I found this activity in an old report from CHEM ED 95 and I was struck by how old this experiment was. This experiment was done by Glauber about 1650.
Dissolve 190 g of sodium silicate (water glass) in 190 cm3 of distilled water. On the bottom of a two-litre beaker, place well-spaced crystals of nickel chloride, cobalt chloride, manganese(II) sulphate, copper sulphate and iron(II) sulphate.1 Carefully add the water glass solution to the beaker containing the crystals. The films of these insoluble silicates form semipermeable membranes.
Serendipitously, a neat little video2 showing crystals growing in sodium silicate solution was recently tweeted by William Barron de Burgh, a teacher at Dame Elizabeth Cadbury School, Birmingham, UK. The video captures the iron(III) chloride added to water glass in real time. I highly recommend this video and activity. William also posted a couple of photos of his crystal garden.
- Unfamiliar with this old favourite? Try B.Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 3, 1990, page: 379
- Video of crystal garden posted by
Read individual Tweet on Twitter[JLH]