CR-Scientific
Minerals & Experimental
Science newsletter
Issue #8HTML version
In this issue:
I. Purification of Sulfuric Acid
II. Qualitative Analysis of Hemimorphite
III. Microscopic Examination of Common Fungi
IV. Site News
While the information in this newsletter is thought to be accurate to the best of the authors' current knowledge, it is not guaranteed to be free of errors or to be suitable for any particular use. The procedures and experiments outlined within can be dangerous or even fatal if carried out improperly. If you choose to attempt any of them, you proceed entirely at your own risk.
I. Purification of Sulfuric Acid
Of the
three
"mineral acids" (HCl, HNO3, and
H2SO4), sulfuric acid may appear the least useful
for
mineral analysis, but it is indirectly very useful in that it can be
used to
prepare the other two when small quantities are required and no supply
of them
is on hand. There are
two grades of
sulfuric acid the avocational scientist is likely to encounter. The
first is
the "electrolyte" grade, which is a 30-50% solution of sulfuric acid
in water. The second type is the concentrated (95-98%) commercial grade
which can have a deep brown color due to extensive impurities,
especially iron. This
latter grade of sulfuric acid makes an effective-but-nasty rust remover
when
mixed with phosphoric acid, though it is not directly useful for
preparative
chemistry or for analyses.In either
case, the
experimenter finds strong temptation to pursue the same goal: a final
product
consisting of concentrated sulfuric acid with as few metal-ion
impurities as
possible. The desired liquid is pale yellow and appears oily.
This article is not a
recommendation to do any of
these procedures; it simply gives the amateur scientist some
idea of
what could be expected-- including the dangers. The best recommendation
is to
locate a source of reagent-grade sulfuric, nitric, and hydrochloric
acids, so
that one is never tempted to engage in unnecessary re-distillations.In the
first case, that
of the 30-50% sulfuric acid solution, the concentrated end-product
would be
attained by simply boiling off the water in an outdoor area.1 When a
beaker of the acid is heated on a
hot-plate, the temperature will climb until the liquid eventually
boils,
somewhere around 100 degrees C. It is heated until the boiling stops
and the
temperature starts to climb again; when the temperature goes above
ca. 140°C, the acid is removed
from the heat. Sulfuric acid has an extremely high affinity for
water, so
it will still have at least 1.5 to 2% H2O. More
likely it
will be about 4-5%. Depending on whether this material is also
contaminated
with metal ions or not, it could then be distilled as if it were the
highly
impure but concentrated grade mentioned previously. If the color is
pale
enough, it can be used as-is.If one
were to continue
heating the acid after the first boiling stopped, letting the
temperature climb
well above 100° C, the liquid would start to boil again (somewhere
over
300° C). The "steam" this time would consist almost entirely of
sulfuric acid vapor. For the
second type of
sulfuric acid, the concentrated but iron-contaminated commercial grade,
the
procedure would involve distillation of the sulfuric acid. Yes, the
author has
done this, and no, it is not a good idea.
It is
slow and consumes a great deal of energy, thanks to the high b.p. of
sulfuric
acid; and it is dangerous, thanks to the extremely
corrosive nature of the hot
acid and its vapors. These materials are alright if they stay inside
the
glassware 2,
but there's always the
small but real chance that any given piece of glassware will
shatter
during heating. If this were to happen, the consequences would be
horrible to
persons standing nearby. Room-temperature sulfuric acid may take a few
seconds
to attack the skin, but hot sulfuric will corrode it instantly.For anyone
willing to
accept the substantial risks associated with distilling the mineral
acids, it
is at least preferable (1) to use all-glass apparatus so that H2S
and other compounds from rubber stoppers will not contaminate the
product, and
(2) to do the procedure outside, in an area away from things and people
that
could be harmed in case of an accident. It is also wise to do acid
distillations on no larger a scale than necessary. The mineral
acids are
entirely unforgiving; mistakes can kill, blind, or disfigure the
careless. A
face shield, goggles, adequate ventilation, and a nearby emergency
shower are
not optional- they are required. Do not allow any person or object to
block
one's path to the emergency shower. Back to the distillation, should one be so inclined as to pursue it anyway. Concentrated sulfuric acid forms a constant-boiling solution of about 98% acid and has a b.p. of 338° C 3. With the non-volatile impurities, the actual b.p. will likely be somewhat above this temperature. Once this temperature is reached, dense fumes of H2SO4 vapor will fill the flask. When they go through the cooled coils of the distilling apparatus, they will recondense into liquid H2SO4, minus the metal-ion contaminants. The color will be much, much lighter than the molasses-brown acid with which we started. It is this distilled acid which would be used for laboratory preparation of HCl or HNO3, as well as for qualitative analyses which may directly call for sulfuric acid.
