Sciencemadness Discussion Board

Preparation of Vermilion (HgS)

garage chemist - 25-3-2005 at 03:56

I made several experiments to produce the beautiful red pigment from mercury and sulfur, none of them was sucessful.
The first try was to grind together sulfur and mercury in a mortar, because the elements react with each other at room temperature.
The sulfur became very black after a short time, and the black mass was transferred to a beaker and boiled in NaOH solution to remove the sulfur. The sulfur dissolved rapidly and the solution became yellow. But after about 2 days, the HgS had dissolved in the polysulfide solution! Only a small drop of unreacted Hg remained.
On addition of a drop of HCl, a voluminous black precipitate occured, which redissolved after some stirring because of the excess of NaOH.
What happened here? Do I now have a highly toxic soluble mercury compound? I wanted to start with a non-toxic one...
What compound is formed when HgS dissolves in a sulfide solution?

The next try was to melt together mercury and sulfur. 7g Hg and 3g sulfur were added to a test tube, and it was heated. The sulfur melted, and suddenly there was a violent reaction and a black sublimate occured. I heated it further, and more sublimate occured, it looked very strange and there were red, black and metallic looking sections, though I could not see any mercury droplets.
I sublimed the entire HgS onto the walls of the test tube, where it formed a thick hard black deposit.
K2CO3 solution was added after cooling and heated to dissolve residual sulfur.
The sulfur dissolved and the solution became yellow, but this time, no black precipitate occured on addition of a drop of HCl, it only fizzed a bit. So my HgS doesn't dissolve this time, which is good.
I need to get the hard black stuff out of the test tube, it's very difficult to remove.

My question is: why did I get the black modification on sublimation of the HgS?
In ancient times, black HgS was first prepared by melting together Hg and sulfur and the changed into the red modification by sublimating it.
Why does my HgS stay black? Is it possible that it contains finely divided mercury?

(Edit: changed title)

[Edited on 25-3-2005 by garage chemist]

Mr. Wizard - 25-3-2005 at 09:29

You have made Mercuric Sulfide. Apparently it is a black allotropic version (The Moor?) and can be converted by further treatment. I guess you'll just have to use the search engine. Here is a what I found in a short search:

Medieval mystics and alchemists found significance in the manufacture of synthetic cinnabar, or vermilion, from mercury that went beyond producing a pretty color. AS early as the 8th century the mixing of sulfur to mercury, which had been extracted from cinnabar by roasting and condensation, was discovered to produce black amorphous mercuric sulfide, the Moor. Further processing rearranged the molecules to produce a bright red which far surpassed the mineral cinnabar in purity and chroma. To philosophers, the mixing of the liquid, "watery", quicksilver to the "fiery" sulfur to produce "earth", and then through heating change into "blood", was no less than the creation of life in the retort. Such was the nature of their intermingling of mind and substances, and their proximity to art4.

garage chemist - 25-3-2005 at 10:00

In Jander-Blasius I found the following reactions:

HgS + S2- ---> (HgS2)2-
Hg + (S2)2- ---> (HgS2)2-

I used polysulfide solution, so I now have this weird complex.
It further says that when H2S is added to this complex solution, HgS precipitates because the sulfide ion concentration drops (HS- is formed).
HCl should have the same effect, shouldn't it? If I use an excess of HCl, the solution should be free of mercury. Is this true? How can I test that?
But adding HCl will also precipitate sulfur, so I will be left with impure HgS. Maybe the sulfur can be removed by heating it, sulfur boils before the HgS starts to sublime.

On the subject of the red HgS modification: a search yielded the info that the sublimed HgS must be ground in order to bring out the red color. I will try that as soon as I get the stuff out of the test tube and treat it with hot HNO3 to dissolve possible contamination with metallic Hg.

This project now turns out to be much more dangerous than I thought. I wanted to avoid soluble Hg salts until I have better equipment... but now I'm forced to work with them.

guaguanco - 25-3-2005 at 11:22

Yeah, be careful. You're definitely manipulating highly toxic compounds at this point.

m3matthew - 28-1-2006 at 11:53

Hello Mr Wizard,
I had a question about mixing mercury and sulfur to obtain Hgs. If I mix 35 grams of mercury with 95 grams of sulfur in a marbel mortar would the powder that is formed constitute Hgs? If I add a sulfur little by little to the mercury and continue to grind will the mercury become evenlly spread in the sulfur?
If I am wrong about the mixing how can I best obtain Hgs through mixing mercury and sulfur, which method is best?

Mr. Wizard - 28-1-2006 at 17:55

m3matthew, I would be very reluctant to mix Mercury and Sulfur in an open marble mortar. What will keep the fumes from the Hg from rising and poisoning you? I can't guide you on the best way to react these two elements together. I would be careful about opening Mercury in any area in which you are breathing the air. I have never set out to make the sulfide, but only used sulfur to keep the fumes from escaping. Be careful.:o
Do a lot of reading before you do any mixing.

toxin - 29-1-2006 at 17:38

I read somewhere that the black HgS(metacinnabar) turns to red colored cinnabar when heated to 500 deg C