I tried your chemical test, and by your prescription, it's soot. But
I've not turned on the heat (I live in so cal). In my initial online
search of information, I came across the artillery fungus, which is
fascinating, but I think some people refer to the tarlike consistency
of the dots, and I think someone mentioned they are blobby, while
these dots are not tarlike, they do not smear, and they are wahfer
thin. I do have house plants though. Some dots are not in direct line
of sight of plants, but, I'll research this source some more.
There are no other obvious sources I can think of in my environment.
But I am beginning to wonder if I'm wasting your time and that it's
something incredibly mundane right under my nose. My neighbor thought
it looked like glitter, and my memory of how they appeared makes that
unlikely, but maybe my interpretation of it all is faulty. I did have
people over the day before they appeared, and I don't remember anyone
wearing glitter, but hey, could have happened, and by now my feet
would have tracked them everywhere. A friend has a steam cleaner, so
I'm hoping to borrow it and attack the apartment. If I do a thorough
clean of the apartment and they still show up, then it may be
something funny, otherwise, if they don't come back, I've probably
been a silly goose. I'll let you know what happens.
thanks for all your input.