If there
are any
volatile impurities in the starting material, they will come over into
the
final product. For example, any chloride ions present in the raw
material will
form HCl, which will end up in the "purified"
H2SO4. Always
follow the usual
precautions of not adding water into the concentrated acid, not letting
the
concentrated acid touch paper, wood, sugar, cloth, skin, etc, and
always
wearing thick polyethylene gloves and a set of safety goggles. II. Qualitative Analysis of Hemimorphite
The following article was written and submitted by Mr. Dana Morong. It is an interesting and concise account of how he used the classic mineralogy techniques to test a mineral sample.
Please note: as with all other information on this website, the reader assumes full responsibility for any consequences that might arise if he / she chooses to attempt the procedures given herein. We cannot control what you do or how you do it; therefore, neither we nor the author(s) accept any responsibility for what may happen as a result.
I had
given to me a few
small specimens by persons cleaning out rooms, and whereas most of it
was
chalcedony, there were some crystals that were not, and I was curious
as to
what they might be. These were clear, longitudinally striated crystals,
many in
subparallel sprays, and were on a limonite base (I don't know their
locality,
although I suspected either the S.W. U.S. or Mexico). The
crystals in this
mystery specimen reminded me of something, but I couldn't quite seem to
remember where I had seen crystals like these. Perhaps if I had looked
up in
the books and in The Mineralogical Record I would have found
them. The best
first test is
visual, using a low-power microscope if necessary, but I had been so
eager that
I first took a spare specimen to the lab to test chemically. I crushed
a bit of
sample into fragments. Before the blowpipe it was infusible, turned
white and
opaque, and on charcoal turned yellow when hot and white when cold.
Infusible,
hence not cerussite, as that yields lead before the blowpipe flame.
Treated
with cobalt nitrate (one drop upon the oxidized sample on charcoal),
then put
"B.B." (Before Blowpipe, as in the old books) again, this time the
fragments were blue, but no coating on charcoal. Of course one can get,
in this
test, blue with many fusible minerals, as the slag absorbs the cobalt,
but in
the case of an infusible sample, it can indicate zinc or aluminum, and
this
sample was infusible, at least in the flame that I could produce. I was
surprised that
this should be infusible, but thought to test for silica by a Salt of
Phosphorus bead test. However, before making bead tests, it is wise to
first
determine whether a sample contains any arsenic (or antimony or other
semi-metal which can damage the platinum wire), so I put some powder
into a
closed tube to test (closed tube tests are useful to test for arsenic
and such
as they can show evidence of such ions which can harm Pt wire). I had
added a
bit of charcoal to reduce any possible arsenate to arsenide (I have
used this
in the past to test scorodite), but other than a bit of water there was
no
sublimate in the closed tube, although the sample decrepitates. I dropped
some of the
powder into a test tube and added a little bit of acid from a jar that
said
"5% Nitric Acid" (I hope the label is correct; I actually do not use
acid straight from the stock bottle but put some into little labeled
dropper
bottles for use, which is convenient as one can use the dropper, part
of the
cap, to measure out a few drops up to 1 cc or so). Some carbonates
require
powdering or heating to effervesce in acid, and cerussite works best in
nitric
acid, and I had a bit of this anyhow so used it. The powder did not
effervesce
in acid, so I warmed it slightly (it must be heated gently so that boiling does
not spatter the entire contents out of the test tube - usually I slant
the tube
away and warm it just to boiling, then back off. Boiling stops bubbling
when
source of heat is removed, and is not the same as effervescence, which
would
continue4).
