Phenolphthalein Agar

[Loopy]

Hi Merilyn! Welcome!
I use 1g of phenolthalein powder for my phenolthalein agar and have never had any problems with colour.
Hope this might help you...

[lada]

I have used a very small amount of powdered phenolphthalein. It works really well and does not dilute the agar mix.
Good luck
Lada

[Lab]

Thanks everyone for their answers and suggestions. Every year I make this and until this year when I was told to use gelatine to set it with the agar it as been a dismal failure. So I look forward to trying the receipe next year. Love this site.

[Ocker]

Yeah! I tried jelly once because of the cost of Agar, as you state "dismal" then I tried Guar gum, that was worse, it might cost a bomb but there is no substitute

[merilyn]

Thanks, everyone, for your tips and advice. I just hope I remember all this for next time! Being new, I feel pretty bad when things don't go to plan. Next time I'm not sure of something I'll be checking here first.

[estelle]

Just letting you know that I kept the leftover phenolthalein agar in the fridge over the holidays wrapped well in gladwrap and we used it in the biology class yesterday with success.
I tried it before sending it out to class just in case, but the reaction in the sulfuric worked just fine.
Saved me wasting it and saved me having to make more.
Estelle

[vlclabbie]

Cool Estelle! Will remember that - I put mine in the fridge in their containers but they must have some air leaks..... will wrap em up next time!

[rae]

Hi Just revisiting an old topic with a new question.

We always have heaps of gel left over. Has anyone tried keeping the gel for any length of time? I was thinking of giving it a go!!

[Ian]

I use the dropper bottle trays with the dividers still in. I run a knife blade around the edge before I tip the cubes out, as I would with a jelly mould . I get ready made cubes that can be left as 3cm cubes or cut down in halves or thirds, etc

regards
Ian

[RosalieM]

I have kept the normal agar in the fridge in flasks with parafilm sealing it for quite some time. I think if you kept the phenolphthalein one it would be ok but keep in as air tight as possible and not ready made in the trays. I did try that once and it just dried out too quickly.

[SGG]

Been making this agar for 4 yrs and had the worst time this year! Used Agar 750 gel for first time and the first batch didn't set. The company suggested doulbling the amount - this set so hard the top cracked! Tried for the middle amount and finally third time lucky. But.....half a 500g container gone !
Regards
Sue G

[merilyn]

Back on Page one of this topic is a recipe posted by Xenon. I tried it this year (after a disastrous first attempt last year) and it worked perfectly. I was sooo happy, pity there was no one here to share my jubilation with!

[Narelle01]

i just got asked about this prac for the first time ever, must have missed it at this school last year, and my previous school must have done it after I left...so i am anxiously reading this thread so I can know (or try and know) what I am doing,.

Will smiling and nodding help????

[smiley]

Narelle,

After trying many different ways, I can say that pouring it to a 3cm depth in an ice cream carton worked really well for me! We tip it out and kids use rulers to cut it up into 1cm, 2cm & 3cm cubes. Then I use beakers for the acid, and all 3 cubes usually fit into a 250mL beaker just fine.

[Ocker]

Because of the price of agar after trimming blocks
Took all the offcuts and sliced finely placed in a beaker covered in gladwrap then put in microwave for 30sec bursts swirling in-between heats it melted nicely able to recast worked perfectly

[J]

Yes I've kept the leftovers in the fridge for ages and reheated when required. Worked well.
Julie

[Narelle01]

My HT is going to run thru it with me!!

when you say recast - is that for the same prac?

[Ocker]

Yes! just re-melt and pour into moulds
If colour has gone off just add a bit more NaOH

[Rita]

Tried the agar in the dropper trays Thursday for the first time....without dividers.
Lined the trays with glad wrap as I usually do so no problem getting agar out.
Stuck part of a transparent copy of grid paper on side of trays for the heights needed......made tray of 3cm, 2cm and 1cm. The 1cm agar can also be cut down to 5mm if wanted. Enough agar for the two classes. Worked well.

Maths students do a SNAP test. They are given transparent sheets with protractor, 5mm grid and 1cm grids on them. We were given some and we make transparent copies and use regularly in classes. These sheets are ideal for cutting the agar to size.

Rita

[lizzieb]

Have just given out my first batch made in dropper trays as per this thread.

Thank you! Turned out perfectly, and so easy for them to cut into sizes.

Both teacher and I are very pleased.

Cheers