[Mahmoud]

welcome all
who can make interpretation for this video on youtube

http://www.youtube.com/watch?v=aC-KOYQsIvU

thanks

[Borek]

Not an ice, but nice. Note that you don't just "touch" the solution, there is some crystals on the finger - and they play crucial role here.

[ARGOS++]

Dear Mody175,

This Phenomenon is known as a “deferred/impeded/delayed” Crystallisation or “Oversaturated Solution” and can for other Substances then Sodium-Acetate go quite danger.

As you may know that for almost every substance the solubility in a solvent increases significantly with the increase of temperature the final concentration is several times higher then by R’Temp.
For starting Crystallisation during the cooling Phase it is required that the solution contains a few “Crystallisation Germs”, otherwise the real Crystallisation can not start at the Temperature on which the Solution becomes “oversaturated”.
As soon as any  “Crystallisation Germs” “hit” the “Oversaturated Solution” the spontaneous Crystallisation starts and can get very wild!
Only in the case of Sodium-Acetate the Exothermic is small enough to only warm the “Instant Ice” a little bit.
In most other cases, other Substances, the Exothermic is quite larger and results most times in “re-boiling” of the solvent in that way, that the whole mixture is leaving the “Glass/Flask” in a dramatic way. 
That’s why a good Chemist always controls the cooling process and keeps care, that the solution contains some  “Crystallisation Germs”.
(Remember: It’s not required, that the “Crystallisation Germs” must be of the same material as the final Crystal.).


Good Luck!
                    ARGOS⁺⁺