Why Did the Old Reactor Work Best?

Why Did the Old Reactor Work Best?
The expected color reaction at a dye manufacturing plant hadn't taken place. Why did the batch still work when moved into the old reactor?
Mysteries of Science


The sprawling GAF plant was upgrading some equipment in their dye-manufacturing department. One of the oldest and most common designs for production reactors is the glass-lined metal vat.

The old vessels were made of cast iron, but often coated with glass or ceramic similar to a porcelain cooking pot. The new reactor was made of a newer metal alloy instead of cast iron, but it was glass-lined just like the old cast iron one.

The first batch was run in the new kettle, but something was wrong. The expected color reaction hadn't taken place and it was long overdue.  This was mystifying.

Why didn't it react in the new unit? Was the new reactor inadvertently adding something? Why did the batch still work when moved into the old reactor?

Here's the rest of the story.

Water was run through the old reactor and analyzed for common chemical elements by atomic absorption, and iron showed up in the test. Where would iron come from?

There had to be a crack in the old glass lining. The old reactor with its exposed iron was catalyzing the reaction.

It only took a trace of iron and the hairline crack was enough. Since such a small amount of iron was being dissolved from the reactor, the reactor was likely to last for a century or more before being depleted.

Armed with this forensic detail, the problem was easily fixed. A trace of iron salt was added to each batch. The old reactor had been adding a pinch of iron for many decades and now the secret was out.


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