This Christmas season I have been sick with mostly a cough that does not want to go away. A number of days ago I bought a Vicks vaporizer to raise the humidity in the room I was sleeping. The instructions said black particles could appear in the water tub after a while. The device seems to work by extending a column down into a tub of water. Inside the column is a heater that heats the water to a point where it turns into steam. A small plume of steam appears about 10 minutes after the unit is turned on. After it had run overnight I looked in the tub and grayish flakes were sitting at the bottom of the tub. These flakes looked like good candidates for the microscope. I am guessing they are small pieces of charcoal used to filter the water at the treatment plant. Why the form into flakes is a question I cannot answer.