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Week of 20 April 2009


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Monday, 20 April 2009
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07:35 - Whenever Barbara buys a new mechanical device, I name it after a supercar. So, when she bought her lawn vacuum, it became her Lawn Lamborghini, her new vacuum cleaner became her Floor Ferrari, and so on. So, when she bought a new four-slice toaster at Costco last weekend, it became ... wait for it ... her Tosteressa. Argh. Argh. Argh. Sometimes I disgust even myself. Barbara just rolled her eyes.


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Tuesday, 21 April 2009
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08:57 - I just finished writing up the final lab session in the twelfth and final issue of the HomeChemLab.com subscriber newsletter. That lab session was originally going to be about potentiometric titration, but I ended up dropping that idea and going with something entirely different.

A week or so ago, I was reading a news item on CNN or Fox about environmental toxins released by reprocessing old computers, televisions, and so on. That started me on a journey to various pages about such toxins, and I eventually ended up reading about lead-testing kits for homeowners. There are a lot of those kits out there, but from what I read it seems that most or all of them are not actually very useful. The packaged testing kits generally produce lots of false positives and/or false negatives. I'm not sure which is worse.

So, given that most homes built before about 1977 have lead-based paint present, I decided to see what I could do with the resources of a home lab to do real lead testing, ideally at least semi-quantitative. The result is Laboratory 19.8: Analysis of Paint Samples for Lead.


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Wednesday, 22 April 2009
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08:52 - Lab day today. I need to make up the chromate and iodide lead-test reagents and a standard lead solution, do a serial dilution of the standard lead reagent, and test the precipitation behavior of lead chromate and lead iodide. I know the Ksp values for those salts, of course, but knowing what's supposed to happen and seeing what actually happens are two different things.

I'm also thinking about doing some lab work aimed at detecting so-called "heavy metals", not all of which are heavy and not all of which are metals. I mean, most such lists of "heavy metals" include aluminum and beryllium (which are light metals), arsenic (which is a metalloid), and selenium (which is a non-metal). Some have argued to replace the meaningless term "heavy metals" with an awkward phrase such as "elements that have no biological role", but even that's wrong. Some elements, such as selenium and nickel, are essential to life in trace amounts, but are extremely toxic in amounts beyond traces. Other elements are essential trace elements in one oxidation state, such as chromium(III), but lethal toxins in other oxidation states, such as chromium(VI).

I have specimens of most of the ion species I'm interested in, including antimony, arsenic, barium, lead, mercury, vanadium, and so on. I don't have any osmium or thallium or any of the radioactives, but those are so rarely encountered that I won't worry about them. The one notable gap in my collection is cadmium, which I intentionally avoided when I was stocking my lab because I didn't foresee a need for it and there's no point to keeping hazardous chemicals around if one doesn't intend to use them. So I guess I'll order a few grams of cadmium oxide, which is the least hazardous of the common cadmium compounds. I can convert it as needed to the chloride, nitrate, or sulfate simply by reacting a small specimen with one of the mineral acids.


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Thursday, 23 April 2009
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08:45 - I made up the lead-test reagents yesterday and did a quick sanity-check test by doing serial dilutions of the 50,000 ppm standard lead stock solution to about 25,000, 12,500, 6,250, 3,125, and 1,563 ppm and then testing them with iodide and chromate reagents. In each case, an easily-visible precipitate occurred as soon as I added a couple drops of the reagent. Today or tomorrow, I'll extend the serial dilution from six wells to 12 wells, which takes me down to about 24 ppm.

The current standard for "lead-free" paints is maximum lead content of 600 ppm (0.06%). Assuming a 1 g paint chip sample, 3 g of extraction solution, and 50% extraction efficiency, if the paint chip contains the full 600 ppm lead, I should get an extract solution that contains lead ions at about 100 ppm. Of course, that 50% figure is a pure guess. The actual extraction efficiency could be anything from 0% to 100%, and could vary significantly with original lead concentration, makeup of the paint, and so on. I'm using 50% based on the literature.

