Comments on: Soda fountain science explained http://blog.khymos.org/2008/06/19/soda-fountain-science-explained/ - dedicated to molecular gastronomy Thu, 20 Nov 2008 16:46:13 +0000 http://wordpress.org/?v=2.5 By: Robert Paulson http://blog.khymos.org/2008/06/19/soda-fountain-science-explained/#comment-99124 Robert Paulson Mon, 23 Jun 2008 08:03:55 +0000 http://blog.khymos.org/?p=175#comment-99124 Martin: Surfactant into the soda, recap and agitate by swirling. As the bottle is plastic, an appropriate surface is required for bubble formation, hence, the Mentos or a substitute are required. I also expect that if you coat the Mentos with surfactant there will not be a large change due to the surfactant not diffusing well but remaining localised around the Mentos. I'm not sure though, so will add it to my notes for the next time we do the experiment. Martin: Surfactant into the soda, recap and agitate by swirling. As the bottle is plastic, an appropriate surface is required for bubble formation, hence, the Mentos or a substitute are required.

I also expect that if you coat the Mentos with surfactant there will not be a large change due to the surfactant not diffusing well but remaining localised around the Mentos. I’m not sure though, so will add it to my notes for the next time we do the experiment.

]]> By: Martin Lersch http://blog.khymos.org/2008/06/19/soda-fountain-science-explained/#comment-99046 Martin Lersch Sun, 22 Jun 2008 15:55:21 +0000 http://blog.khymos.org/?p=175#comment-99046 Robert: Did you apply the surfactant to the Mentos or add the surfactant directly to the coke? (i.e. perform the experiment without Mentos) Barzelay: You would be able to dissolve CO2, but this sounds like too much work. Robert: Did you apply the surfactant to the Mentos or add the surfactant directly to the coke? (i.e. perform the experiment without Mentos)

Barzelay: You would be able to dissolve CO2, but this sounds like too much work.

]]> By: Barzelay http://blog.khymos.org/2008/06/19/soda-fountain-science-explained/#comment-98603 Barzelay Fri, 20 Jun 2008 16:18:42 +0000 http://blog.khymos.org/?p=175#comment-98603 What about letting the soda go completely flat, then adding the surfactant, then re-carbonating the soda? Or would the surfactant prevent the carbon dioxide from dissolving? What about letting the soda go completely flat, then adding the surfactant, then re-carbonating the soda? Or would the surfactant prevent the carbon dioxide from dissolving?

]]> By: Robert Paulson http://blog.khymos.org/2008/06/19/soda-fountain-science-explained/#comment-98564 Robert Paulson Fri, 20 Jun 2008 05:48:43 +0000 http://blog.khymos.org/?p=175#comment-98564 What you will find is that there is an exponential limit that the surfactant will get to before unstimulated loss of gas. The nature of the surfactant will merely affect the concentration required to reach the limit. A simple experiment (I have done this with 14-18 year old school children) is to add some surfactant (1 drop) then measure the fountain height. Add 2 drops into a fresh bottle, then measure the fountain. Add 4 drops, etc. Plot surfactant versus fountain height and it will look like a Gaussian distribution. What happens is the change in surfactant changes the width of the distribution, but only slightly effects the height of the fountain. The discovery is that the rate of nucleation is the limiting factor in the system. Roughly breaking the Mentos or rock salt will increase surface area and hence, rate of nucleation. Powdered material slows the reaction as the top of the solution desorbs gas faster than the bottom, leading to longer but less powerful fountains. What you will find is that there is an exponential limit that the surfactant will get to before unstimulated loss of gas. The nature of the surfactant will merely affect the concentration required to reach the limit.

A simple experiment (I have done this with 14-18 year old school children) is to add some surfactant (1 drop) then measure the fountain height. Add 2 drops into a fresh bottle, then measure the fountain. Add 4 drops, etc. Plot surfactant versus fountain height and it will look like a Gaussian distribution.

What happens is the change in surfactant changes the width of the distribution, but only slightly effects the height of the fountain. The discovery is that the rate of nucleation is the limiting factor in the system.

Roughly breaking the Mentos or rock salt will increase surface area and hence, rate of nucleation. Powdered material slows the reaction as the top of the solution desorbs gas faster than the bottom, leading to longer but less powerful fountains.

]]> By: Anonymous http://blog.khymos.org/2008/06/19/soda-fountain-science-explained/#comment-98446 Anonymous Thu, 19 Jun 2008 16:15:18 +0000 http://blog.khymos.org/?p=175#comment-98446 On the Mythbusters episode they tried rock salt instead of mentos, which worked better (more nucleation sites). I assume that another liquid could be used, maybe with higher concentrations or more efficient surfactants than aspartame, gelatine and gum arabic. On the Mythbusters episode they tried rock salt instead of mentos, which worked better (more nucleation sites). I assume that another liquid could be used, maybe with higher concentrations or more efficient surfactants than aspartame, gelatine and gum arabic.

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