The stock check, and retiring a chemical

Purpose

To walk the shelf with the inventory in hand and leave with three things: a corrected inventory, a list of what to reorder, and a decision on every container that is no longer what it says it is.

When to use it

Once a quarter, and at the start of any part of this course that introduces new chemistry — which is the moment the shelf is about to be relied on rather than merely stored.

It is not the procedure for entering a new container, which is recording a batch, and it is not the daily bench routine of opening and closing the laboratory.

Before you start

You should already know what destroys a chemical on a shelf and which of the five agents is at work on each of yours, from storage and incompatibilities. You should know why shelf life is far more a property of a solution than of a powder.

On the bench: the chemical inventory, printed or on a screen you can carry; a pen; the labelled waste containers for the streams you may fill; the notebook. Do this in daylight, with the cupboard open, and not at the end of a session.

Procedure

1. Take the inventory to the shelf. Work container by container, in the order they stand, so that nothing is skipped by being behind something else.
2. Is it labelled completely? Substance in full, form, strength, dates, hazard wording, initials, family. If not, it is waste — not as a punishment, but because you cannot state what it is, what it must not stand beside, or how to get rid of it.
3. Is it in the right group, in a tray, at the right height? Correct it now if it is not, against the incompatibility matrix.
4. Has it changed? Caked or damp where it should be free-flowing; browner than it was; cloudy, or with a deposit, or with a crust round the neck; a frosted bottle; a cap that no longer seals.
5. Is it past a date? Either one the manufacturer stated, or one your own notebook has set from experience. Read the three dates on the inventory line separately: received, first opened, mixed.
6. Will you use it before the next check? If not, write that in the margin. It is the cheapest information you will get today, because waste avoided at the point of purchase is the cheapest waste there is.
7. Apply the criterion. Use it only if you would be willing to record, in the notebook, that you used it and why you judged it sound. A chemical you would rather not write down is one you should not be using.
8. For each container you retire, write the retirement note before you empty anything: what it was, how old it was, what made you retire it, and what will replace it.
9. Route the material by its own stream — general chemical waste, or silver-bearing waste if it carries silver — into a container labelled by the labelling procedure. Read the disposal caveat before any of it leaves the house: the chemistry here is general, the law is local, it changes, and you must check your local regulations.
10. Strike the retired line in the inventory and date the strike. Correct every line whose quantity, date or group you found wrong.
11. Write the reorder list from the margins of step 6, and buy the quantity you will actually use.

How you know it worked

• Every container on the shelf was picked up, not just looked at along the row.
• The inventory now matches the shelf in substance, form, quantity and group.
• Every retirement has a note that says why, written before the container was emptied.
• Nothing unlabelled remains in the cupboard, and nothing retired remains on the shelf.
• There is a reorder list, and it is shorter than the shelf.

If a step fails

Step 2, a container is unlabelled or half-labelled. It is waste, and it is the most expensive waste there is, because it must be declared as unknown. Do not open it to sniff it, do not test it, and do not guess from the shape of the bottle. Route it as unknown by general chemical waste and read the disposal caveat first.

Step 4, a bottle has been topped up with fresh solution at some point. It now holds a mixture of two ages under a single date, and the date is believed. Retire it. This is the failure that hides itself, which is why it is retired on discovery rather than judged.

Step 5, there is no date at all. Treat it as older than it looks. Where the substance is a solution, retire it; where it is a sealed solid in good condition, date it found undated today and let the clock run from there.

Step 7, you cannot decide. That is the criterion answering you. If writing “used the sulfite that had been open two years, judged sound because it was still free-flowing” would embarrass you, the answer is retirement. The alternative — using it and wondering — poisons every result that follows and costs more than the replacement.

Step 9, you have no route for a retired container. Then it is stored, labelled, in its group, until you have one, and the stock check has produced a task rather than a disposal. Storing a known substance safely is always better than a disposal you cannot justify.

Step 11, the reorder list is longer than the shelf. You are buying ahead of your practice. Buy the quantity that reaches the next check, not the quantity that is cheapest per gram.

What to record

In the notebook, one retirement note per retired container: what it was, how old, what made you retire it, what replaced it. Ten of those are worth more than any published shelf life, because they measure your own storage conditions rather than somebody else’s. In the inventory: the struck lines with their dates, and every correction the walk produced. On a separate page: the reorder list, dated, so that the next check can see whether you bought what you said you would.