Rochelle salt (CAS 6381-59-5): storage and disposal

On a school prep room shelf this tetrahydrate usually sits in a plain tub among the salts kept for crystal growing and carbohydrate tests. General stock rules apply: a dry, labelled, well organised store, with each tub dated on arrival. It is not classified as hazardous on the sources we checked, so it can share a cupboard with other general stock, but food grade supplies kept in the same room should be separated from laboratory stock. Keep the lid screwed down so that damp air and dust stay out, and write the full name on the label, since Rochelle salt is easily mistaken for other white sodium and tartrate salts on a crowded shelf. College and university stores often hold it alongside many similar crystalline reagents, so a clear label counts for more here than any special precaution.

A good tub holds loose, clear to white crystals. Damp air can clump them together or leave a wet film inside the container, and a tub that has spent years in a humid store may have set into a hard cake. This substance gives few distinctive signs of its own, so the general checks do most of the work: caking, clumping, a change in colour or smell, a faded label and no date of receipt. A solution kept in a bottle is a separate problem, since a cloudy or mouldy liquid shows it has stood far too long. Whatever the condition, it is described as it is found, and old or damp stock does not change the route.

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

Do not wash it down a sink or drain, put it in a general waste bin or skip, or try to treat it first, even though it is not classified as hazardous on the sources we checked. It stays a chemical waste and has to be described accurately. Waste code 16 05 09 is the entry held for it, and the paperwork is a waste transfer note, not a hazardous waste consignment note. Collection is by specialist route, with the tub packed in a lab pack with compatible stock. Record the full name, the tetrahydrate form, the quantity and whether it is a solid or a solution. Stock that has caked or gone damp is described as it is.

Usually held as: tetrahydrate.

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.