The mercury beating heart is an electrochemical redox reaction between mercury, Iron, sulphuric acid and chromium.

Experimental sonification of the mercury beating heart.

Collaboration with Andrea Sella, UCL, First demonstrated during the event Elements at Welcome trust April 8th 2011

See film of reaction...http://vimeo.com/16480939

See laser projection film...http://vimeo.com/23680704

In our experiment a droplet of mercury is placed in a pool of Sulphuric acid [the electrolyte] with chromium [the oxidising agent] The iron is provided by carefully placing the tip of a paper clip into the solution so it just touches the droplet. When contact is made between the paper clip and the droplet there is an exchange of electrons causing the surface tension of the droplet to change, and so changing its shape. This immediately causes the droplet to twitch. Manipulating the position of the clip it is possible to make the droplet oscillate and pulsate autonomously.
The surface of the mercury droplet oxidises [to mercury sulphate] causing the droplet to flatten out. When the clip makes contact with the mercury surface it oxidises, reducing the oxidised mercury surface back to metallic mercury, causing the droplet to return to its more rounded shape, thus loosing contact with the clip. And so the droplet begins to oxidise again starting the process over. Careful placement of the paperclip results on a continually oscillating droplet.

From our experiments, augmented with a reflecting 70mw laser, and 2 photo sensors to sonify the reaction, we observed sonically and visually several oscillatory states;
A fresh reaction, to which a few drops of sulphuric acid may have been added leads to a fizzing on the droplet surface, one is able to see a dull layer forming and breaking up, even a directional rushing of fluid over the surface inducted by this reaction. The droplet tends to easily be coaxed into a rapid irregular twitching. The sound reminded us a lot of a baby’s heart.

From this point it will then settle into the larger maximal low frequency pulse whereby the droplet appears to undulate between triangular and hexagonal modes.
Later on the droplet seems to settle out into a steady pulse where there is little deflection in shape. In our experiment this sounded a lot like a helicopter.

The laser not only enabled up to listen to the sound of the beating heart, it created a fantastic projection. Several different effects are achieved by placing the laser at different points on the droplet.

**CAUTION: It is easy to accidentally reflect the laser back into your eyes during experiments as the mercury droplet will easily slide about, its mirrored surface could reflect the full power of the laser back into your eyes**

Between oscillations we noticed some interesting optical effects as a result of the diffraction and refraction of the light around the curved surface of the droplet into the liquid pool. Notably microscopy effects as well as an excellent display of ‘Newton’s rings’ gradually emerging as the droplet settled between oscillations.

See laser projection film...
http://vimeo.com/23680704

http://www.wellcomecollection.org/whats-on/events/elements/mercury.aspx

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