"Carl 1 Lucky Texan" wrote in message
m...
David Hare-Scott wrote:
"Mr.pH" wrote in message
oups.com...

hob wrote:


Does anyone have suggestions for a good quality PH meter.......Digital

or

analog meter, doesn't matter, provided that it is reliable. The one I

got

from my local garden center reads 7 for all areas of my garden. I

knew it

was a dud when I placed it in pure lime juice, and it still read a PH

of

7.

All the meters that I know work on the same principle - bascially, they

read

the electric potential between two parts (metals) of the shaft, or the
electric potential between two side-by-side different-metal shafts,

using

the soil.

Check out this site for pH meter and pH measurements details:

http://www.ph-meter.info

Best,
Mr.pH



Interesting site. How is it relevant to the original question? Are
there
any glass electrode portable systems suitable for use in the garden?
How
much do they cost? For garden or agricultural purposes why would you
need
accuracy down to decimal points of a pH unit?

David



Although the site is somewhat user hostile, there are explanations of pH
strips and pH papers/indicators. Plus, I see no reason a 'pen' or probe
type device couldn't be used in a soil slurry or other very wet, soil
derived solutions.

Bottom line for me - I have two portable probe-type "garden-style" ph
meters - neither works in water (tried them for fish tank, tap water, boiler
water, etc.), but both work just fine in moist mediums.

Why is that? I believe the reason the portable non-battery probes don't
work well in fluids is for the same reason they don't work with well with a
dirty probe -
Using a dirty probe defeats the insulator because it provides a current
path across the insulator, just as immersing the probe in a conducting fluid
defeats the insulator because it also provides a path across the insulator.

----------
As I said, the portable types (without batteries) need a certain current
flow through the meter to make the meter move, and that flow is from the
potential difference in the two measuring elements, flow caused by the
imbalance in the hydrogen and hydroxyl in the measured medium (we are trying
to measure the "free" hydrogen).
The probe materials each gather their hydogen or hydroxyl, and the meter
reads the draining of those two pools of different charges through the meter
circuit.

Water is hydrogen hydroxyl ( H+ OH-, or more commonly H20). It is a
conducting medium.
Having the probe insulator immersed in fluid water will have the same
effect on the insulator and circuit as having a dirty probe insulator -

fwiw


And it IS likely, especially given the difficulty of
soil testing as provided in the other ratehr good link, that decimal
point accuracy means little - but if it comes along with an inexpensive,
convenient, long shelf life piece of test equipment, I see no problem
with that. Some folks may find a way to use a pen or probe for multiple
duty - soil, tropical fish, pond, etc.




Carl


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