Week of 10 December 2007
Update: Friday, 14 December 2007 08:38 -0500
I spent some time this weekend working on the chem lab book, but I also
devoted some time to expanding the outline for the home forensics lab
book. I added one lab session on using presumptive tests for alkaloids.
One of the tests uses a solution of potassium iodide and bismuth
nitrate in acetic acid, called Dragendorff Reagent. How cool is that?
of the neat things about forensic chemistry is that most of the "wet
chemistry" tests originated in the 19th century and are therefore
pretty easy to reproduce in a home lab. And, despite the proliferation
of expensive instrumental methodologies like gas chromatography, atomic
absorption spectrophotometry, and neutron-activation analysis, wet
chemistry methods are still important, not least for presumptive tests.
of these instruments are extremely expensive and in short supply. The
flood of requests for forensics tests means that only a tiny percentage
of them can be completed with the expensive instruments, so presumptive
tests are important as initial screening tests. If presumptive tests
turn out negative, there's no point to doing the expensive,
time-consuming instrumental tests.
And presumptive tests can be
pretty reliable, although it's often necessary to use two or more
presumptive tests to increase certainty. For example, a sample that is
suspected to be an illegal drug might be tested with presumptive test
A, which yields a specific color change if the suspected drug is
present. If the color of the test solution changes appropriately, the
investigator has a reasonable suspicion that that drug is present in
the sample. But it's not guaranteed, because nearly all presumptive
tests are subject to false positives, which occur when a completely
different (and probably legal) substance causes the same color change.
the next step is to run presumptive test B against the sample. The B
test uses different chemistry than the A test, so a positive test with
both A and B greatly increases the likelihood that the suspected
substance is in fact present. Although the B test is also subject to
false positives, the probability that a particular legal substance
would cause a false positive with both tests is quite small. If there's
any doubt after running A and B, the technician can run presumptive
test C for confirmation.
Only when the technician is satisfied
that the substance is almost certainly the suspected illegal drug is
the sample sent to the forensics laboratory for confirmatory testing
with the expensive equipment. That expensive equipment has one other
advantage. Presumptive tests are, almost exclusively, qualitative or at
best semi-quantitative rather than quantitative. Presumptive tests may
tell you that a suspect drug or poison is likely to be present in a
sample, but they can't tell you how much is present, at least not with
a high degree of accuracy. Because quantities are important
evidence in drug trials, the results of the instrumental methods are
invariably used in the actual trials.
Wet chemistry methods are
also important for gathering evidence in the field. Things like testing
for blood traces with luminol or fluorescein, revealing latent
fingerprints with ninhydrin, iodine fuming, SPR (small particle
reagent, AKA molybdenum disulfide), silver nitrate, or super glue, and
so on. And some of the wet chemistry methods that are doable in a home
lab are quite sophisticated, for example using electrophoresis to
separate DNA samples.
This is going to be a dynamite book. I just hope O'Reilly will go for it. If not, I may publish it myself.
Tuesday, 11 December 2007
- I just got back a whole bunch of home chem lab chapters from my editor, so guess what I'll be doing all day today.
Wednesday, 12 December 2007
I blasted through final edits on eight chapters yesterday. Today, I'll
incorporate the final edits on chapter 20, Quantitative Analysis, and
chapter 21, Synthesis of Useful Compounds. I haven't gotten my editor's
final comments on Chapter 22, Forensic Chemistry, but I'll get those
done as soon as he sends them to me.
After I complete the edits,
I'll be spending several days in the lab, doing setups and shooting
images. I think I'll move a PC down there temporarily. It'll take up a
lot of bench space, but it'll save a ton of running up and down the
stairs. I need to have the text of the chapters readily available while
I'm doing the setups and shooting the images, and it'll be useful to be
able to edit the text immediately while I'm shooting the images. Or I
may just carry my notebook downstairs.
Mary and Paul are coming
over this weekend for dinner and to do a lab inspection. I doubt it'll
ever happen, but if the feds do kick down my door one day and bust
me for unauthorized possession of a chemistry lab, it'll be useful to
have two independent expert witnesses who can testify that my lab is
for the purpose of writing science books rather than making illegal
drugs or explosives.
I finished up the edits on all of the chapters I have, so it's time to
get the lab cleaned up a bit and set up to shoot a whole bunch of
images. I decided to carry my antique Compaq Armada E350 notebook down
to the lab so that I could read along in the text as I set up images to
shoot. That notebook has only a Pentium III/750 processor and, IIRC,
512 MB of RAM. It has Xandros installed, so I'll need to do something
about that. (Since Xandros signed a patent pact with Microsoft, I've
refused to have anything to do with Xandros.)
thought about installing a low-footprint Linux distro on the notebook,
but instead I decided to give Linux Mint a try. I'm downloading it now
from a torrent, so we'll see how it works. The torrent is unusually
fast. It's running about 600 KB/s sustained, which is about the limit
of my broadband connection.
Thursday, 13 December
I got chapter 22, Forensic Chemistry, back from my editor last night
and finished the updates on it this morning. Today is a lab day.
it turned out, I wasn't able to load Linux Mint or Ubuntu 7.10 on my
antique notebook. Not surprising, considering the thing has only 256 MB
of memory rather than the 512 MB I thought it had. I also found out
that the notebook currently dual-boots an old version of Xandros and
Windows 2000, so I'll probably just leave it as is for the time being.
It's good enough for what I need to do in the lab. It has an 802.11g
Wi-Fi card in it and one USB port, which is all I really need for
- Here's a politically-incorrect article I was surprised to see, even on FoxNews.com: Dogs Save Australia Boy, 2, From Drowning
The two canine heroes pulled a drowning 2-year-old boy from a dam pond
and dragged him up the bank to safety. One of the dogs was a Rottweiler
mix and the other a Staffordshire terrier (one of the breeds commonly
called pit bulls), two of the breeds most feared by people who
don't know any better.
In reality, of course, pit bulls are one of the breeds least
likely to attack humans, having had aggressiveness toward humans bred
out of them for many generations. Pit bulls were originally bred not
for dog fighting, but for bull- and bear-baiting. The dogs were often
badly injured in the pit, and the safety of their handlers depended on
the dogs being completely unaggressive toward people under all
circumstances, including when the dogs were badly injured. Anyone who
has experience with pit bulls (other than puppy-mill dogs, which are
dangerous regardless of the breed) knows that pit bulls are playful, gentle, and
spent yesterday afternoon in the lab, getting things cleaned up and
organized a bit. More of the same today. I need to reserve some counter
space temporarily for doing setups and shooting images.
found out why the notebook computer wouldn't load Linux Mint 4.0 or
Ubuntu 7.10. It has not the 512 MB of RAM I thought it had, nor even
256 MB, but only 128 MB. Crucial no longer has this model listed on its
configurator, but I see that a pair of 256 MB SDRAM PC133 SODIMMs for a
similar model costs over $100. No, thanks. I'll just retire this system
to the lab long enough to get done what I need to get done. Then it
goes back in astronomy kit for use as a field notebook, for which it's
Saturday, 15 December
1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 by Robert Bruce