July 07, 2016 at 10:43PM

Today I Learned: Here are a couple of TILs I've been hoarding over the last couple of days while I waited for internet: 1) US government bond interest rates are some of the best in the world, despite being solidly less than 2%. Many countries' government bonds actually pay *negative* interest -- they're basically a way to store your money very, very safely, for a small fee. 2) There are two "kinds" of ultraviolet (UV) light, called UVA and UVB. UVA is higher wavelength, closest to visible light. UVB is lower wavelength, down to 290 nanometers. There are difference in how the two kinds of UV tend to be absorbed in the body, but what interests me is their transmission through glass. UVB is almost completely blocked by basically any kind of glass. UVA will penetrate most basic types of glass, but some kinds (laminated, in particular) are UVA-proof. Why do I care? Well, the old way of visualizing DNA in a gel is to stain it with a dye like ethidium bromide and blast it with a ton of UV light, which causes the stain to light up in the visible spectrum. I've been setting up to do this, but the problem is that it produces enough UV to be quite carcinogenic (not to mention damaging on the eyes). I've currently got the UV source in a glassed-in box, but the UV source can generate either 302 nm (UVB) or 365 nm (UVA) light. Fortunately for me, ethidium bromide absorbs at 302 nm, so as long as nobody ever switches on the other setting, I'll be fine. 3) You can make a really compelling supersaturated solution demonstration out of sodium acetate (the salt you get when you combine baking soda and vinegar). You can melt a bunch of it and cool it to room temperature, and if you do it right it should stay liquid until you give it some solid crystals to nucleate around. You can try dusting your finger with some sodium acetate crystals and sticking it in the solution -- it will quickly coat your hand in what looks kind of like ice, but is actually quite warm (the freezing reaction, like all freezing reactions, releases heat). This stuff is colloquially called "hot ice".