand beside.

On the shelf: trays deep enough to hold the whole of the largest single container standing in each; small bottles to decant into; a marker; and the inventory sheet.

!Sorting alphabetically is the mistake this procedure exists to undo

An alphabetical shelf puts acetic acid beside ammonia and sodium sulfite beside sodium thiosulfate, which is to say it arranges the shelf by a property that has nothing to do with what happens if two bottles fall together. Sorting by group makes the forbidden pairs impossible rather than merely discouraged, and it is the single change that prevents nearly everything the incompatibility matrix describes.

Procedure

1. Name the group before you name the shelf. Acids; alkalis and ammonia; oxidisers; reducing and developing agents; silver salts; thiosulfates. Write the group on the label if it is not already there.
2. Where a substance belongs to two groups it takes the stricter rule of both and it gets a shelf of its own. Silver nitrate is that case: it is an oxidiser and a corrosive at once, and it is the one that must never be near ammonia.
3. Put ammonia solution with the alkalis, and never on or beside the silver.
4. Put corrosives low, so that a breakage splashes at ankle height rather than at face height.
5. Leave the shelf above head height empty. Anything up there is retrieved blind, and gravity takes what you drop towards your face.
6. Stand every liquid in a tray, sized to the largest single container in it rather than to the total. Bottles do not all fail at once, and a tray deep enough for everything is one you cannot read the labels over.
7. Face the labels out, and put the oldest to the front — oldest by date first opened for a solid, by date mixed for a solution. Those are two different clocks and the second runs faster.
8. Decant a large stock into several small bottles on the day you mix it, and leave a small air space in each. Headspace decides how long a solution lasts, and a bottle drawn from repeatedly is refreshed with air every time it is opened.
9. Amber glass only where the solution is genuinely light-sensitive — silver nitrate, potassium iodide, nitric acid, ferricyanide. Amber for everything blurs the distinction and the bottles that need it stop looking special.
10. Wipe the neck and the threads before the cap goes back, and put the lid on immediately after use, including on an empty container. A crust of dried alkali is what cements a stopper shut.
11. Check where the shelf actually is, not where you think it is: away from food, out of a bedroom, out of an unheated shed or garage if the temperature can leave 5 to 30 °C, not in a cupboard that also holds bleach or drain cleaner, and out of reach of children and animals.
12. Update the inventory line if the container changed — a new bottle, a new size, a different shelf. A cupboard that closes makes this easy, because then the inventory is the contents of one enclosure rather than a memory of where things are.

How you know it worked

• You can state, for any container you pick up, its group and its forbidden neighbours, from the label alone.
• No acid stands within reach of a sulfite, a thiosulfate, a sulfide or a ferricyanide, and no ammonia stands within reach of the silver.
• Nothing is above head height and every corrosive is low.
• Every liquid is inside a tray that would hold the largest bottle standing in it.
• The bottle at the front of each group is the one you would want to use next.
• Every cap turns freely and every neck is clean.

If a step fails

Step 1, you cannot say which group it belongs to. Then you cannot shelve it. Read section 10 of its own safety data sheet — reactivity and incompatibility — and if that leaves it unclear, treat the container as unlabelled or undated rather than guessing a shelf.

Step 2, there is no spare shelf for the silver. A closed box on the lowest shelf, with nothing organic in it, is a shelf. Separation is about what can reach what, not about carpentry.

Step 6, no tray is large enough. Buy a smaller bottle rather than a bigger tray. Sizing the tray to the container and sizing the container to the tray are the same control approached from opposite ends.

Step 7, two bottles of the same stock have the same date. One of them has been topped up. Both dates are now averages of unknowns, and the label is worse than useless because it is believed. Retire the older by the stock check, which owns the retirement note, and never top up again. Where retiring means a waste decision, the disposal caveat is the page that governs it and this one issues no instruction.

Step 8, a decanted stock has crystallised in cold storage. Do not discard it. Solubility falls as temperature falls and the precipitate often contains the most important constituents of the solution, so it is warmed gently and redissolved — and then the shelf is moved somewhere that does not go below the band.

Step 10, the cap will not turn. It has cemented, which tells you the bottle has been breathing. Do not force it over a tray of anything; take it somewhere it can be worked on with the neck away from your face, and expect to retire what is inside.

Step 11, the only cupboard also holds a household bleach. Separate them or move one. A stop bath and a hypochlorite in the same enclosure is the chlorine pair, and it is the version of the incompatibility matrix that lives in ordinary houses.

What to record

The inventory line, which is the same one recording a batch writes: substance, grade, supplier, size, date received, date first opened. Add the shelf or group it now lives on, because that is the field that lets you check the arrangement without emptying the cupboard. Then record any move you had to make in a hurry — the bottle that had nowhere to go, the pair you found adjacent — since those are the shelf’s own defect list and they are what the next stock check should start from.