Home > Daynotes Home > Week of 25 August 2008

Photograph of Robert Bruce Thompson
Daynotes Journal

Week of 25 August 2008


Latest Update: Friday, 29 August 2008 11:26 -0500

Paying for this Place
Visit Barbara's Journal Page

Monday, 25 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

08:50 - 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.



When 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.

Sometimes, 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 volumetric flask.

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.

Primitive 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 is reached.

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.

For 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.


[top]

Tuesday, 26 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

09:11 - 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?



I've 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.

Beginning 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.

Now, I 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 advanced electives.

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.


[top]

Wednesday, 27 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

07:54 - 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 tomorrow.

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.



I 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.

Most 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.

So 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.

When 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.

So I 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)"

So, 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

Right 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 standardized.

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.


[top]

Thursday, 28 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

08:54 - 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.

I 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.

I 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 hundred years.



[top]

Friday, 29 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

07:54 - 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.

Wagner's 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 caffeine concentration. 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:

"Wagner's 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 C8H10N4O2HII4, is obtained."

Guess 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.

This 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.

As for "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.



09:47 - 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.



11:26 - 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.

I'll 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.


[top]

Saturday, 30 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

00:00 -



[top]

Sunday, 31 August 2008
[Daynotes Forums]    [Last Week]   [Mon]  [Tue]  [Wed]  [Thu]  [Fri]  [Sat]  [Sun]   [Next Week]    [HardwareGuys Forums]

00:00 -



[top]

Copyright 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 by Robert Bruce Thompson. All Rights Reserved.