Reef Chemistry Question of the Day #251 Ways to Measure Salinity

[JimWelsh]

No, I don't think so.

But, did you see what I did there?

 

[MnFish1]

They all will vary with salinity - so they could all be used to measure salinity. though many of them dont vary much with pretty big changes in salinity - someone 'could' do it.

 

[Randy Holmes-Farley]

But, did you see what I did there?

Ummmm. Guess not?

 

[pandagobyguy]

Wait so the answer is all of them right?

D is not an option or it is?

 

[Randy Holmes-Farley]

Wait so the answer is all of them right?

I haven't given the answer yet, but no.

 

[JimWelsh]

Ummmm. Guess not?

I "imagine" that your imaginary number answer contradicted.... Oh, never mind.

 

[Randy Holmes-Farley]

I "imagine" that your imaginary number answer contradicted.... Oh, never mind.

lol OK

 

[SDReefer]

What's the answer @Randy Holmes-Farley? This is an interesting topic!

 

[Randy Holmes-Farley]

And the answer is....

Which of the following possible ways to measure salinity cannot work?

D. Absorption of yellow light

All of the other methods vary in a way that one can correlate with salinity, although some may be hard to implement and may have other factors that also impact the answer (e.g., viscosity varies with salinity, but might be skewed by large organic molecules).

Other comments:

A. Electrical conductivity at a particular AC frequency (many reefers use conductivity in this fashion)
B. Speed of sound at a particular frequency (not used by reefers, but does impact measurements made in the ocean)
C. Speed of yellow light (refractometers do this)
D. Absorption of yellow light (cannot work)
E. Density at 30 degrees C (reefers use this when using a hydrometer)
F. Boiling point at 1 atmosphere pressure (salts raise the boiling point by an amount related to the amount present)
G. Freezing point (salts lower the freezing point by an amount related to the amount present)
H. Viscosity at 30 degrees C (the viscosity increase is small, but it rises with salinity)

 

[MnFish1]

And the answer is....

Which of the following possible ways to measure salinity cannot work?

D. Absorption of yellow light

All of the other methods vary in a way that one can correlate with salinity, although some may be hard to implement and may have other factors that also impact the answer (e.g., viscosity varies with salinity, but might be skewed by large organic molecules).

Other comments:

A. Electrical conductivity at a particular AC frequency (many reefers use conductivity in this fashion)
B. Speed of sound at a particular frequency (not used by reefers, but does impact measurements made in the ocean)
C. Speed of yellow light (refractometers do this)
D. Absorption of yellow light (cannot work)
E. Density at 30 degrees C (reefers use this when using a hydrometer)
F. Boiling point at 1 atmosphere pressure (salts raise the boiling point by an amount related to the amount present)
G. Freezing point (salts lower the freezing point by an amount related to the amount present)
H. Viscosity at 30 degrees C (the viscosity increase is small, but it rises with salinity)

Can you explain why

 

[pandagobyguy]

Can you explain why

That is a very broad question.

 

[Randy Holmes-Farley]

Can you explain why

Why absorption of yellow light can't work?

Sure. Suppose your water in your aquarium slightly absorbs light (including yellow) due to the presence of organics because you have inadequate organic export (skimming, GAC, purigen, etc.).

Then you add GAC or ozone or something to make the water clear (less light absorbing).

It works, and your yellow light absorption is much less, but the salinity hasn't changed. So one cannot correlate yellow light absorption with salinity.

Overall, it is because the major ions in seawater that really control salinity do not absorb any yellow light, so there is no change in yellow light absorption as they rise and fall.

 

[Randy Holmes-Farley]

That is a very broad question.

lol

 

[MnFish1]

Why absorption of yellow light can't work?

Sure. Suppose your water in your aquarium slightly absorbs light (including yellow) due to the presence of organics because you have inadequate organic export (skimming, GAC, purigen, etc.).

Then you add GAC or ozone or something to make the water clear (less light absorbing).

It works, and your yellow light absorption is much less, but the salinity hasn't changed. So one cannot correlate yellow light absorption with salinity.

Overall, it is because the major ions in seawater that really control salinity do not absorb any yellow light, so there is no change in yellow light absorption as they rise and fall.

Thanks