When testing biodiesel for presence of water after adding the carbide to the biodiesel, the indicator fluid drops below the starting point and since there is always some degree of water present, what is the possible reason for this? What am I doing wrong?
Hi Jock, imakebiodiesel is really your man to answer this one.He is the manometer expert.
I think it is caused because the temperature of the sample is very slightly lower than the
air in the headspace of the jar.So when you start to swirl the air will contract for a few seconds
until the reaction gets going.Just release the cap for a second and let the level go back to its
Hi Jock, over the last couple of years several users have drawn my attention to this effect. In some cases the reading rises slightly when the jar is closed. I think this is caused by the seal in the lid being tightened and the air in the headspace being compressed.
In your case the reading drops which as Dgs suggested may be the air in the headspace cooling in contact with the liquid sample. If the headspace in your jar is overly large or very small these effects are worsened. 100 gms of biodiesel should a little more than half fill your jar.
However, whatever way the level moves in those first few seconds before you start shaking the sample, simply note how much it moves and add or subtract that from your final reading because whatever is causing it, its not the water content thats causing it.
I experience this movement at the start of tests often usually a drop. So I took a 2cm piece of the same clear tubing the manometer is made of, split it and placed it over the manometer tube. Then when I place the lid on the jar if the level moves I slide the piece down to where it dropped to and take my reading from there. Testing the same sample on different days gave comparable results after compensating for different initial drops.
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