[Histonet] Cleaning Acid (Long)... Aqua Regia Correction?

[John A. Kiernan]

Sorry, my mistake. Well spotted. Aqua regia
is, of course, 3 volumes of hydrochloric and
one volume of nitric acid.
(I have corrected it also in the quoted email
below, just for posterity.)
-- 
-------------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan[AT]uwo.ca
   http://publish.uwo.ca/~jkiernan/
   http://instruct.uwo.ca/anatomy/530/index.htm
_______________________________
"Due, Brice" wrote:
> 
> Hello John, as always, thank you for sharing your knowledge. below you list aqua
> regia as 3:1 nitric:hydrochloric. I have more often seen it as 1:3
> nitric:hydrochloric, and this is what I've used before. Was this a typo or can
> it go both ways?
> 
> Thanks,
> -brice
> Neuropathology Lab
> Brigham & Women's Hospital,
> Boston
> 
> -----Original Message-----
> From: histonet-bounces <@t> lists.utsouthwestern.edu
> [mailto:histonet-bounces <@t> lists.utsouthwestern.edu]On Behalf Of John A.
> Kiernan
> Sent: Tuesday, April 26, 2005 12:29 PM
> To: Scott, Allison D
> Cc: 'histonet <@t> lists.utsouthwestern.edu'
> Subject: Re: [Histonet] Cleaning Acid (Long)
> 
> An answer to a question asked last week about
> cleaning glassware for a silver staining method.
> Skip to the bottom line if you don't want to
> know the reasons.
> 
> Glassware that has been used for silver methods can
> collect traces of metallic silver - sometimes enough
> to see as a mirror or grey marks. If the glassware
> is used again for silver staining, these traces serve
> as nuclei for deposition of more silver, and they
> are bigger than the desired nucleation sites in
> the sections. The staining method may simply fail
> or the chemical reaction may go wild, with nonspecific
> deposition of silver all over the place.
> 
> Silver is soluble in nitric acid. My cleaning technique
> is to put a little concentrated HNO3 in the vessel
> (Coplin jar or larger tank) and carefully move it over
> all the inside surface, over a sink with running water
> so that any spilled drops of acid are quickly diluted.
> Visible silver (look in the corners) disappears
> instantly, so smaller amounts must also be removed.
> Pour the used nitric acid into a beaker containing
> tap water (for later neutralization and disposal). If
> the tap water becomes opalescent you have removed a
> significant amount of silver from the glass.
> 
> Next - and this is important - Fill the vessel with
> PURE (eg distilled) water and empty it; do this twice
> so that the concentration of silver ions in the water
> adhering to the sides is infinitessimal. Tap water
> must not be used for these washes because it always
> contains anions (chloride, bicarbonate, others?) that
> form insoluble silver salts. Any colloidal silver
> chloride particles that stay on the glass will be
> partly reduced to silver by exposure to light and
> can be expected to provide nucleation sites in
> later silver staining methods. Finally dry the
> glassware by letting it drain and store the vessels
> upside-down in a closed cupboard.
> 
> Deposited silver is not the only kind of dirt that
> can spoil silver staining. Any kind of organic
> chemical deposit (such as a fragment of a section)
> or even residue from evaporated tap water will
> work in the same way. Concentrated nitric acid
> quickly oxidizes and dissolves pretty well everything,
> with one notable exception.
> 
> The exception is metallic gold. This can replace
> deposited silver in glassware used for gold-toning,
> a procedure often used to improve contrast in
> silvered preparations. Gold on glass may appear
> only as a light purple discoloration. Any colour
> that resists nitric acid is probably gold. It can be
> removed with aqua regia, which is a 3:1 mixture of
> concentrated hydrochloric:nitric acids. Make and
> use aqua regia in a fume hood because it emits
> fumes of chlorine and nitrogen oxides. I have
> resorted to aqua regia 3 or 4 times (in >30 years)
> to get rid of gold on glass. The obvious way to
> prevent contamination is to reserve certain jars
> and dishes for gold-toning and nothing else. This
> is not very practical if we do many different
> methods and do not have a cupboard big enough for
> all jars that might carry catalytic contaminants.
> 
> Some people use Farmer's reducer (a solution
> containing potassium ferricyanide and sodium
> thiosulphate). This is an altogether gentler
> liquid than nitric acid and it can dissolve silver
> from black & white photographs. The action of
> Farmer's reducer on visibly discoloured glass is
> very slow, and this mixture is not going to
> destroy insoluble organic forms of dirt such
> as bits of tissue.
> 
> Bottom line: Nitric acid, followed by pure (not
> tap) water.
> 
> John Kiernan
> London, Canada.
> ________________________________
> "Scott, Allison D" wrote:
> >
> > Hello to all in histoland.  I need help in locating a cleaning acid solution
> > for cleaning glassware.  We are having a problem with our GMS stain.  I
> > think it has something to do with the glassware.  Thanks in advance
> > Allison Scott
> -------------------------