"What's its temperature coefficient like?" That reminds me of a common practical joke from EE lab in college (~30 years ago): take the "right" value of carbon

"What's its temperature coefficient like?" That reminds me of a common practical joke from EE lab in college (~30 years ago): take the "right" value of carbon resistor (probably 1/4 watt, I forget how resistance mapped to time delay), plug the leads into an ordinary 120v power outlet, and walk away. As the current flows through it, it'll warm up a little. Because carbon resistors have lower resistance at higher temperatures, as the resistor warms up, it'll start conducting more current, which will make it warmer, until a few seconds or minutes later (depending on resistance value, ambient temperature, etc.) ... "bang!".