Ivo â€” Thanks. You've opened up a whole new field to me, and, I suspect, to others. Previously I had thought of apothecary jars only as those giant onion-shaped jars filled with coloured water in old pharmacy windows. Rambling around the internet, I discovered that they first appeared in Baghdad in the late Middle Ages, hence the Oriental appearance. Note the rudimentary string ring, originally for tying on the lid prior to sealing with wax.
Chloe â€” Bath salts was just a guess, hopefully reasonably well-informed, taking account of the midâ€“late 1920s date. The alternative is that they were purely ornamental, as Vesta Venetian
looks wonderful on a sunny windowsill with its fiery opalescence. My OH tells me that most wouldn't have bothered using a measure, just tipping in approximately the right quantity to soften the water.