# What is the grey film/black sludge from mercury? How to remove it?

How to remove it? Any other simple method apart from distillation.

I have a small container of mercury that I’ve collected over the past decade. I opened the container after a few years now and I noticed that there is a grey coating on the surface of mercury. Also there is a black powdery deposit at the bottom. It sticks to the bottom and sides of the plastic container.

• There is also chance that the mercury you stored was contaminated with other metals. In this case they might react with air, forming oxide powder. If you are lucky, they might dissolve in acid. However, the resulting solution must be assumed to contain mercury, i.e. considered a toxic waste. Sep 3 '17 at 7:40
• Out of idle curiosity, what did you decide to do with the mercury? No need to answer if you prefer not!
– Ed V
Apr 29 '20 at 18:47
• @EdV No problem sure I can tell you. I eventually figured out what was the issue. So, about 2 months after I had posted this, I got another small batch of mercury and in the same type of glass bottle container. The bottle used to store both the contaminated one and the new one was the same and its laboratory type. The new one is exactly how I had stored it. Well maybe a little less shiny due to mild oxidation. But the other one still sticky and It coats on the glass walls and the base of the container...contd Apr 29 '20 at 19:31
• The reason was my friend who was playing around with it while I was showing him, had transferred it to a watch glass to take a better look. But unknown to me he had used some aluminium rod to touch its surface and then later we had transferred it back to the bottle. He didn't know about the amalgamation process. I guess I might distil it off someday to get pure Hg. Apr 29 '20 at 19:32
• Ah, aluminum reacts vigorously with mercury, once the oxide coating on the aluminum is breached. In WW II, the allies actually considered doing a covert operation to sabotage German aircraft by putting mercury amalgam on the fuselages. So that explains the stuff that that you are seeing. Thanks for the information!
– Ed V
Apr 29 '20 at 19:40

## 1 Answer

First, I would advise against using mercury in a home lab due to the ease which scattered droplets fall into cracks and evaporate.

That said, if distillation is out, then try bulb-pipetting from the center of the mass of mercury to avoid some of the surface contamination. Avoid dropping the mercury when lifting the pipette, since $\ce{Hg}$ is so dense it tends to run out as soon as lifted. Ideally, work in a hood with a large tray with raised sides underneath the apparatus.

If purity is important, electrolysis will yield a higher-grade product... at the risk of working with even more toxic compounds!

Better, get some gallium if you want to play with a liquid metal, and don't need $\ce{Hg}$ to make Grignard reagent or other esoteric substance.