There was no carbonate in
this sample, but it didn't take long for the sample to entirely
dissolve into
solution. Now I had
a solution to
work with, and I separated it into tiny amounts, tried Potassium Iodide
on one
(no reaction, no lead), Barium Chloride on another (no reaction in acid
solution, hence no sulfate), but when neutralized with ammonia it
yielded a
white flocculent "precipitate" which doesn't really fall out of
solution, but looks cloudy and thick, and can indicate various ions,
including
Al and Zn. The Salt
of Phosphorus
bead test was somewhat helpful, although it takes a bit of experience
with
silica to tell whether such may be present, as silica is one of the few
mineral
constituents not soluble in Salt of Phosphorus bead and therefore will
show
"skeletons" of the grains as the bases are dissolved leaving the
silica behind (there are a very few non-silicate minerals also not
soluble in
this flux, but these can be memorized and besides don't look like
silicates.
Also, a few zeolites may be somewhat or slowly soluble in the flux, so
these
are silicate exceptions to the rule). This sample was not very soluble
in this
bead, or perhaps insoluble, indicative of possible silica. Going back
to the sample
treated before the blowpipe on charcoal, the coloration of the sample
(yellow
when hot and white when cold) is so typical of zinc (and of lead,
except that
lead has been eliminated as a possibility by now), that one would have
expected
the green coloration of zinc with cobalt solution, instead of the blue
color of
fragments. By this time I was suspecting zinc silicate, or
hemimorphite, and
had eliminated several other ions as non-possibilities. So I turned off
the
Bunsen burner (never leave a flame unattended) and went upstairs to the
library, where I looked up in Plattner's Blowpipe Analysis (an
edition
of 1875) and in Dana's System of Mineralogy (6th edition of
1892), which
said that hemimorphite does not respond well to the cobalt nitrate test
for
zinc, unless one mixes a flux, such as soda (sodium carbonate), or even
better,
a mix of soda and borax, with the sample and then treat it to the
oxidizing
flame of the blowpipe. As this species is infusible, or nearly so, the
flux
helps to break it down so that the zinc can be oxidized. So I did this
and got
somewhat of a green coloration, typical of zinc, although the test was
not as
neat as usual, possibly because I had used a bit more material than
could be
conveniently melted in the flame of the blowpipe. It is better to be
moderate
in amounts, particularly with the blowpipe, which although can produce
a hot
flame, it has only a very small flame, so the heat is quite localized.
This is
useful for tiny samples. All of
this interesting
and diverting experimentation showed that this was a zinc silicate,
which
should have been apparent at the beginning, as when I put the other
specimen of
the very same material under the low-power microscope, and consulted
the books,
the crystals had the very same shape, angles, habit, and morphology as
those of
hemimorphite. I had done things a bit backwards, testing first and
microscoping
afterward, whereas it is usually best to first visually examine the
specimen,
gather all the data one can get by visual and non-destructive testing,
and then
afterward, when one has mentally narrowed down the list of remaining
possibles,
submit a bit of spare material to physical tests (hardness and cleavage
can be
very useful tests, even on material viewed under the microscope; one
may use a
needle mounted in a handle to test for hardness) and to chemical tests,
and
thus either confirm or deny hypotheses. However, as one test may not
always be
confirmatory, and two or more may show up possible error, it can be
useful to
use more than one test. Some say that these tests are best only on
non-silicates, and some therefore don't attempt tests, but I have
tested over
three dozen non-silicates from the New England region (famous for some
of its
silicates, although there are many non-silicates also), and there are
minerals
from other regions that also need help in identification. It is odd
that some
collectors place so much confidence in instrumental tests but won't do
a
simple, chemical test. In an article on the Loudville (Massachusetts)
Lead
Mines, the authors had mentioned that "Specimens of purported cotunnite
owned by micromounters have been x-rayed and identified as barite."
(Dunn
& Marshall, 1975). If someone had a bit of extra to test,
solubility would
have shown that lead chloride (cotunnite) is slightly soluble and
barium
sulfate (barite) not at all, or very insoluble, in water and in acids.
