Simple experiment:

I was getting some water to drink, a question came up in my mind:
What is more conductive, saliva or tapwater?
The answer kind of suprised me:
I used a Fluke DVM, the probes about 1cm apart in a drop of water, more than a drop, about 2 cm wide, and saliva about the same size.
Water started off at 6.5 megohms but dropped down to 3.6 megs after a minute or so.
Saliva started out at 4.5 megs and went UP to 6.5 megs.
I used probes with differant colors so there may have been some
electrochemistry going on interfering with the meaurements and I should use noble metals, gold or platinum probes to eliminate that but why should there be the opposite time based reaction between the two?

Originally posted by sonhouse
What is more conductive, saliva or tapwater?

As far as I know pure water is an insulator. So it all depends on what substances are dissolved in the two. It may be affected by which tap, and what you ate before spitting.

Originally posted by twhitehead
As far as I know pure water is an insulator. So it all depends on what substances are dissolved in the two. It may be affected by which tap, and what you ate before spitting.

Pure water, which we use in our industry, it's called DI water, de-ionized water has a resistance of about 18 megohms per square cm.
which is about as insulating as water can get, maybe a bit better.
Regular tapwater is fairly conductive, as anyone can find out if you drop a plugged in appliance into a bathtub of water but I thought it was interesting the reaction of the two, going in opposite directions like that. I had not eaten anything for about 6 hours and had drunk some water earlier.

Originally posted by twhitehead
As far as I know pure water is an insulator. So it all depends on what substances are dissolved in the two. It may be affected by which tap, and what you ate before spitting.

The purest water possible is still a mix of CO2 (surprise?) and CO- and O+. There is always a small fraction of ions. These come from spontanous braking of bonds in the CO2 molecule. They reattach rather quickly, but there will still be a fraction of ions. These ions conduct electricity.

Originally posted by FabianFnas
The purest water possible ..

Are you saying that whatever we do, we cant keep CO2 out of water? I don't believe that. It might still be hard to experiment on it though as exposure to air would cause contamination. Maybe the experiment could be done in an oxygen chamber with the experimenter either outside or in scuber gear.

Originally posted by FabianFnas
The purest water possible is still a mix of CO2 (surprise?) and CO- and O+. There is always a small fraction of ions. These come from spontanous braking of bonds in the CO2 molecule. They reattach rather quickly, but there will still be a fraction of ions. These ions conduct electricity.

Thats not what we get in our industry, semiconductor grade water conducts about 23 megs/square if I remember right, no CO or anything, everything removed by active ion attractor filters and reverse osmosis filters and a large dose of UV to kill organics, all that after ion resin beds and rough filters. What we end up with is H20 and hopefully nothing else, anything like CO and O radicals would cause havoc on the production of silicon wafer technologies like electronics or in my case, optical integrated circuitry.

Originally posted by sonhouse
Regular tapwater is fairly conductive, as anyone can find out if you drop a plugged in appliance into a bathtub of water but I thought it was interesting the reaction of the two, going in opposite directions like that. I had not eaten anything for about 6 hours and had drunk some water earlier.

The fact that it changed over time implies a chemical reaction. Could it be that your tap water is acidic and your spit alkaline, or the other way around?
My tap water is acidic - I know because I had problems with that in my aquarium.
Also if there is a lot of carbonates in your water it could be building up deposits on the terminals - the same applies to spit. You may find that deposits happen whether or not your probes are reactive.
I also thought that passing electricity through water causes electrolysis of the water which will cause an increase in concentration of any dissolved substances which may affect the conductivity depending on what substances are dissolved.

Redo your experiment with increased volumes and see if the volume affects the result.

Originally posted by twhitehead
The fact that it changed over time implies a chemical reaction. Could it be that your tap water is acidic and your spit alkaline, or the other way around?
My tap water is acidic - I know because I had problems with that in my aquarium.
Also if there is a lot of carbonates in your water it could be building up deposits on the terminals - the same applies ...[text shortened]... solved.

Redo your experiment with increased volumes and see if the volume affects the result.

Can't change the volume of my saliva very well, but it could use some litmus paper, that would tell acid/alkaline. Forgot about that.
There are probes that measure the resistance of DI water, btw, DI water in itself is corrosive, it corrodes stainless steel for instance, I know that for a fact! I used to work on ion implanters and ten years ago the high voltage end (200,000 volts and up) had to be cooled so you needed a highly insulating fluid, which in the day was liquid freon, VERY high resistance. That ended when it was discoverd the stuff was eating away at the ozone layer so we had to come up with a substitute, and what we used was DI water (using ID of course🙂
It insulates well enough that you can have polyflow tubing go across a half million volt barrier and not arc and then provide the cooling needed for the electonics. The big caviat was this: it ate all the SS hardware it came into contact with, so we had to change all the hardware to some kind of plastic, preferably teflon. You can't imagine how many of those little fittings I changed on a bunch of ion implanters till they started coming out of the factory already modified.
Anyway, back to the drawing board and see what is acidic or alky.

Originally posted by FabianFnas
The purest water possible is still a mix of CO2 (surprise?) and CO- and O+. There is always a small fraction of ions. These come from spontanous braking of bonds in the CO2 molecule. They reattach rather quickly, but there will still be a fraction of ions. These ions conduct electricity.

Oh, sorry sorry sorry! (Stupid me!) 😳
Change all CO2 to H2O and then everything make sense.
This is what I should have written:

The purest water possible is still a mix of H2O (surprise?) and OH- and O+. There is always a small fraction of ions. These come from spontanous braking of bonds in the H2O molecule. They reattach rather quickly, but there will still be a fraction of ions. These ions conduct electricity.

Again Sorry...

Originally posted by FabianFnas
Oh, sorry sorry sorry! (Stupid me!) 😳
Change all CO2 to H2O and then everything make sense.
This is what I should have written:

The purest water possible is still a mix of [b]H2O (surprise?) and OH- and O+. There is always a small fraction of ions. These come from spontanous braking of bonds in the H2O molecule. They reattac ...[text shortened]... y, but there will still be a fraction of ions. These ions conduct electricity.

Again Sorry...[/b]

Thats a bit better! Those residual ions and the polar nature of H2O is what makes it corrosive when there are no contaminates to already have attracted the polarity to a fixed place. That's also why you don't want to drink DI water, it upsets the electrolyte balance in the body, or at least in the stomach.

Originally posted by FabianFnas
The purest water possible is still a mix of [b]H2O (surprise?) and OH- and O+. There is always a small fraction of ions. These come from spontanous braking of bonds in the H2O molecule. They reattach rather quickly, but there will still be a fraction of ions. These ions conduct electricity.[/b]

I believe that that is why electrolysis works.

Originally posted by twhitehead
I believe that that is why electrolysis works.

Electrolysis usually requires the addition of ions beyond what you get in tapwater, for instance. The high school experiment of making H and O requires one to add some salt which ionizes easily and creates a very conductive fluid, brine is very conductive, then the electrodes, + and - with about 300 volts DC across them will start making O2 and H pretty quickly.
The big caveat for doing that to produce hydrogen for cars is that means is only about 3 % efficient, so you put in 97 watts of energy in to get three watts out in hydrogen, so more efficient means have been worked up and that is an on-going project.