`MIT undergraduate lab chromic acid disposal practice`

Tom's own student-era recollection (early 1970s) of routine disposal of chromic acid down the laboratory drain after etching glassware. Used to mark how dramatically environmental standards have shifted in his career. ## Figures referenced

When I was a student back here in that little lab across from my office, when we cleaned glassware — we did this in high school too, but we didn't have it quite as big a thing — there was a sink in there, and they had a tank of chromic acid about this big. Whenever you cleaned your glassware, after it was clean and you'd rinsed all the soap off, you would take some tongs and dip it in the bath of black chromic oxide. You'd rinse it off in that, because chromic oxide etches the glass super clean. Then you'd put it under the water and just run the chromic oxide down the drain. If I did that today they'd probably handcuff me and take me away. But this was the early 1970s. Ten years later, Erin Brockovich learned about chromic acid — or hexavalent chrome, as other people call it. This is hexavalent chrome: look at it, CrO3, two times three is six, that's hexavalent. So we don't use these so much anymore. Sulfuric acid you can use, hot fairly concentrated sulfuric acid, or ferrous sulfate. Anyway, you have to have cleaning tanks.