Unusual Materials – Rochelle Salt, Thermoplastic Starch

Unusual Materials – Rochelle Salt, Thermoplastic Starch

Rochelle Salt (Piezo Crystal)

Sometime ago my classmate Naama tipped me off to how easy it was to grow piezo crystals (potassium sodium tartrate) so I decided to try to grow some. It can be made from two easily obtainable household ingredients – Cream of Tartar (Potassium bitartrate aka potassium hydrogen tartrate) and Baking Soda (Sodium Bicarbonate aka Sodium Hydrogen Carbonate). You will need to bake the Sodium Bicarbonate for at least an hour at 100ºC at about to turn it into Sodium Carbonate (also known as Washing Soda), during the process of which it will lose its water/hydrogen). Avoid the cheap Baking Soda or Cream of Tartar which might have cornflour or other impurities added to it.

(And as for why Cream of Tartar is called Cream of Tartar, its apparently because it is a white “creamy looking” crystal precipitate that comes out of grape juice and wine that is stored at a low temperature. Its function in baking is to be the acid ingredient which activates the baking soda (base), producing bubbles and a quick fluffy rise in whatever you are baking – as opposed to slowly waiting for baking yeast to react and produce gas. Since the function of Cream of Tartar is to be an acid in the process, that’s also why some baking recipes call for alternative acids such as buttermilk or milk soured with the acidic juice of a lemon to be used together with baking soda…)

Baking the Baking Soda

Cream of Tartar

Heating the Cream of Tartar in a pot of simmering water and adding the sodium carbonate. It does need to be heated up, and when you add it it will fizz or bubble up. When it stops reacting when you add sodium carbonate the reaction is complete. And yes it really, really needs to be heated up in order for the reaction to occur.

Filtering the resultant liquid mixture into a glass

Leaving the liquid to cool outside, as it was about 4ºC outside…
You would imagine that such a small amount of liquid would not have worked well. Well, after that I brought the glass into the room and forgot completely about it for 3 days and suddenly I looked into the glass and was shocked to see a big crystal sticking out of the glass.

A large crystal had formed and had risen above the level of the liquid. Piece of cake I tell ya.

Thermoplastic Starch

Packing Peanuts
Do your packing peanuts smell like popcorn? Have you accidentally eaten or inhaled a packing peanut? As silly as this may sound I recently realized that some packing peanuts are indeed made of thermoplastic starch of sorghum or corn starch origin. An easy way to test if they are of the bio-plastic variety is to put it in a glass of water. If it dissolves, it is starch-based. I realized this after I observed out loud that the peanuts smelled edible, and then my classmate Tom put the packing peanut into his mouth (and after that he did not roll over with indigestion or die).