grams vs lugol iodine

[Tina]

Hi!
talking about iodine solution, I have recipies for gram's iodine and lugol iodine. Lugol is a lot more concentrated (4g iodine, 6 g potassium iodide and 100 ml distilled water). Grams iodine is 1g iodine, 2g potsassium iodide and 300 ml distilled water. I usually make up grams iodine. I dont dilute it but it still goes pale yellow after a few days.

When we do staining of onion cells to look at under the microscope, I often have complaints that the iodine is not strong enough. Should I be using lugols?

I am about to prepare iodine for the prac where you test for starch in leaves that have been in the sun or in the dark. I have had complaints about the iodine for that prac in the past. Which would you suggest? Or do you have any suggestions on how to make that work best?

Thanks
Tina

[Whspa]

My recipe refers to Lugol (Gram) Iodine and is 1g Iodine + 2g Potassium Iodide in 100mL water.

[noona]

Why not try a red onion then you don't have to stain it
it works a treat
Noona

[RosalieM]

I think I read somewhere recently that the Lugols is for staining, and the more diluted one is the one to use for starch testing. I now keep some of each. I figure if the Lugols doesn't get used I can just dilute it later for the other solution.

[lada]

We use red onion and it works well.
Re-iodine, Laboratory, page 125 says Gram's and Lugol and the same strenghts.( 1g iodine, 2-5g KI in 300ml water.
I keep iodine in dark bottles in a cupboard and seems to work for at least a few months, before losing its colour.
Hope this will help.
Lada

[Tina]

Hi
Thanks for your replies!
Why doesn't red onion need staining? Sounds like a good option to use.

One of the teachers wants iodine solution as dark brown as she uses as an antiseptic on her cattle. I guess I could just try adding more iodine to the potassium iodide solution. Does anyone see any problems with this?

Why does my diluted iodine (bright yellow) stored in brown dropper bottles in a cupboard, go so pale so quickly (within weeks?). Does it need to be stored in the fridge?

Thanks again
Tina

[RosalieM]

If you use red onions, the cells are already outlined by the red, so you just have to make sure the kids use a red layer, not a white layer.

Some sources say to keep iodine solutions in the fridge. I don't keep any of ours in the fridge and they seem to last for ages. Mine don't start out bright yellow though. Maybe using more iodine in the solution, like you suggested, will work.

[Ocker]

I never have a problem with Iodine fading, but maybe it's because I always disolve Iodine in ethanol first then add Pot. Iodide

[Tina]

Hi Graeme
Could I possibly have your exact recipie. I am keen to try something different.

Thanks:thumbup:
tina