Ace wrote:

Question: Out of all the lubricants available, even 50+ years ago,
why sewing machine oil? HAZMAT info says sewing machine oil is pure
"mineral oil". My observations are that medical grade "mineral oil"
for internal consumption purchased at a pharmacy does not evaporate.
Sewing machine oil does. Are they different?

Based on an incident that happened several years
ago, I've avoided drugstore "mineral oil" for any
sort of technical application.

We had a manifold with several high pressure
transducers mounted on it. We were gathering
data for temperature compensation tables. We
would apply a specific pressure with a deadweight
tester then vary the temperature of the transducers
in a thermal chamber while logging and plotting
the outputs. We were using "mineral oil" as
the working fluid.

I got a call at 9pm from the project leader. He
said all the transducers had died at -30 degrees
C. As we were far behind on this project and it
was a make-or-break project for the company, I
came in immediately.

It didn't take me long to find that there wasn't
anything wrong with the transducers, but that at
-30 degrees C, the mineral oil had changed consistency
to something more like a cross between slush and
Vaseline. Rinsing and refilling the system with
Mobil1 5W10 (the best thing I could find nearby at
that time of night) fixed the problem.

So what's in mineral oil? Water? I don't know.
I just don't like the stuff any more.