potassium polysulfide again

From: Judy Seigel <jseigel@panix.com>
Subject: Re: old literatures
Date: Sun, 02 Nov 2003 18:12:32 -0500 (EST)

> Meanwhile, about that "liver of sulfur"... I have at least 5 books that
> define it as potassium sulfide, as do at least two present day chemical
> houses. For instance, Cassell's Cyclopaedia of Photography (1911), which
> perhaps you have heard of, says,

I know more than 5 sources that casually equate potassium polysulfide
and liver of sulfur. But they are not the same chemicals, at least in
today's use of the name. If there is any link between one use to the
other, "liver of sulfur" was a traditional name coming from the years
of alchemy before modern chemistry was established. The "liver of
sulfur" produced today are mostly for pharmaceutical applications and
thus they are made to meet USP standard of liver of sulfur. Such a
material is produced by heating mixture of potassium carbonate and
elemental sulfur in its ring structure. There may be other caustic
alkaline agents like hydroxide. Upon heating, elemental sulfur cleaves
the ring and make polysulfide ions of various lengths. But this
reaction produces several other sulfur compounds, including
thiosulfate and sulfate. This reaction is not carried out to
completion and there is significant amount of potassium carbonate,
maybe small amount of hydroxide, etc. remaining, or carried over from
the initial ingredients. Since the end point of the reaction used in
liver of sulfur production may varies from batch to batch, the exact
constituents of liver of sulfur also vary from batch to
batch. However, what's made for pharmaceutical uses need to meet USP
spec of purification.

Coming back to the alchemy era, I don't know exactly what they were
referring to when they gave the name. But it is hard to believe there
was purified potassium polysulfide. The only ingredient that gives
rise to liver-like appearance of liver of sulfur is potassium
polysulfide. Other compounds present in liver of sulfur are white when
they are isolated. So it is conceivable that this rough name "liver of
sulfur" was applied to the crude mixture, and also to the isolated
potassium polysulfide when modern chemistry became able to identify
the major active component of liver of sulfur. Either case, today's
industrial supply of liver of sulfur is mostly for pharmaceutical
applications and we have more hard, limiting definition of what liver
of sulfur is, with USP as the industry standard.

> POTASSIUM SULFIDE
> Synonyms, liver of sulphur, sulphurated potash, potassium trisulphide,
> K2S3, Molecular weight 174. It consists of amorphous masses with the
> colour of liver and is obtained by fusing together sulphur and potassium
> carbonate. It is very deliquescent, and absorbs carbonic acid from the
> air and gives off sulphuretted hydrogen. It is used to precipitate silver
> sulphide from spent "hypo" baths. Its old name was potassa sulphurata.

This definition above is confused. Potassium sulfide usually refers
only to the smallest member of members of potassium
polysulfides. Potassium polysulfide(s) with or without an s refer to a
family of sulfur compounds of varying number of sulfur elements, and
thus potassium sulfide is a compound with one sulfur. I can only see
that the author of that description did not have systematic
understanding of sulfur compounds, or s/he did cut and paste work by
pattern matching the word without going to what the name actually
referred to. I am not necessarily criticising the author of the
description because they might not know the nature of liver of sulfur
at that time like we do today. But I certainly don't recommend anyone
to use what it says as a source of information for today's use.

--
Ryuji Suzuki
"Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)