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

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #251

The salinity of seawater can be determined by measuring a wide range of properties. From a table of how these properties change with salinity, the salinity can be determined.

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

List all that you think cannot work

A. Electrical conductivity at a particular AC frequency
B. Speed of sound at a particular frequency
C. Speed of yellow light
D. Absorption of yellow light
E. Density at 30 degrees C
F. Boiling point at 1 atmosphere pressure
G. Freezing point
H. Viscosity at 30 degrees C

Good luck!










































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[dragon99]

A duck!

 

[CircleCityBill]

Assuming the sample is not first fed into an acetylene furnace, I'll choose D.

 

[Randy Holmes-Farley]

Assuming the sample is not first fed into an acetylene furnace, I'll choose D.

Good point. lol

 

[SDReefer]

I'm going to guess A and C. A since a conductivity meter would also measure other ions present in the water and C since I'm assuming the speed of light is constant.

 

[JimWelsh]

There *may* be other methods in the list that CANNOT work, but I'm certain that "D. Absorption of yellow light" is one method that simply cannot work to measure salinity. I want to add that C is a sneaky one Randy put in the list, but I use that method quite regularly myself to measure salinity, and I'm certain that others reading this do, too.

 

[drblakjak55]

All these ways work to measure salinity.

 

[rkpetersen]

A? (because AC current is mentioned; not sure if that works.) Perhaps D although not sure if that's impossible or just too insensitive to be practical.

 

[Mark Gray]

I think D

 

[Dburr1014]

D, cuz if you can measure the speed of yellow light, then how could you measure it if it's also being absorbed? Readings would be skewed. {I think}

 

[Randy Holmes-Farley]

I want to add that C is a sneaky one Randy put in the list, but I use that method quite regularly myself to measure salinity, and I'm certain that others reading this do, too.

lol

Quite.

 

[Randy Holmes-Farley]

D, cuz if you can measure the speed of yellow light, then how could you measure it if it's also being absorbed? Readings would be skewed. {I think}

Actually, that's not impossible. At risk of giving away answers, or getting too nerdy (very likely ) , the speed of light is part of what goes into refractive index. It is the "real" part of the refractive index. While refractometers do not measure it, there is an "imaginary" part of the refractive index, which is the absorption. Literally, by imaginary, I mean the square root of negative one (i).

Here's wikipedia's discussion:

https://en.wikipedia.org/wiki/Refractive_index

Complex refractive index

When light passes through a medium, some part of it will always be attenuated. This can be conveniently taken into account by defining a complex refractive index,

n = n + ik

Here, the real part n is the refractive index and indicates the phase velocity, while the imaginary part κ is called the extinction coefficient — although κ can also refer to the mass attenuation coefficient—[28]:3 and indicates the amount of attenuation when the electromagnetic wave propagates through the material.[1]:128

 

[Dburr1014]

Oh that's way above my pay grade.
Lol

 

[JimWelsh]

Actually, that's not impossible. At risk of giving away answers, or getting too nerdy (very likely ) , the speed of light is part of what goes into refractive index. It is the "real" part of the refractive index. While refractometers do not measure it, there is an "imaginary" part of the refractive index, which is the absorption. Literally, by imaginary, I mean the square root of negative one (i).

Here's wikipedia's discussion:

https://en.wikipedia.org/wiki/Refractive_index

Complex refractive index

When light passes through a medium, some part of it will always be attenuated. This can be conveniently taken into account by defining a complex refractive index,

n = n + ik

Here, the real part n is the refractive index and indicates the phase velocity, while the imaginary part κ is called the extinction coefficient — although κ can also refer to the mass attenuation coefficient—[28]:3 and indicates the amount of attenuation when the electromagnetic wave propagates through the material.[1]:128

I imagine that this contradicts me, then.

 

[ChrisOFL]

I say you could use all of those to test for salinity. They all seem like physical properties of water that are directly effected by salinity from what I can tell.

 

[Cory]

I dont know but id love to measure salinity with the speed of sound! Probably more prone to error though than light?

 

[siggy]

I dont know but id love to measure salinity with the speed of sound! Probably more prone to error though than light?

I noticed that a range of accuracy is not specified

 

[Cory]

I noticed that a range of accuracy is not specified

You have one? love reef toys

 

[siggy]

I have several ultrasonic and laser switches with feedback, they may show differences but not to the degree I would trust for a reef tank. I could send to someone that knows how to support

 

[Randy Holmes-Farley]

I imagine that this contradicts me, then.

No, I don't think so.