January 4, 2008
Hello All and Happy New Year! 
As a science educator in West Virginia, I am wondering what the conductivity measurements will tell you about the ocean's water?  

Can you recommend a simple tool in which to measure conductivity?  We are collaborating with some teachers in Belize on water ecosystems and we would like to compare conductivity between fresh and salt water samples.

Thanks much, Jenny

Jenny Bardwell
HSTA Curriculum Coordinator
West Virginia University
Morgantown, WV  26506

Dear Jenny:

Conductivity depends on the number of ions present in a solution, so the measurement of conductivity provides a measure of salinity. It is strongly dependent on temperature, so you need to measure the temperature at the same time, and correct for temperature to get a good value of salinity.

There is a simpler tool to measure salinity that can be used in the field, although it does not have the resolution of a conductivity measurement. The tool is a refractometer, and it depends on the change in the angle of refraction of light as it passes through solutions of different salinities. It is very simple to use: A drop of the liquid is placed on a glass and held up to the light, and the angle of refraction and its conversion to salinity is read directly off a scale. It is good for measurements where there are major differences in salinity—such as between fresh and saltwater samples. And they are relatively inexpensive (less than $50).

Thanks for the question, and I hope you continue to follow along with our cruise.

Susan Humphris

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