My real problem at this point is the lack of known lead-paint samples to test against. Before about 1940, lead-based paint was extremely common, used in essentially 100% of all homes. That usage gradually declined over the next four decades. By 1977, when the government banned lead-based paint for residential use, perhaps 15% to 20% of all new homes were originally painted with some or all lead-based paint. In 1969, when our home was built, that figure was probably around 25% to 30%.

Interestingly, as the use of lead-based paint declined its use also apparently skewed toward less expensive homes, apartments, and the like. More expensive single-family homes tended more and more to be painted with non-lead paints, mostly based on titanium dioxide, which was more expensive than lead carbonate at the time. So, the upshot is that the 25% to 30% overall likelihood that lead-based paint was used for new residential painting in 1969 has to be reduced by some factor because this was a mid-range single-family home. So call it a 12% to 15% overall likelihood that any lead-based paint was used originally in our home.

But most homes built in that era used a mix of lead-based and non-lead paints, with lead-based paints most likely to be used for exterior painting. And the only accessible original paint in our home is in the attic stairwell, so I have to reduce the likelihood further. At a guess, there's maybe a 5% chance that that stairwell paint is lead-based. I'll take a sample and test it to find out.



15:26 - One of the phony arguments frequently tossed around by anti-science religious nutters is the supposed absence of transitional forms in the fossil record. In fact, we have plenty of transitional fossils, with more being found regularly. Here's another one, a proto-seal with feet rather than flippers.

What's astounding to anyone who understands anything about the fossilization process is not how few fossils of any sort are found, but how many. Our bodies, and those of other animals and plants, are quite fragile, particularly over geologic time periods. Over millions, tens of millions, and hundreds of millions of years, things change, including things we consider unchanging from our short-lived perspective. Mighty rivers appear and disappear. Lush forests become deserts, and vice versa. The seabed is lifted to form mountain ranges, which are subsequently eroded. Even the continents themselves drift. Why, then, would anyone expect traces of anything as fragile as plants and animals to remain?

Despite that, fossils representing newly-discovered extinct species continue to be found regularly. Quite often, an extinct species is known only from a single fossil example. The wonder is that scientists found even that one surviving example. I'm not an evolutionary biologist, but I'd guess that 99+% of the extinct species that have ever existed are not represented by even a single fossil example. And yet the religious nutters would have us believe that every species that ever lived should be found in the fossil record, and the fact that they are not somehow disproves evolution. What a bunch of maroons.


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Friday, 24 April 2009
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08:24 - I have some more lab work to do today, not least including a general cleanup. I have dirty (well-rinsed but not washed) glassware overflowing the sink onto the counters on both sides of it. I'm running out of counter space. Time for a general cleanup.

Sometime in the next couple of weeks or so I want to shoot a video of the lead-detection lab. I'm going to see if Mary Chervenak is available to do the on-camera stuff.



11:02 - The things I learn while doing other things. I just did a serial dilution of my standard 50,000 ppm Pb2+ solution. I started by using a pipette to transfer 10.0 mL of distilled water to each of 11 test tubes. I then transferred 10.0 mL of the 50,000 ppm lead solution to the first test tube, giving a 25,000 ppm solution. After agitating to mix the solution, I transferred 10.0 mL of the 25,000 ppm lead solution from the first test tube to the second, giving a 12,500 ppm solution. I continued this procedure until I reached the 11th test tube, which ended up with a solution that's about 24 ppm with respect to lead ion. (50,000 ppm / 2,048 = 24.4+ ppm).

As I made each dilution, I transferred one drop of the solution to a labeled spot on a piece of ordinary copy paper. The goal is to have a series of 12 spots, each half the concentration of the preceding spot, to test with sodium sulfide reagent to determine the threshold sensitivity of the sulfide reagent. When I put a drop of the 50,000 ppm solution on the paper, the drop just sat there, not spreading at all. I thought that was a bit odd, but didn't think much more about it until I'd done several more spots.

