09:38 – I just shipped a core forensic science kit, which includes a bottle of Kastle-Meyer reagent. I add that bottle immediately before sealing the box, because we store KM reagent refrigerated to extend its shelf life. That bottle of KM reagent was the last one we had in stock, so it’s time to make up more.
I’m probably being more cautious than necessary. KM reagent is inherently unstable by design, but it’s actual pretty damned stable if stored under an inert atmosphere in a nearly full amber glass bottle with a granule or two of zinc metal to prevent oxidation, and an airtight cap. Unopened, that bottle should remain stable for years. So I’m debating making up a new batch of 30 or 60 bottles rather than the usual 15.
Not that it’s a big deal to make the stuff up in small batches. It just a matter of making up a 40% w/v solution of potassium hydroxide, dissolving enough phenolphthalein powder in the alkaline solution to make it 4% w/r to phenolphthalein, refluxing for half an hour or so over metallic zinc to reduce the phenolphthalein to phenolphthalin, and then making up the solution to double the initial volume with 70% ethanol.
11:34 – A man after my own heart.