Magpie - 7-12-2006 at 19:27
I need a small amount of H2S as an acidification/precipitation agent in a synthesis I am planning. I have generated H2S before in my
hood using paraffin mixed with sulfur. This worked OK but it left a black insoluble residue in my 8" test tube generator. So I thought
that using FeS might be a cleaner, more controllable, way to go.
My first naive approach was to mix sulfur and fine Fe powder in a mortar in a stoichiometric ratio. I then placed this in an open crucible and began
heating with a bunsen burner. As the sulfur melted I could also see a blue flame indicating that at least some of the sufur was just burning to SO2.
This left me with a black, friable, coarse powder. I knew the conversion would be poor but upon treating with either 6N HCl or 5N H2SO4 I could get
no H2S generation. Then I read in Brauer that Fe and S must be heated in vacuo for 24 hrs at 1000C to make FeS!
My 2nd try was with a ground up piece of iron pyrite (FeS2). Same result, i.e., no H2S.
I have a small amount of aqueous Na2S so tested it with the above acids. Sure enough, good production of H2S resulted.
So, can anyone explain why I did not get any H2S generation with the homemade FeS and the iron pyrite?
Maya - 7-12-2006 at 20:14
Use fine steel wool instead of powder in a test tube and heat, it'll actually light itself on fire once the reaction starts.
works great that way!
[Edited on 8-12-2006 by Maya]
garage chemist - 8-12-2006 at 04:18
Don't heat from below, that just burns off the sulfur. You have to light the reaction like you would light thermite (its easier than with thermite
however).
Again mix Fe and S powder in stochiometric amounts, make a pile out of the mix on a fireproof surface (or in a crucible) and insert a yellow hot iron
wire. The wire has to be held in place after reaction has started. Reaction is slow (maybe 5mm per second, or slower) but very exothermic (mix will
melt and glow red).
Magpie - 8-12-2006 at 14:37
Garage chemist I am trying your method first. I mixed 3.2g S with 5.6g Fe in a mortar. The Fe is a fine powder, probably pyrotechic grade. The S
is flowers of sulfur, USP grade (food grade). I poured this mix onto a large concrete block. I then heated a no. 22 (0.6mm diameter) iron wire to
bright orange using a bunsen burner with MAPP gas. I placed this in the mix. There was some reaction but it wouldn't take off. I then tried a
larger iron wire (a coat hanger) which I measured at 3/32" (2.4mm) in diameter. Same result. My lack of any thermite experience is probably hurting
me here.
I am now firing up my muffle furnace to 1100C in an attempt to get a yellow hot wire. Do you have any suggestions before I make my next try?
Magpie - 8-12-2006 at 17:47
Maya I tried your method while waiting for the muffle furnace to heat up. I placed about 4.5 g of "000" fine steel wool with an excess of sulfur in
the lower half of an 8" test tube. I used the wool like a sponge to "mix" it with the powdered sulfur. I then heated the bottom of the tube with a
bunsen burner until the wool caught on fire. It was rather impressive to watch! When it cooled I easily poured out some black/grey powder along with
a few pieces of unburnt wool. I tested the powder with 6N HCl. It tested positive for H2S. 
Magpie - 8-12-2006 at 20:24
The 2nd try was made with the Fe/S powder and the hotter poker (muffle was at 1050C). I used the 2.6mm dia iron wire and had it inserted about 10 cm
into the furnace. I layed it on the powder pile and left it there. It still would not start on fire.
Garage chemist: It really puzzles me that you can get this to burn but I cannot.
Maya - 8-12-2006 at 22:41
yeah it is pretty impressive that it works so well with steel wool. I learned that experiment when I was 12 or so out of some amatuer textbook. You do
end up with a trashed test tube though and like GC said, light / heat it from the top.
BTW, remember that H2S is more poisonous than cyanide and there is no antidote
[Edited on 9-12-2006 by Maya]