Week of 25 August 2008
Update: Friday, 29 August 2008 11:26 -0500
Barbara and I watched series three of Weeds over the weekend, and
agreed that the whole series deserves a 7/10 rating. That compares
pretty favorably with the best of the series we've watched. We give
series like Jericho an 8/10, and series like Upstairs,
Downstairs; I, Clavdivs; Buffy The Vampire Slayer; Firefly; and
Veronica Mars a 9/10.
I'm writing up lab sessions for the forensics book, I often run
downstairs to the lab to do a quick-and-dirty run-through, just to make
sure that things work the way they're supposed to. Later, after the lab
is completely written up, I actually do the lab session step-by-step.
I re-write the lab session based on what I observe in the quick
run-through. That's what happened with the lab session on doing a
quantitative analysis of an alkaloid with Wagner Reagent (which is a
solution of iodine and potassium iodide, basically tincture of iodine).
Wagner Reagent reacts with most alkaloids to yield an insoluble
precipitate. My intention was to use excess Wagner Reagent and then
back titrate with thiosulphate or vitamin C to reduce the excess brown
iodine to colorless iodide ions.
The problem turns out to be
that the precipitate is (a) brown and (b) nearly colloidal. In other
words, the precipitate gives the liquid pretty much the same color as
iodine does, and it remains suspended in solution for quite a while,
instead of settling quickly to the bottom of the vessel as a
well-behaved precipitate should. Hmmm.
I've been on a
non-fiction kick lately. Instead of reading mysteries in the evenings,
I've been reading various books on the history of chemistry. The other
night, I was reading Aaron J. Ihde's The Development of Modern Chemistry,
which was published in 1964, the same year I got my first big chemistry
set. In the chapter on the development of analytical chemistry, there's
a section on Karl Friedrich Mohr, a German chemist and pharmacist who
is probably best-remembered today for his synthesis of Mohr's salt
(ferrous ammonium sulfate) and for devising various types of analytical
glassware, including the Mohr burette, the Mohr pipette, and the
Interestingly, analytical chemstry really
didn't take off until about 1860, when volumetric techniques became
established largely due to the efforts of Mohr to design more accurate
volumetric glassware. Until then, chemists depended mostly on
gravimetric techniques (weighing precipitates and so on). Volumetric
(titrimetric) techiques were largely relegated to industrial processes,
metallurgy, and other endeavors that chemists regarded as pretty much
unscientific. And the chemists had a point. There wasn't much in the
way of accurate volumetric glassware available, and the indicators that
would later be used to establish accurate endpoints for titrations
weren't yet available. Endpoints were often determined by such
techniques as watching for (or listening for) bubbling to cease.
burettes had been available since the first decade of the 19th century,
but they used ground-glass stopcocks that leaked and jammed. Mohr
introduced an improved burette that used a short piece of rubber tubing
with a pinchcock, thereby allowing delivery of accurately
measurable volumes of titrant.
Mohr also devised some improved
titration techniques. One of them was related to silver nitrate
titration of halide (chloride, bromide, or iodide) ions, which was an
important analytical technique at the time. When silver nitrate
solution is added to a solution that contains halide ions, insoluble
silver halide precipitates. The problem is, the fine, flocculent
precipitate of silver halide remains suspended for a long time in the
titration vessel, making it impossible to determine when the endpoint
Well, not impossible, as long as you were really,
really patient. Before Mohr's improvement, the standard techique for
this titration was to add a drop of silver nitrate titrant, wait for
the precipitate to settle, and another drop, wait again, and so on. One
titration could take literally all day long, if not several days. The
gravimetric alternative was clearly superior: add sufficient silver
nitrate to the aliquot of halide ion that you were sure silver nitrate
was in excess. Filter the silver halide precipitate, wash it, dry it,
and weigh it. That took quite a while, but not the hours to days
required for the volumetric alternative.
