Monday, January 17, 2011

Why was he measuring RI?

The story is often told of discovery of poly(cyanoacrylates) aka Superglue. Harry Cover had recently synthesized some of the stuff and went to measure the refractive index of it. As he was using an Abbe refractometer, the liquid quickly adhered the prisms together [*], ruining the instrument.

The question I always have had was why was he measuring the RI? I've synthesized a nice amount of polymers and have never measured RI for any of them. I always figured that because it is such a trivial test to run even back in the 1940's, it was routine because the many other tests that we now take from granted (FTIR, NMR,...) didn't exist back then (or were difficult to carry out/analyze...)

I think I was finally able to hypothesize an answer when I was reading about Mr. Coover receiving the National Medal of Technology last year: he was trying to develop materials for gun sights. And then suddenly I gathered the rest of the story. Gun sights are lenses, and lenses function based on refractive index and that would then be perfectly logical reason to measure RI, even today.

The other question I have is what was the numerical value of the measurement? Gluing the prisms together certianly would not prevent making the measurement; it would only hinder making subsequent measurements.

[*] For those not familiar with this device, a few drops of the liquid being measured are placed on the lower prism, and then the upper prism is lowered on top of it. The measurement is actually of the angle of total internal reflection, and details can be found elsewhere, but NOT the Wikipedia article which is really poorly written and refers to nonexistent illustrations.

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