Potometers

Peter Sigsworth

COMMITTEE
We use the EISCO potometer with a few adaptations:
1. permanently fix the clips with screws and glue (instead of the pathetic two sided tape)
This makes everything more robust
2. Remove the 5ml syringe and replace with a 100ml reservoir

This improves the machine by allowing you to feed the plant off the reservoir and I have set it up and left it all weekend - still works on the Monday morning (all be it a bit slower due to the stem getting blocked by infection).
3. Everything fixed on one clamp stand

Kit taped down, top clamp gently holding the plant second clamp holding the reservoir. The whole set up then can be easily transported to different locations.
Use the tap to control what you are doing . - in line for running, top and right to feed off reservoir, right and bottom to zero the capillary tube (using the liquid from the reservoir with care)

The good thing about the EISCO is you can remove the tube connector and fix it on the stem under water without any Vaseline or vacuum grease just cut it at an angle, push on to one end then seal with several twists of elastic band. Join up to machine under water. I use laurel because the stems are the right size are woody so they push into the tube easily and are evergreen so you do this at any time of year


 

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Peter Sigsworth

COMMITTEE
thanks, we will try this - we can never get the potometer to work! we will try this adapted method
The main secret is getting the seal on the cut stem - all under water and using the elastic band which produces a flexible seal without use of Vaseline.

We are buying several of the EISCO models because using the side reservoir you can set them all up and leave them for a couple of days if you want - all the students do is use the 3 way tap to connect from the capillary tube to the stem to start the monitoring and then from the reservoir to the capillary tube to zero it again and so on.
 
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Peter Sigsworth

COMMITTEE
Here is an instruction sheet for students to control their EISCO photometers using the 3-way stop cock
 

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Very good but twice the price of the EISCO ones and not as easy to set up. My adaptation to the EISCO ones means you can set them up at least a day before you need them.
the saps ones keep as well, we have one ganong potometer because it the same as the "exam pictures",
 

Peter Sigsworth

COMMITTEE
the saps ones keep as well, we have one ganong potometer because it the same as the "exam pictures",
Depends on which exam board you're following and they may use a different one next time. The two main types are mass and bubble the EISCO and Ganong are bubble but there are several different types of bubble potometers - 'Darwin', 'Simple', 'Philip Harris', 'Ganong', 'Thoday', 'Farmer' to name but a few - Saps use home made ones and many suppliers use their own designs like the Philip Harris and Lascells.

All I'm trying to do is help those who find photometers difficult to set up and use. My experience with most of the different designs led me to recommend the EISCO model for it's value and ease of use. So I've done an easy to follow 'crib' sheet to get successful results.
I do agree that we should aim to use equipment which matches possible examination questions and so you are right to stick to the Ganong - if you can get it work easily.
 

Peter Sigsworth

COMMITTEE
I use parafilm instead of vaseline for sealing...it works well
Don't need to use any sealer if you use the elastic band method
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