It can
be thereby useful to take to heart the advice of Dunn (1993) and try a
bit when
one can. References:
DANA, James D. & Edward S., 1892, System of Mineralogy, 6th edition.
DUNN, Pete J., 1993, "Mineral Identification in the Home Laboratory: Some Useful Techniques". Mineralogical Record, January-February, v.24, #1, 3-10.
DUNN, Pete J. & MARSHALL, John H., Jr., 1975, "The Loudville Lead Mines". Mineralogical Record, November-December, v.6, #6, 293-298.
POUGH, Frederick H., 1976, A Field Guide to Rocks and Minerals (any edition will do).
RICHTER, Theodore, translated by Henry B. Cornwall, 1875, Plattner's Manual of Qualitative and Quantitative Analysis with the Blowpipe. *
III. Microscopic Examination of Common Fungi
When
hunting for
interesting life-forms to study with the microscope, one's own
refrigerator can
be a productive search area. Bacteria, molds, and yeasts are present in
even
the best-kept refrigerators, but the most rewarding search is one
carried out
in a fridge that hasn't been cleaned in a couple of months.
This un-appetizing mold growth on a carrot gives us an abundant source of hyphae, conidiophores, etc. to study with the microscope. It appears the mold infestation started in a bruised or torn section in the side of the carrot. This brings to mind the invasion of damaged tissues by opportunistic fungi.Procedure: A search in the refrigerator turned up at least one piece of moldy produce: a carrot showing tufted masses of white and blue-green fungi. Samples of this were removed with forceps 5 and placed on a clean microscope slide; two or three drops of prepared hematoxylin stain were then added and allowed to soak into the mold samples. A clean cover slip was placed on the preparation and as many air bubbles as possible were pressed out gently. The slide was studied with an Observer III microscope and photographs were taken using a MiniVID USB eyepiece camera.
Results and Discussion: At 40x total magnification, the stained fungi showed up as tangled masses of thin stalks (hyphae), sometimes terminating in complex structures that warranted closer inspection. At 100x total magnification these structures became much clearer and were vaguely reminiscent of sea-anemone tentacles or squashed flowers. The first MiniVID photo was taken at 100x.
At 400x total magnification, individual spherical structures (conidia?) became visible; these are shown in the photographs below. The "flower-like" conidiophore was difficult to bring into focus, thanks partially to its high 3-dimensional relief as compared to the rest of the hyphae.
Though the
hematoxylin
stain was chosen arbitrarily (without researching what the best stain
would
have been), it adhered well. A proper procedure would have included de-staining
to remove excess pigment, but we obtained passable results for this
mini-experiment. We initially guessed that the fungus samples from the
carrot
represented a common member or members of the genus Penicillium,
or
perhaps Cladosporium. Since no photo-atlas of fungi was handy,
some
meandering on the web turned up the very informative
doctorfungus.org
website. The site
contains an impressive, searchable
image
bank. Of the photos we
searched, the closest match was Penicillium chrysogenum, a
common fungus
in many households-- and the source of the antibiotic penicillin.
Though P.
chrysogenum may not be the true identity of our sample (any
mycologists out
there: feel free to make suggestions), one can easily notice the
"strings" of spherical phialides on the conidiophores in photos of
known P. chrysogenum and in the following photo of our
unidentified mold
sample 6:
See also Tom Volk's Fungus of the Month for November 2003. There's a nice phase-contrast photo of P. chrysogenum.The photomicrographs were taken with a Mini-VID eyepiece camera in an Observer III microscope. The sample was prepared minimally and handled with very little care, and the slide was only a temporary mount. Still, this mini-experiment brought to light some interesting objects which had been silently growing in the refrigerator. A more advanced experiment (and perhaps the subject of a future newsletter) would be to see if we can chemically detect one or more functional compounds (e.g., beta-lactams such as penicillin) in these household fungi.
IV. Site News
The
Belomo loupes
have
arrived back in stock after a long wait. The manufacturer has raised
the price,
but at $18.95 the Belomo is still definitely worth it. It also
seems
their quality control is even better than before. Hopefully we will
have these
loupes in stock for some time to come. More
laboratory
glassware will soon be available in the on-line catalog: micro-beakers,
micro conical flasks, another size of
petri dish
(65 mm),
and a larger size of glass retort
(1000 mL).