Mohr's improvement to
titrimetric analysis of halide ion by silver nitrate consisted of
adding potassium chromate to the halide aliquot. Potassium chromate is
bright yellow, and provides an endpoint indicator. As long as excess
halide ions remain in the titration vessel, adding silver nitrate
precipitates them as light-colored silver halide, leaving the potassium
chromate unaffected and the liquid in the titration vessel bright
yellow. When all of the halide ions have reacted with silver ions, the
silver ions begin reacting with chromate ions, forming brick-red silver
chromate. The liquid in the titration vessel quickly changes from the
pure yellow color of chromate to a distinct orange, indicating the
endpoint of the titration.
With Mohr's method, there's no need
to allow the precipitate to settle, so an analysis of halide ion could
be completed titrimetrically in minutes rather than hours or days. I
actually used Mohr's method in one of the lab sessions in Illustrated Guide to Home Chemistry Experiments. At the time, I didn't know that Mohr had devised it, or I would have credited him.
the lab session on quantitative determination of an alkaloid by
iodometric titration, I have the same problem with a precipitate that
wants to remain suspended, so I'm going to use a similar method.
Originally, I'd planned to use an aliquot of Wagner's Reagent in the
titration vessel and use the alkaloid solution as the titrant. Instead,
I'll use an aliquot of the alkaloid solution in the titration vessel
and titrate with the iodine/iodide solution. I'll use a mL or two of
starch solution in the titration vessel to serve as an indicator.
Starch forms an intense blue-black complex with free iodine. Literally
one drop of excess iodine will turn the liquid in the titration vessel
from the brownish color of the precipitate to an intense blue-black.
So, with starch as an indicator, I can titrate quickly without waiting
for the precipitate to settle.
I don't watch TV and I don't pay much attention to the "news", so I was
surprised to learn that the olympics thing is over and the democrats
have started their convention. Both, coincidentally, are quadrennial
events, and both would be much improved by scheduling them once every
hundred years, or even every thousand. I can't imagine that many people
wasted much time watching the olympics, and I can't imagine that many
more will waste much time watching the democrats. Or the republicans.
Or have they already had theirs?
been spending a lot of time in the lab lately, and it's nice. I'm
alternating doing stuff with writing about doing stuff. I've also been
reading books about the history of chemistry for the last week or so,
and reflecting about how things come in and out of vogue. Until 1870 or
so, college chemistry courses were largely lecture-based, with
most students getting very little lab time. The best professors, men
like Liebig, Wohler, and Hoffmann, exposed their best students to a
significant amount of lab work, but they were the exceptions and they
focused their efforts only on the best of the best students.
with Frankland, things started to change. College chemistry courses
gradually became intensely lab-based. Frankland's standard for an eight
hour teaching day was one hour of lecture and seven hours of lab. By
the turn of the century, these "practical" chemistry courses had become
the norm in most universities. Students spent, if not 7/8 of their time
in lab, at least significant time every day.
Now we've about
come full circle again. Talking with my friend Paul Jones, who's an
organic chemistry professor at Wake Forest University, I was stunned to
learn how little time students are spending in lab nowadays. From what
Paul said, it sounds to me as though today's students are getting about
one year's worth of lab work in a full four-year program.
know there's a lot more theory to be covered than there used to be, and
I know lab facilities and supplies are expensive, but it seems to me
that the pendulum has swung too far in the wrong direction. To my
perhaps obsolete way of thinking, chemistry students should actually be
doing chemistry rather than just reading about it and listening to
lectures about it.
If I were
teaching college chemistry majors, I'd want to be doing it in
a lab rather than in a lecture room. I'd want to teach general
chemistry to first-semester freshmen for four hours a day, five days a
week. I'd want to teach introductory inorganic chemistry to
second-semester freshmen for four hours a day, five days a week. I'd
want to teach introductory analytical chemistry to first-semester
sophomores for four hours a day, five days a week, and introductory
organic chemistry to second-semester sophomores for four hours a
day five days a week. Junior year, I'd do the same with physical
chemistry and biochemistry, and senior year would be allocated to
At the end of a four-year course, these kids
would know quite a bit about chemistry. They'd have spent fully half of
their time in courses directly related to their major and they'd be
well prepared for graduate school in their preferred area of chemistry.
