It's been a while since we actually did an honest to goodness science experiment. I set out to fix that today by suggesting a realy simple one that will also go towards one of Catherine's Girl Guides badges - Invisible Ink.
I googled invisible ink and found quite a few different ideas. While it was the old lemon juice one I needed I also found ones involving baking soda and corn starch so I think we may have to explore this a little more over the course of the week.
About.com had a good page on the matter so Catherine read it and gathered what we needed. Then she and Harry got down to business with paintbrushes and lemon juice.
After the juice had dried I lit a candle and we applied heat to the pictures. The lemon juice turned brown as expected. Lesson learned. But of course then we saw the swirls of soot on the underside of the paper. Harry stuck his finger on one dark patch and found it was just a thin and fragile layer of soot. Catherine wanted to try more soot pictures so we held paper above the candle and moved it around to get interesting patterns. As we did so we watched the way the smoke from the flame rolled up and off the paper.
I think that's a good thing to remember with kitchen experiments sometimes. What you may set out to do may be neat but given some fun materials the kids will explore and experiment and reach farther.
There's another way to make lemon juice ink appear with salt and crayons and I think we'll try that tommorrow. I'll also take down the litmus paper and strew a few more interesting things on the kitchen table and see where the kids take it.