Re[2]: [at-l] UV pen

[tmcginnis@ucclan.state.in.us (Thomas McGinnis)]

     Just BTW, the kind of posting which you two (and others) have done on 
     this thread -- as demonstrated below -- is the kind of thread which 
     characterizes this list (the at-l) at its best. Direct, calm, 
     scientifically sound (or, well, making a very good effort, hell!) 
     deliberative, NOT vituperative, no avarice, just a sounding out of 
     ideas and evidence, guesses and findings. A tad of respect, a touch of 
     humor (and on a UV lightsource, that's a challenge).
     
     Thanks for setting a high caliber tone in your discussion. As a 
     (semi-retiring) water economist, I've appreciated where the thread has 
     gone, even if I haven't had time to join in.
     
     Oh so soberly,
     Sloetoe.


______________________________ Reply Separator _________________________________
Subject: Re: [at-l] UV pen
Author:  "David  F. Addleton" <dfa@wimlaw.com> at ima
Date:    7/28/99 3:10 PM


Jim,
     
I'm glad to have physicists and physicians on this list, since I'm neither, 
and definitely appreciate your input, critique, and etc. I *expect* to be 
wrong about some of this stuff, since my science education is limited to 
first level and a few second level college courses from the early 70s.
     
> > I will beg to differ from you on this. In my experience solar uv works 
> > quite well to purify water.
> > 
> This is the kind of unscientific statement I have a problem with.
     
Agreed that anecdote doesn't a peer-reviewable scientific statement make, 
since it comes without appropriate measurements and counts etc. But it 
remains *scientific* in a generic, empirical sense, since it arises from 
direct experience. If between two people all intake remains identical but 
the water source, and one of them gets sick, we don't have a large sample, 
but I'm willing to bet on the water source identified with the well person 
and to neglect the water source used by the guy who got sick.
     
> How can
> you say that solar uv works well without any testing? 
     
You're completely correct: I cannot make a statement regarding counts of 
the various pathological causes in water subjected to solar uv radiation 
before or after. I can empirically state, however, I and my family and 
friends did not get sick drinking from streams with the characteristics 
previously mentioned; that I have used solar radiation to make tea in glass 
jars and did not get sick subsequent to drinking it. And at some level we 
really don't care about the actual counts of pathogens from filters, 
iodine, boiling, or whatever, so long as the count is sufficiently low we 
don't get sick.
     
> Only a before and
> after test is valid (test for "bugs" and find them - radiate them - test 
and
> they're gone).
     
For peer-reviewed science I agree; for practical everyday empirical 
reasoning, I don't agree. The kings of old who used slaves to test their 
food and drink to assure it hadn't been poisoned, for example, conducted an 
empirical experiment each time they brought in the poor slave. The miner's 
canary served as an adequate meter for certain gases. Triangulating among 
three or four distant mountain peaks, leaving your landrover for a long 
hike into the mountains, and subsequently returning on camels days later, 
directly to the landrover's location, may not result in accurate geometric 
measurements, but it kept us from getting lost on our way back to the 
vehicle.
     
> I can say the same thing about my PUR filter - in my
> experience it works fine. But I haven't tested it so the statement is
> meaningles. I've never gotten sick while using it but then maybe I never 
> filtered any bad water.
     
The statement isn't meaningless, it's just packs less meaning than a 
rigorous scientific test. Next time we go out on the trail we'll go 
together and conduct an experiment on your pur filter. I will select the 
stream from which I will drink untreated water. You will drink only boiled 
or pur filtered water. If I get sick and you don't you'll have sufficient 
empirical evidence to state that the pur filter works.
     
> I'm just questioning the claims from this little 
> pen.
     
And I'm just trying to find out the basis for your questions about this 
little pen, pointing out my *experience* with solar radiation, uv light, 
and drinking water.
     
>       I stand by the original statement - but I need to clarify. Solar 
> radiation may purify but it takes a long time. For this small pen to do 
the
> job in a short period of time would take a lot of energy output.
     
I agree with the reasoning so far as it goes, but don't agree that this 
reasoning explains why a uv pen ought not be trusted in theory to disinfect 
a cup of water, IF we believe the specs on the pen and the tables for uv 
energy necessary to knock out specific pathogens.
     
> A milliwatt second per centimeter squared is just energy per unit area 
> (Joules/square meter). Energy is expressed in Joules which are 
watts/second,
> and area is expressed in square meters. 
     
Just using the industry's units instead of the physics; the numbers should 
work out either way, shouldn't they, as long as we make the necessary 
conversions.
     
> http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
     
Thanks! I needed that.
     
> A solid state laser (semiconductor) could be 
> possible in the uv range though.
     
Tell me more ... maybe we can beat the steripen folks to the market with a 
better pen.
     
>       Keep looking. This is ALWAYS the test to see if a claim is valid. If 
> a product makes claims that are legitimate then they will get it tested.
     
You bet they will. They'll get tested by the competition and by the 
customers who use the product, and when they get sick they'll go after the 
manufacturer to test them again against twelve peers.
     
> Please don't take my comments as being critical of your research or 
ideas. I
> am just a skeptic and I believe in analyzing these things very critically 
> from a scientific/engineering standpoint. Keep researching and let us 
know
> if you find any independent test results. I will be the first one to swap 
my
> heavy PUR filter for a ster-pen if it really works!
     
I don't take this stuff very personally, I can assure you. I am interested 
in the subject matter and appreciate the presence here of people more 
educated in the scientific issues than me. I'm pretty much of a skeptic, 
too. I value your comments ... for instance, my memory was clearly wrong on 
cube vs square thing, but you knew enough to know what I was trying to 
remember for two or three decades ago.
     
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