Phenolphthalein Agar

[Ian]

I use the dropper bottle trays as well. One with the dividers IN and filled to the top, and then one filled 2/3 and one filled 1/3 full (without dividers). I run a sharp knife or a spatula around the outside and they come out fine. Oh, I generally use double the amount of AGAR powder, so the cubes are quite strong and rubbery. (I guess that probably helps keep it all together!!)
Ian

[lada]

Thanks for the tip, Ian.
I find that in hot weather the cubes are sloppy. I will double amount of agar powder.
Lada

[Ocker]

After reading about that Gaur Gum I tried to substitute it for Agar due to cost of agar
Don't go there!

[rosaliemb]

I have used milk or juice cartons for moulds. Cut out the base to low height required, for 1,2or 3 cm blocks. Measure the height with a ruler allowing a bit more for shrinkage. Relatively easy to unmould , using knife blade around the sides or /and pull apart , cartons are flexible. Place cutting board on top of mould and upend, and it falls out or a little pressure on top releases the block. Blocks are small so if one "plays up' no worries . Don't re-use or use old ones as the wax finidh deteriorates and they don't unmould as cleanly.

One version of the prac requires cylynders of agar. I use the tube from a texta pen cut open at both ends, and gently pushed through a block of agar, then a pen with flat end of similar diameter to gently push it out of the tube. A few failures but patience gets enough formed.

I have also used a wire cheese slicer to cut the agar, as well as a knife.

I'm going to put more agar in my mix too.

My thanks to all contributers
Rosalie (another one)

[bindibadgi]

Thanks from me also - awesome idea to use the dropper trays!

I made a batch on Friday with tray dividers in, & this morning I turned one upside down, pulled the sides apart a little & out came 10 perfect pink cubes!

Chemtalk absolutely rocks!!

[estelle]

Great excuse to ask for chocolates!
And lots of them.
I have a perspex ferrero rocher chocolate container that is about 21 cm square, the base is 2cm deep and the top 1cm. Makes an excellent setting dish for the agar. I have figures out the amounts to make so it works out perfectly. Then I just run a knife around the edge and drop it over a laminated sheet of graph paper.It might have been a special edition but worth keeping an eye out for in the shops.

I find the other ferrero perspex containers that have, I think they come with 16 chocolates are just the right size to store 8 dropper bottles in and for sending them out to class, the top isn't so good because the bottles tend to fall over but the base is just right.
So now you have a legitimate reason to ask for chocolates

[Xenon]

Hi Tina, just noticed your post. Yeah, what Ian said. I run a metal-blade spatula down the sides and tap it out onto a flat surface; can only guarantee if using my recipe, though.

[Ian]

Hey! The dropper dropper bottles work fine, but I'm going with Estelle! What a great excuse for chocolates!!!! Wee Hee!

Ian

[Labbie]

Yes I agree go the chocolates> Well done

[vlclabbie]

Hey all, is there any use for phenolphthalein agar after it's discoloured....? The Y11 biol class didn't use it all & I have a bit left.... Any thoughts... besides smearing over my arch nemesis teachers (see the Teacher Declaration thread for clarity!) car!!!

Kel

PS I wouldn't really.... promise!!!!!

[Ian]

Hey all, is there any use for phenolphthalein agar after it's discoloured....? The Y11 biol class didn't use it all & I have a bit left.... Any thoughts... besides smearing over my arch nemesis teachers (see the Teacher Declaration thread for clarity!) car!!!

Kel

PS I wouldn't really.... promise!!!!!

Well, You could feed it to your "Arch nemesis teacher" with a scoop of ice cream and a dollop of cream....
Now, wouldn't that give him the s**ts!

Then.... maybe not!

Ian

[lada]

Ha, ha

We just finished the same prac and thanks to Ian I made up perfect little cubes. Using double agar made them nice and firm. Teacher and students suitably impressed. I love this site.
Lada

[vlclabbie]

ooooooh love the jelly approach Ian!

Spose I shall just turf them out.... seems a waste!

Thanks,
Kel

[estelle]

Does anyone know if the phenolphthalein agar will still work if you have to reheat it?
I made a tray of it yesterday to be ready for a prac period 4 and the cleaner left me a note to say she came in, in the dark and threw her bunch of keys on the bench not knowing I had some dishes setting. Said she is sorry if she ruined it. @@##$
Couldn't really send it out to biology class with a 25cm freakin crater in it.
sS I reheated it but it has gone a rather dark browny pink colour.So not sure if it will still react.???
I am thinking I should probably waste some more time and make another lot up.
Estelle

[dime]

I think it will probably still react. For years I made it and it would turn dark brown on cooling. But it still worked when put in the acid. It just wasn't as pretty.

[Tina]

Hi Estelle
After my previous failures trying something similar I would try a new batch. but then you cont have much time for a new batch either. But then again, you might have more luck than me. Actually, you are probably doing that prac right now. Did it work?
cheers
Tina

[noona]

Hi All
I just made some yesterday in Ice cream containers they very well thatns for the tip
Have a grat break and I hope the Easter Bunny comes to ALL

[estelle]

Hi all,
Yes it still worked after reheating the mix.
I ended up having enough for probably 5 classes. The bio teacher forgot to tell me he only needed enough for 4 groups and then he ended up having bio students away on an excursion and having to "babysit" year 10 in the same class so didn't even get to use 4 lots.
He wants to run it again next term. I am contemplating wrapping the left over up in glad wrap, putting it in the fridge and testing it next term with H2SO4, if it still works he gets it again!!
Estelle

[rae]

Hi Estelle,

I had mine for at least 3 weeks in the fridge after we had used it and the colour was stll fantastic and the gel was even better than when it was fresh so I think it would be fine to keep in the fridge over the holidays. Its only 2 weeks afterall.

Lorrae

[merilyn]

Hi all

I'm a real newbie at this - only been a labbie for a couple of months, so would appreciate some help.

I was asked to prepare some phenolphthalein agar. I used the "recipe" from "The Laboratory" by B. Dungey, which said to use 18g agar, 4g sodium hydroxide and 1 litre of distilled water, and to add the phenolp. until the agar turned a deep pink. Not being sure what "deep pink" is, I added the phenolp. until it didn't seem to be making any difference to the colour. It was pink, but probably not what it should have been. After leaving it to set, the colour appeared much paler than before. The instructions said to leave it a few days as the colour would develop better. but time restraints did not allow for this - it was made less than 24 hours before using. The result was that the students found it difficult to notice any colour change when added to acid.

One of the teachers suggested that the phenolphthalein may have been old, or diluted. Any other suggestions?

Where is it best to store it? Should it be in the fridge?