Monday, 20 June 2016

10:15 – Barbara is off to the gym and running errands. This afternoon and the rest of this week we’ll be filling and labeling bottles and making up science kit subassemblies.

One of the problematic chemicals has always been starch indicator, which is a suspension of “soluble” starch in water. We use a 10% m/v solution of thymol in IPA as a preservative. That generally works pretty well, but we sometimes get mold or fungal growth in some of the bottles. We just threw out a bunch of them the other day that had assumed a dark brownish gray cast. They’d still serve their intended purpose, detecting very small amounts of iodine, but their ugliness offended me. So yesterday we tried something different. I made up a small batch of the starch indicator, enough to fill 60 bottles. After they were filled and capped, we put them in a pot of boiling water and let them boil for ten minutes or so. That’s enough to kill any microorganisms present, although not spores.

The bottles are polyethylene, which softens but does not melt at the temperature of boiling water. I was a bit concerned that boiling would deform the bottles severely, so we ran a test recently with just one bottle in a pan of boiling water. It swelled a bit, but did not melt or deform.

Killing spores would require heating the bottles to 121C (250F) in a pressure cooker or autoclave. Unfortunately, it would also melt the bottles. So if just boiling them doesn’t keep them from growing mold/fungus, we’ll have to use a 19th century technology which is still occasionally used today for special purposes. It’s called Tyndallization, and was widely used for preserving food before pressure cookers became widely available.