Recording a batch in the inventory

Purpose

To make the shelf answerable from a sheet of paper: what is here, in what form, how much of it, how old, which group it stands in, and which pages of the course need it.

When to use it

Three moments. When a container arrives. When one is mixed — a stock or a working solution is as much a batch as a jar is. And when one is opened or finished, because two of the three dates on the line start at those moments rather than at purchase.

The chemical inventory is one sheet, one line per container. This procedure writes a line; the quarterly audit of the whole sheet against the shelf is the stock check.

Before you start

You should already have the safety data sheet on file, by recording a safety data sheet, because six of this line’s fields are copied from it. For a solution, you should have the true strength calculated by mixing to a final volume or mixing from a stock — the strength achieved, not the one intended.

On the bench: the chemical inventory; the container, already labelled; and its safety data sheet.

Procedure

1. Open the inventory and start a new line. A batch never overwrites the line of the batch it replaced: the old line is struck through and left where it is.
2. Copy the six identifying fields from the sheet — product name as printed, supplier, document version, revision date, date read, and where the file is.
3. Write the CAS number. It is the only field that survives a change of supplier, a change of spelling or a trade name.
4. Write the form: anhydrous, monohydrate, pentahydrate, or solution at a stated strength. For a solution, that strength is the one you calculated, not the one you aimed at.
5. Write the quantity on hand and the container and size, so that a formula can be checked against the shelf before a session rather than during one.
6. Write the three dates as three separate fields, because they are three different clocks: purchased or received, which starts the manufacturer’s own shelf life if the container states one; first opened, which is the real clock for a solid; and mixed, which is the clock for a solution and the one that runs fastest. Leave the ones that have not happened blank.
7. Write the storage group — acid, alkali, oxidiser, developing agent, silver, thiosulfate — and check on the shelf that the container is standing in it, against the incompatibility matrix.
8. Write the pages that use it: the parts and labs of this course that call for the substance. That is the column that pays, and it is the one people leave out.
9. On the day the container is first opened, go back and fill in the first opened date. It is a different day from the day it arrived and usually a different month.
10. When the container is finished, strike the line through and date the strike. Do not erase it: ten struck lines are a record of how fast you actually get through a substance, which is what tells you what to buy next time.

How you know it worked

• Every container on the shelf has exactly one live line, and every live line has a container.
• Any line can be read back to the sheet it came from and to the label on the bottle, and the three agree on the substance, the form and the CAS number.
• The three dates are three fields, not one, and the blanks are blank because those events have not happened.
• You can answer “do I have the tetrahydrate or the anhydrous salt?” from the sheet in thirty seconds without opening the cupboard.

If a step fails

Step 2, there is no sheet on file yet. Write the line anyway, with the sheet fields blank and the words sheet not yet obtained, and go to recording a safety data sheet the same day. A blank you can see is better than a line that looks complete.

Step 3, no CAS number appears on the container or the sheet. Record what identification you do have and mark the line identity not settled. Do not guess one from a name: the whole point of the field is that names move and it does not.

Step 4, two containers hold the same substance in different forms. Two lines. They are not interchangeable in any formula where the mass matters, and merging them is how a decahydrate gets weighed as though it were anhydrous.

Step 6, you do not know when it was opened. Write opened date unknown rather than a guess, and treat the substance as older than it looks at the next stock check. A guessed date is believed.

Step 8, you do not yet know which pages use it. Leave it and fill it in the first time a page calls for the substance. The column grows by use, which is what makes it accurate.

A batch was mixed and never entered. Enter it now, with the mixing date from the bottle’s own label and the strength from the label, and note in the line that it was entered late. If the label does not carry them either, the bottle is not a batch — it is an unidentified liquid, which this course treats as waste rather than as a puzzle.

What to record

The line itself, and nothing else: this procedure’s whole output is one row of the inventory sheet. The fields are, deliberately, the fields this course’s own chemical pages carry — identity, form, hazard data with its reference and the date it was verified, handling, storage, incompatibilities and waste — so that your inventory and the encyclopaedia are the same document at two scales, and you can audit ours if you keep yours properly.