Platolum Alloys + Prussian Retailers = Practical Thinking?

I’m reading the investment column in Victory Streak and there’s two things I don’t understand. I can’t tell if they’re meaningless or if it’s because I have absolutely no familiarity with finance...

1. In the subhead “Platolum Alloys + Prussian Retailers = Practical Thinking?” what does ‘Prussian Retailers’ refer to?
2. The last line of the article: “remember oil and carpets, two industries that enjoyed temporary fortune, then plummeted.” This has the cadence of a joke or an idiom... but it’s inscrutable to me. Anyone know what it’s referencing?