The micro glassware is popular with hobbyists and teachers who don't
wish to
use up large quantities of reagent when doing experiments. It seems the
trend
of chemistry (as a hobby, at least) has gone toward micro-chem in the
past
decade or so, which is not unwelcome for the mineral collector who has
only a
tiny shard of sample to spare when having a go at analysis. Besides,
some of
the more toxic reagents used in mineralogy, such as benzidine or
thioacetamide,
are best kept and used in the smallest quantities that are practical.We're
pleased to
announce the arrival of the new "Tachometer" and
"Select-speed" versions of the
Ultra 8
centrifuge.
The Ultra 8 "Select" model has four settings corresponding to
CLIA-recommended speeds for standard clinical centrifugation of body
fluids.
The Ultra 8 "Tachometer" model has variable speed and a built-in
tachometer with digital readout-- useful for protein purifications and
any
other experiment where it's important to know and control the exact
relative
centrifugal force (RCF). If you have an original Ultra 8V or other
centrifuge
without built-in speed indicator, we now also sell a hand-held
tachometer.Minerals...
we've still
got minerals, and plenty of new ones that are yet to be uploaded to the
site.
The mineral
cabochons
section has been expanded, and we've added some
custom-made
jewelry
that focuses on exotic mineral cabochons. An exotic mineral cabochon
fashioned
into a piece of jewelry is beautiful and rare, and it's also quite a
conversation starter. Why not have a little science in your jewelry,
and a
little jewelry with your science!
That concludes this issue of the CR-Scientific newsletter.
Until next time, stay safe and have fun.
Notes:
1 "Simply" boiling, indeed. Some sulfuric acid molecules will escape the surface of the hot liquid into the air, even when the acid is not at a rolling boil-- hence the caution to do this outside. There's something called vapor pressure, which means a liquid will give off appreciable vapors even when it's not quite boiling. As the concentration of sulfuric acid versus water becomes higher and higher, more sulfuric acid vapor escapes. The temperature will of course climb, but a "rolling boil" is not necessary to allow dangerous acid vapors to go into the air.
Back to article
2 Another reminder, in case you forgot... NEVER breathe acid vapors. They will cause irreparable lung damage and possible death.
Back to article
3 Some sources list this as 337° C. Again, no one seems to agree on something so simple as "boiling points", but that's because we're not dealing with something so simple as "pure water at 760 mm Hg". The best that one can usually do is to request the boiling point, concentration, and specific gravity of a particular lot of sulfuric acid when buying it from a chemical supply house. Also: It is difficult to prepare anhydrous sulfuric acid, but it's also unnecessary for the majority of applications.
Back to article
4 Ed. note - a hot test-tube may retain enough heat that the liquid in it will still boil briefly after it's removed from the flame, especially if a "boiling chip" is present. This after-effect usually doesn't last more than a couple of seconds.
Back to article
5 Tearing off pieces of the fungus probably filled the air with spores. Now they're really everywhere. The writer probably inhaled some of them, which is likely not desirable.
Back to article
6 As you can see, the conidiophores, phialides, etc. are tangled and mashed all over the place in our samples, causing them not to look like the nice and neat reference photos with which we're comparing them. Also, there are so many genera and species of fungi that it might be a little naïve for us to think we've pegged the identity this easily. It has been an enjoyable try, though.
Back to article
While the information in this newsletter is thought to be accurate to the best of the authors' current knowledge, it is not guaranteed to be free of errors or to be suitable for any particular use. The procedures and experiments outlined within can be dangerous or even fatal if carried out improperly. If you choose to attempt any of them, you proceed entirely at your own risk.
Contents of his newsletter are copyright of CR-Scientific, 2004. You may distribute this newsletter freely provided the contents of the file are not truncated or altered in any way. Please email us if you find any errors or omissions or would simply like to make a suggestion.
The "Qualitative Analysis of Hemimorphite" article is copyright of Mr. Dana Morong, 2003-2004, and may not be copied or distributed without his prior written permission.
General Terms of Use for this website
Newsletter Index Page
Lab Glassware
Main Page