Weekend mediumreads: the chemistry of recording

Also in this week's C&EN, I have been remiss in not mentioning a really great article by Matt Davenport about the chemistry of recording, starting with Thomas Edison (a boyhood hero of mine) and wax cylinders, going forward to modern vinyl records:

Using these documents, Monroe is tracking how Aylsworth and his colleagues developed waxes and gaining a better understanding of the decisions behind the materials’ chemical design. For instance, in an early experiment, Aylsworth made a soap using sodium hydroxide and industrial stearic acid. At the time, industrial-grade stearic acid was a roughly 1:1 mixture of stearic acid and palmitic acid, two fatty acids that differ by two carbon atoms. 

That early soap was “almost perfection,” Aylsworth remarked in his notebook. But after a few days, the surface showed signs of crystallization and records made with it started sounding scratchy. So Aylsworth added aluminum to the mix and found the right combination of “the good, the bad, and the necessary” features of all the ingredients, Monroe explains. 

The mix of stearic acid and palmitic is soft, but too much of it makes for a weak wax. Adding sodium stearate adds some toughness, but it’s also responsible for the crystallization problem. The aluminum stearate prevents the sodium stearate from crystallizing while also adding some extra toughness. 

It would be interesting to take a look at the notes of early chemical formulators like Aylsworth to see how much chemical intuition/understanding they had, and how much was sheer trial-and-error.