Inspired by my brothers and thinking ‘how hard can it be?’ I decided to add car windscreen wash to a growing list of ‘home produce’. OK so I did not make the IPA, nor the surfactant, it’s still home-mixed though.

The screen wash I bought recently says it contains methanol/isoproanol, <1% non-ionic surfactant, sequestrant, parfum. This is a fairly simple shoppiong list; dentaured alcohol, a surfactant (reduce surface tension ie less smearing), a sequestrant (chelating agent presumably helps bonding onto and removing dirt?) and something smelly. Scratch the last 2.

Following a little guidance I mixed up 200ml IMS with 800ml tap water and added a tiddly dab of Decon Neutracon that happened to be lying about at work (less than 5ml, but no I shouldn’t have liberated it, mind you it has been sat there for 6 years without being used which puts the stuff beyond its shelflife, so maybe I am providing a useful testing service). It’s a pH neutral mix of anionic and ionic, but to be honest I am not that fussed, a dab of washing up liquid would probably achieve the same.

The resultant mixture is sat outside my back door at the moment with a remote temp/RH datalogger (no, that was not liberated from work). I reckon it shouldn’t freeze until – 10°C, which should be fine even in the present more-chilly-than-usual-weather . Results to follow along I hope…

Denatured alcohol is 10% methanol, 90% ethanol (pretty much).

This works out to a molar weight of 44.667 g/mol

so 200ml contains 4.48 moles

molality of the solution is: (4.48 mol alcohol / 0.8 kg) = 5.59 molal

5.59 × -1.86 (freezing point depression of water) = -10.4°C

Educational and useful, although potentially paint prejudicial.