Hydrogen selenide

G’day; Niels of Denmark wrote about the use of a selenium
compound for blackening metals, and there is absolutely no doubt
that this is excellent for the purpose and even better than liver
of sulphur.

But I would like to offer a little warning. Selenium has very
similar properties to those of sulphur, and hydrogen selenide is
a very similar gas to hydrogen sulphide - you know, the rotten
eggs stink of liver of sulphur. H2Se also has a very bad smell,
and is even more poisonous than hydrogen sulphide, H2S. Like
most other poisons, it is OK to use but you wouldn’t want to
drink selenium compounds (although it is an essential element in
agriculture) - neither would you want to inhale too much of the
gas. Consequently do try and work in a well ventilated situation.
When I use potassium or calcium polysulphides for blackening
silver, I do it out in the garden - as much as to keep the peace
with the Chief Cook as anything, for, although she too worked in
laboratories, she objects to our house smelling like an old
fashioned undergraduate chemistry lab! (or a malfunctioning
sewage plant!)

Perhaps I should mention that before the invention of modern
instrumental methods of chemical analysis, hydrogen sulphide was
extensively used. Indeed, it was essential for the analytical
separation of the metals and all such labs positively stank of
it! Cheers, and good scents to you.

    /\      John Burgess
   / /
  / /      Johnb@ts.co.nz    
 / /__|\
(_______)  And Mapua, NZ is a pleasant spot even in