When I completed spotting the 12 concentrations on the paper, I noticed that the lead concentration determines the behavior of the spot. None of the first six spots (50,000, 25,000, 12,500, 6,250, 3,125, and 1,563 ppm) have spread at all, even after an hour. They're just sitting there as beads of solution on top of the paper surface. The 791 ppm spot has spread a tiny amount past the edge of the drop, perhaps 0.25 mm. The 391 ppm spot has spread a bit more, and the last four spots (195, 98, 49, and 24 ppm) have spread completely and soaked into the paper.

That's actually annoying, because what I wanted was a series of spots of nearly identical size but different lead concentrations. As it turns out, the most concentrated spots will end up perhaps 4 mm in diameter, while the least concentrated spots will end up being four to five times that diameter, spreading the lead present in them over 16 to 25 times the surface area.


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Saturday, 25 April 2009
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08:40 - In a moment of insanity last night, I decided to do a version upgrade on my den system from Ubuntu 8.10 to Ubuntu 9.04. I say insanity because the den system has been unstable lately. It's probably a power supply problem, but it may be memory. At any rate, I started the version upgrade, which wanted to download about 1,200 files. The download was slow, probably because the Ubuntu servers are still being hammered. About half an hour into the download, the system rebooted. I restarted the version upgrade, which took up from where it had left off, and went to bed.

This morning, I found the system had rebooted again. I logged in, and restarted the version upgrade. It started at about 800 of 1,200 files downloaded, and finished up the download within a few minutes. Then it started installing and configuring the version upgrade, which originally said it would take about an hour. About 10 minutes into that process, it was showing 19 minutes left to go when the system rebooted spontaneously again. Unfortunately, it's completed borked at this point, with the new version half-installed. Oh, well. I needed to tear down this system and replace the power supply anyway. I haven't lost any data.



12:00 - Every time I clean up my lab, I think how lucky my friend Paul Jones is to be a chemistry professor. He has grad students and lab assistants to do the scut work like washing up, mixing bench solutions, and so on. I have to do all that stuff myself.

I just spent a couple hours cleaning up, mostly washing glassware. Scores of dirty beakers, flasks, test tubes, graduated cylinders, and so on. Well, not actually dirty. In fact, just looking at most of them, you'd think they were already clean. I rinse stuff pretty thoroughly before I set it aside to wash up in batches. The wash up procedure differs a bit from ordinary dish washing. It starts the same way, with a wash in sudsy water and a tap water rinse and drain.

Our tap water is so soft that that'd probably suffice for most purposes, but after the first drain I rinse again, this time with distilled water, and drain again, followed by yet another rinse with distilled water, drying the exterior with a clean towel, and putting the glassware away. Sometimes there are water droplets left inside narrow bore things like graduated cylinders and test tubes, but I don't worry about that. It's only distilled water and it'll evaporate eventually. If I need the stuff dry, I'll do a final rinse with acetone and, if necessary, use canned air to blow it out.

That's the procedure to get glassware ordinarily clean. If it needs to be extraordinary clean, I wash the stuff, rinse in tap water and then swirl a concentrated solution of sodium hydroxide in ethanol around the inside of the glassware. That dissolves just about anything, including the glass itself if it remains in contact too long. Then I rinse in distilled water and drain, repeat the distilled water rinse and drain.


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Sunday, 26 April 2009
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08:58 - There was a very disturbing article in our newspaper this morning, about a man who's spent 20 years in prison for molesting his daughter, who was then 10 years old. There was no physical evidence. He was convicted solely on the testimony of a 10-year-old child. Worse, the girl recanted immediately after the conviction and has been telling everyone ever since that she lied. All of the evidence, such as it is, points to this man's innocence. On the face of it, there is and always has been reasonable doubt, to put it politely.


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Copyright 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 by Robert Bruce Thompson. All Rights Reserved.