I've always been interested in crystals: their outer beauty hints at a certain kind of inner beauty, caused by the orderly arrangement of molecules at the atomic level. When I was a kid, I made crystals from sugar, salt, alum, and copper sulfate, but never tried Rochelle salts. Rochelle salts are interesting because they are piezoelectric: in response to mechanical deformation, they generate an electrical current. Similarly, when stimulated with an electric current, they deform. This makes them useful for all sorts of cool applications such as microphone pickups.
In an attempt to give you some value added, beyond just the link, I did some searching on Google Books. Somewhat interestingly, it turned up the Nov 11, 1946 issue of Life magazine, which ran an article on Rochelle salt crystals, which had the tag line:
ROCHELLE SALT CRYSTALS
Pretty girls in sunsuits grow a unique mineral that can turn pressure into electric current
Perhaps of greater interest to the experimenter is this article from Popular Science, November 1945 which talks about the history of microphones in general, and includes a bunch of experiments (somewhat tersely described) which can be done.
Carmen and I just got back from a trip to London, and we had a blast. One of the geekiest things we did while there was to take a day trip by train out to Bletchley Park to see the site of the codebreaking efforts by the British during WWII. As any long time reader of this blog must know, I'm pretty interested in codes and cryptography, and this was a bit of a personal thrill for me.
While we were there, we managed to get demonstrations of a real Enigma machine (very cool) and the modern reconstruction they completed of the Turing Bombe. I shot some video of it using a Canon G11, which isn't all that great (the sound in particular is pretty terrible) but I thought I'd archive it on YouTube in case anyone else found it of interest. If you get the chance to go to Bletchley, I heartily recommend it: we spent four hours there, and it really wasn't enough. Besides the Enigma and the Bombe, they have a reconstruction of Colossus, the first electronic digital computer that was used to break the German teleprinter code that the British called "Tunney". They also have huts filled with many artifacts of the period, including one containing a bunch of radio equipment, dating all the way back to the crystal sets of the 1910s and 1920s to the Piccolo secure modem transceivers that were used in British embassies well past the war. Nifty stuff.
I have some pictures that I'll get onto Picasa sometime soon of related nifty topics.