Back to the Royal Institution to their Family Fun Day yesterday morning, although even the youngest (13) of my family is now a little too old to find most of it ‘fun’. We mainly went to watch the lecture/demonstrations, the first involving low temperatures courtesy of liquid nitrogen and oxygen (the usual sort of stuff like shattering roses, unbouncyfying (or whatever the word should be) rubber balls, boiling a kettle of liquid nitrogen on a bed of ice, etc); the second involving non-Newtonian fluids (cornflour suspension in water, and slime made from PVA and borax).
There were several activities as well, but most of them were too young for my daughter (she did make some slime, although this turned into a somewhat brittle, only slightly rubbery precipitate, somewhat reminiscent of dried-up tofu, rather than slime). Then we looked at the exhibition of photos of Victorian microscopy, as well as a quick look round the museum exhibits, and then headed for the café.
It felt much busier – seemingly far more people – than the last fun day I went to. That one involved quite large explosions in the lecture theatre demonstration, which twice set off the fire alarm, each time the building being evacuated until the fire brigade arrived. Although this time they burned a biscuit soaked in liquid oxygen, it generated a very bright flame but not much smoke.
The slime reminded me that I need to find out where I can get some borax. My son wanted to make some slime about a year ago, I bought a bottle of PVA but then couldn’t find borax in any local shops. It used to be relatively readily available in hardware stores, sold as a cleaning agent, but it’s no longer available as such. I’ve discovered it’s now classified as a “Substance of Very High Concern” because of concerns about its developmental toxicity. It’s thought to impair fertility and may cause harm to the unborn child. ‘Borax substitute’ (Sodium Sesquicarbonate) is readily available for the cleaning side of things; unfortunately this wouldn’t work in the slime/silly putty manufacture, which involves cross-linking the PVA polymer.
A quick look suggests that you can still buy borax online either by the bucketful, or in overpriced little packets, but I shall try again locally first.