Phenolphthalein Agar Revisited!!

[Graham Kemp]

Set-up -Mix 1 packet of unflavored gelatin with 1 cup of water, then add a few drops of phenolphthalein, and a few drops of NaOH.
Continue to add enough NaOH and phenolphthalein so that the gelatin mixture remains bright pink after swirling (1%phenolphthalein and 0.2N NaOH work fine). Soak gelatin in acid

I would advise against using gelatine.

It's less cohesive than agar, and melts at 30°C. You might get by in winter, but not in this weather.

[nickykinz]

I do what Graham does with the dropping bottle trays. The cube you get is close to the 3 x 3 and then i just give out more cubes and the students cut them them selves to get the smaller ones. I give out Stanley knives to cut with and white tiles to cut on. If you have a fairly firm agar it works well. Mine always used to be too squishy but I upped the amount of Agar and make sure it is well boiled and it works well now.

[AmandaDLG]

Im having trouble makeing Agar Gel. It never sets. Ive been told to let boil, not let it boil..
I normally do 500Ml of distilled water. put on hotplate and let it heat up then ill add the agar. I was putting 4-5grams then somesaid I should put 10-15grams. Today i put 11grams. I keep stirring for a few mins then put in an automatic stirrer. After 2 -3 mins i put in some vegemite. (about the tip of a teaspoon) i leave it say 4 and let it cook. when it looks like its melted and not boiling I lent pour into New petri dishes. WHAT AM I DOING WRONG. The I have is AGAR 1000 GEL - it was bought in 2012. Other bottles of Agar we have in the cupboard is - AGAR 750 bought in 2010 and 1 bottle of AGAR AGAR (BACTERIOLOGICAL) HELP

[Labbie]

Please Amanda do a search top left hand corner for Agar plates etc, their are so many of those threads for you to choose from.

[AmandaDLG]

Ok Thanks. Never used this website before

[Labbie]

Amanda I will have a look tonight at home, Welcome to Chemtalk, I changed my recipes for Agar plates after reading about it on this great site. Heat your distilled water in the microwave, until about 60c or more, add the agar etc, return to stirrer and keep stirrering. Once all mixed up, I put in a bottle in the Microwave, and boiling until the very large bubbles come up. Let if cool down before pouring. But I will look tonight for you, and try to merge the posts.

[lada]

I make up 3-4% agar, so 15-20g into 500mL of water.
I dissolve agar in cold water and because we have an autoclave, I do not boil it. bring to about 70oC and put in autoclave.
11g should have set.
Lada