Of the remaining half their time, they'd have spent most of it on
related courses, things like mathematics, logic,
biology, physics, engineering, the history of science, and so
on. That would leave no time for the crap that colleges now require,
and that's all to the good. College science majors shouldn't be wasting
time on non-rigorous stuff like history and literature. That's
something you read about in your spare time, not something that has any
place in college.
Wednesday, 27 August 2008
Things have been very dry around here, but we got some relief yesterday
and overnight. The last time we walked the dogs, we'd had about 3/4" (2
cm) of rain. Overnight, we got an additional 3.5" (9 cm), with another
1" to 2" (2.5 cm to 5 cm) expected today and more overnight and
The rain has been very widespread, so there should be
at least some improvement in the flow rates of the rivers and the
levels of the reservoirs, which were already in reasonably good shape
for this time of year. We've been on the boundary of the extreme
drought and exceptional drought areas. The rain we've gotten won't
eliminate the drought, at least in terms of the water table level, but
in terms of ground moisture and reservoir levels, it should get us back
to something approaching normal.
spent quite a bit of time in the lab yesterday working with
Dragendorff's Reagent, which is a general qualitative test for the
presence of alkaloids. There are many formulations for the reagent,
even Dragendorff himself used different ones, but all of them have in
common the presence of bismuth ions and iodide ions in acidic solution.
of the formulations call for bismuth subnitrate and potassium iodide in
acetic, hydrochloric, nitric, or sulfuric acid. Bismuth subnitrate is
obtainable, but few lab supply vendors carry it, at least those that
serve home scientists. So I decided to try an alternative. Pepto-Bismol
tablets contain 262 mg of bismuth subsalicylate, which in terms of
bismuth mass is equivalent to something like 211 mg of the subnitrate.
I put a couple of Pepto-Bismol tablets in a few mL of concentrated
hydrochloric acid in a medium test tube to see what would happen. They
started foaming, and the foam started climbing up the tube. When it got
near the top with no sign of slowing, I poured the contents into a
larger tube. The foaming continued, and the head continued to climb.
Eventually, I just poured the contents into a 150 mL beaker.
the foaming finally stopped, I diluted the contents with some water and
ended up with a milky solution. I allowed that to settle, and a lot of
the solid matter (probably binders and similar inactive ingredients in
the tablets) settled to the bottom. I decanted off the supernatant
fluid and added some potassium iodide dissolved in a few mL of water.
The solution immediately turned bright yellow-orange and a heavy
flocculent precipitate developed. That settled out, leaving me with a
clear yellow-brown supernatant liquid. I decanted that off into a
storage bottle labeled "Dragendorff's Reagent". I tested that reagent
against some tonic water, which contains the alkaloid quinine, and got
a positive test, a bright yellow solution from which eventually settled
a beautiful red-orange precipitate. Hmmm. It seems to work.
decided to make some "real" Dragendorff's Reagent. I dissolved about
0.4 g of bismuth subnitrate in concentrated hydrochloric acid. It
dissolved completely to form a clear, colorless solution. Then I added
some potassium iodide solution and ended up with a clear, bright golden
yellow solution, with no precipitate. I tested that against tonic
water, and got the expected positive reaction. I poured that solution
into another storage bottle labeled "Dragendorff's Reagent (real)"
both formulations appear to work. The stuff I made up with Pepto-Bismol
is a clear yellow-brown solution versus the golden yellow of the real
stuff. I talked to Paul Jones about possible reasons for the
differences, and decided that it'd be okay to present the alternative
formulation in the book, assuming that it also worked with some other
alkaloids. I'll test those today, and if both solutions give similar
results, I'll include both formulations in the book.
