I gave a ten-minute speech with PowerPoint slides. It was a technical mystery story called the “Case of the Corroded Computer.”
Almost twenty years ago there was a luxury car dealer who was getting ready to move into a remodeled vintage building in a state capital. Everyone was in a big hurry to get the move completed.
The last step before moving in the cars and the shop equipment was having a contractor come to clean the white tile floor for the showroom. The contractor was told it was OK for him to use hydrochloric acid on the discolored grout, so he did.
On the next day the dealer called and accused him of destroying a brand new minicomputer located in the bookkeeper’s office. The contractor said that was impossible, since his crew had not even been in the carpeted bookkeeper’s office, and the door had always been locked.
The contractor called his insurance company, and they sent a claims adjuster out. She wanted an independent technical evaluation of the damage. A chemist and I went to look at the computer. All the screws on the case were rusty brown instead of shiny silver color. Chemical tests on the motherboard revealed exposure to hydrochloric acid (HCl).
How did the acid (HCl) get there? The building had a forced air heating system. A furnace was located in the back of the showroom, just outside of the bookkeeper’s office. The cold air inlet was located just a few inches above the tile floor. The very first hot air outlet from the furnace led right into the bookkeeper’s office. Unfortunately that outlet was located on the wall directly above the computer, so it got an acid vapor bath. Oops!
After our report the insurer for the contractor bought the dealer a new computer. They got the “old” one to salvage. By hindsight the computer should not have been there yet.
Back in November 2008 I told this story to another group of younger students (4th to 6th grade). I had updated one of my slides to include the molecular weight for hydrochloric acid (36.4), and those for oxygen (32), nitrogen (28) and air (29). When I asked these high school students if hydrochloric acid vapor was lighter or heavier than air, several immediately said it was heavier because it had a larger molecular weight than air.
I forgot to mention to either set of students that the preceding story resembles a Sherlock Holmes story about murder in a locked room, called the Adventure of the Speckled Band.
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