Fantastic!

The Sarcastic Brit has been working diligently on the new sealing method for our sample holder. This brought on a visit from the host of projects past. Somehow, I never remember how brilliant people were. At least not at the Mecca. Perhaps that is because the inexplicably stupid seems to reign supreme. Perhaps it's just the brilliant engineering doesn't make for very good stories.

Back in the early days(before we realized how bad Captain Fantastic actually was), I remember having many discussions regarding the sealing film that had to go over the sample to prevent evaporation. Our sample is mostly water, which boils at 100C, last I checked. We are heating it to 95 degrees, which is pretty close to boiling. For those of you not keeping track, that means that the the water vapor is exerting nearly an atmosphere (15PSI) worth of pressure on the inside of the sample holder. In addition, there is a bunch of air dissolved in the sample, which is good for an additional 5PSI, or so - I don't remember the exact numbers. When you work it all out, you get a total of about 20 pounds per square inch pushing from the inside of the sample holder.

Captain Fantastic didn't see this as a problem. Apparently, the fact that each well in the sample holder was only 0.0001 square inches meant that the sealing film would definitely hold. After all, that means that each well only sees 0.0015 pounds (or about 0.7 g) of pressure meant that there was no way that the glue would fail to hold.

Strangely enough, every other instrument uses a great big plate to hold the film to the top of their sample holders, with hundreds of pounds of pressure. Apparently, Captain Fantastic forgot to count the wells. The design called for 33,000 of them in the sample holder. By my math, even at 0.0015 square inches per well, works out to 52 pounds of force pushing on a 3.5 by 5 inch piece of tape.

Not only that, but people use hot water vapor to remove adhesive. They rent things called wallpaper strippers. Hmmm... steam. How about removing stamps from envelopes? Hmmm... steam. I bet that hot steam would be pretty effective at removing the adhesive from the top of the sample holder too.

We mentioned this to Captain Fantastic, and he started going on about "peel" stress, and how the glue was really strong in tension, but not in "peel". As far as I have been able to determine, there is no such thing as "peel force". And, of course, the plastic blew off the sample holder the first time we tried it.

It was OK though, both the Captain and Slimy Indian Barbapapa were convinced that the glue would hold. The CTO was backing them up. We must have tried fifty glues of various types. It should have been no problem to find a glue that was transparent, chemically inert, non-fluorescent, and able to give a totally airtight bond capable of withstanding 20PSI of hot water vapor. Of course, we never found one. Every now and then, however, I am asked why the instrument is designed as it is. My response is always "because the glue will hold of course."

As an interim solution, I found a way to hold the seal on a sample holder 1/6 the size. That means that I only had to push down with about 50 pounds of force. No problem, right? And, it had to be designed to fit into the instrument without significant modifications, and it had to be finished in less than three weeks. No problem. Not impossible, but definitely improbable. I accomplished the improbable. Did I get a medal for fixing another one of Captain Fantastic's spectacular derailments? Nah - nobody even noticed that there was ever a problem.