Here's something stupid: FDA to consider rules for food allergy warnings
now, food producers are required to label products that intentionally
contain such allergens as peanuts and dairy products, but labeling of
products that may unintentionally contain such allergens is voluntary.
The government is thinking about making that labeling mandatory and
Think about that for a moment. If I'm a food
producer, I'm going to slap a warning about every potential allergen on every
container of every product I make. Hell, if I sell bottled spring
water, I slap a warning on it: "May contain peanuts, dairy products,
..." What's the downside? It's true. My products could, somehow, be
contaminated with such allergens. It may be extremely unlikely, but the
unlikely sometimes happens. If I've labeled my products as such, I'm
covered. If I haven't labeled them, I can be sued.
So why would
any food producer not label all of its products as potentially
containing such allergens? Is the government going to tell me that I
can't put warning labels on my products because the likelihood of
contamination is too small? Fine. If so, I want an ironclad guarantee
from the government that it'll cover my costs if I'm sued. If they push
me too hard, I may intentionally contaminate my products with
allergens. "Acme Spring Water: Now with Peanuts Added!" Is the
government going to tell me I can't use peanuts or dairy products in
the foods I sell? I don't think so.
Most of us will simply
ignore such warnings, because we don't have food allergies. The people
who do have food allergies will be worse off, because every product
will be labeled as unsafe for them, including those that have only the
tiniest likelihood of being contaminated.
The answer here isn't
more regulation. The answer is to continue voluntary labeling on a
reasonable basis, and to grant food manufacturers immunity from
lawsuits filed by people with food allergies who consume food products
that accidentally contained allergens but were not labeled as such.
Over the last week or so, I've read half a dozen books about the
history of chemistry. They make fascinating reading, almost like a
first-class mystery, watching very smart people starting from nothing
and figuring things out.
Most people assume, probably because of
the similarity in names, that chemistry evolved from alchemy. In fact,
alchemy was nothing but a sideshow, full of woo-woo and mystical crap
and intentionally obfuscated literature but utterly devoid of anything
that we'd consider real science. Alchemy arose among the ancient
Egyptians and Greeks and was practiced for the next 2,000 years, but it
contributed almost nothing to the base of human knowledge. Alchemists
were too busy trying to convert base metals into gold and looking for
the Philosopher's Stone to accomplish anything useful. All of the real
knowledge developed by alchemists over thousands of years could be
summarized in a small pamphlet, literally.
The real precursor of
modern chemistry was the knowledge base developed by artisans and
technicians, those who engaged in practical efforts to produce useful
products from raw materials. Distillers, dyers, tanners, physicians,
glass and ceramic makers, perfumers and cosmetics makers, miners,
jewelers, metal workers, and others engaged in similar practical
work made the important early discoveries and mastered most of the
processes such as distillation, calcination, crystallization,
cupellation, and so on that are normally credited to the alchemists.
looked at translations of two books that were published at about the
same time. One was an alchemy book, which was utter and complete
gibberish. (In fact, I think that word probably comes from the name of
the famous alchemist Geber.) The other was Agricola's De Re Metallica
(On Things Metallic), which was a practical handbook that summarized
the then-current knowledge about metals, everything from mining them to
smelting and purifying them to working them to dealing with fire damp
and flooding in mines. That book reads almost like a modern text.
was surprised when I read about the state-of-the-art in the sixteenth
century. They had no access to the reagents and most of the equipment
we use today, but they were able to assay ores accurately and
do similar quantitative procedures with high accuracy. I was
stunned when I read about the resolution of the best balances available
around 1500. Believe it or not, they were able to determine masses
accurate to about 100 micrograms. That's 0.0001 g, which is what a
$1,000 lab balance does today. Of course, they didn't use grams,
because the metric system wouldn't be invented for another two or three
I just wasted a couple of days by writing up a complete lab session
that I had to scrap and start over. The session was Laboratory 13.5:
Quantitative Analysis of an Alkaloid with Wagner's Reagent, which will
still appear in the book, but not in its original form.
Reagent (a solution of potassium iodide and iodine, basically the same
as tincture of iodine) reacts with alkaloids to form a brown
precipitate. Originally, I planned to use caffeine as the alkaloid.
Caffeine is common in soft drinks and hot beverages, which would give
readers many readily-available potential "unknowns" to analyze for
Better yet, most of these "unknowns" have established values that can
be looked up on the Internet. Mountain Dew, for example, contains about
15.5 mg/dL. And making a standardized caffeine solution is no problem,
even for someone without a balance. NoDoz and similar generic tablets
each contain 200 mg of caffeine.
So I wrote up the lab session
on that basis, doing all the calculations to get the concentrations and
aliquot sizes reasonable. After I finished writing up the lab session,
I went down to the lab to try it out. It doesn't work. Wagner's Reagent
does not precipitate caffeine. Wagner himself said that his reagent
would not precipitate caffeine. I knew that Wagner said his reagent
wouldn't precipitate caffeine, but I went ahead anyway on the basis of
an 1896 article by M. Gomberg (Jour. Amer. Chem. Soc., 1896, xviii., 331-342). The article begins:
statement that caffeine (and one or two other alkaloids) is not
precipitated by a solution of iodine in potassium iodide has hitherto
been accepted without question. The author shows that this is only true
of caffeine as a free alkaloid, and that when the addition of Wagner's
reagent is either followed or preceded by the addition of dilute
mineral acids, a dark-reddish precipitate, having the composition of C8H10N4O2·HI·I4, is obtained."
what? M. Gomberg was full of it. Wagner was right all along. Wagner's
Reagent does not precipitate caffeine, either as a free alkaloid or as
the hydrochloride salt. I know. I tried it. Repeatedly. I acidified the
hell out of the caffeine. I used a more concentrated solution of
Wagner's Reagent. Nothing I did would get the caffeine to precipitate.
Back to the drawing board, with a couple of days wasted.
time, I'm using quinine as the alkaloid, because I know it works. It's
a bit harder to get pure quinine for making up a standard
solution. Until a few years ago, 200 mg quinine sulfate capsules were
available OTC for treating nighttime leg cramps, but the FDA clamped
down on that. Nowadays, the FDA approves sale of quinine compounds only
by prescription and only for prophylaxis or treatment of malaria. It's
possible to order these capsules on-line from Mexican pharmacies, but
(a) that's illegal, and (b) you have to order $20 or $30 worth a time.
So I emailed my guy at Elemental Scientific to ask if he could make up
a standardized quinine sulfate solution in HCl for my readers. He's
agreed to do that, so I'm writing up the lab again on that basis.
"unknowns" the only real choice is tonic water. In the US, tonic water
is limited by law to containing no more than 83 mg/L of quinine base.
Presumably, Canada Dry, Schweppe's, and other tonic waters are at or
near this level, so that'll give me a reasonable ballpark for
calculating concentrations, aliquot sizes, and so on.
- Here's irony. FoxNews reports
that David Duchovny, who plays sex-addicted writer Hank Moody in the
Showtime series Californication, has been admitted to a rehab clinic to
be treated for, you guessed it, sex addiction. That makes me wonder
what really goes on behind the scenes in that program.
It's all over the news that McCain has chosen Alaska governor Sarah
Palin as his running mate. That gives major-party voters this November
an interesting choice. McCain-Palin, both of whom are notable for their
honor and integrity, versus Obama-Biden, both of whom are notable as
sleazy, radical-left machine politicians.
vote libertarian, of course, but for those who insist on voting
for one of the two major-party tickets, the choice seems pretty obvious
to me. The addition of Palin to the ticket is almost sufficient to
tempt me to vote Republican.
1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 by Robert