Well Waldo here goes.
First the errors that you made are pretty much the same that most make. Since you are trying to write this article for you webpage, in a technical matter, we should then get things straight. I explained these before but they did not sink in but that is my fault as my approach was wrong and I assumed some things.
PSU (Practical Salinity Scale
There is not such thin as PSU, despite you see it everywhere, it si PSS. In recent years some oceanographer tried to take PSS and make it PSU with a unit in o/oo. True PSS has no unit, it is just 35.00 for NSW. Here is a letter explaining it.
This is an e-mail distributed by Gay Ingram and Frank J. MIllero:
Recently I have become upset by the use of the term PSU by oceanographers and some marine chemists in
published articles. The term apparently is used to denote the use of the Practical Salinity Scale and is an
abbreviation for Practical Salinity Unit.
As a member of the Joint Panel on oceanographic Tables and Standards that was instrumental in the
development of the international equation of state of sea water and the practical salinity scale, I am amazed
at the practice that seems to have been adopted by oceanographers in using PSU. The practical salinity
scale was defined as conductivity ratio with no units. A seawater sample with a conductivity ratio of 1.0
at 15 Celsius with a KCl solution containing a mass of 32.4356 g in a total mass of 1 kg of solution has a
salinity of 35.000 (no units or ‰ are needed). The salinity (0.1 to 40) and temperature (0 to 40 Celsius)
dependence of this ratio for seawater weight evaporated or diluted with water led to the full definition of the
practical salinity scale. This definition was adopted by all the National and International Oceanographic
Organizations. It also was published in all the journals publishing oceanographic studies.
Somewhere along the line oceanographers started to use the term PSU (practical salinity unit) to indicate that
the practical salinity scale was used to determine conductivity salinity. This apparently resulted from the
previous use of o/oo to represent parts per thousand which some oceanographers felt was a unit. Some
authors use the PSU term for salinity that has not been measured by conductivity or is outside of the salinity
range of the original measurements. The bottom line is that salinity has always been a ratio and does
not have physical units. The use of the term PSU should not be permitted in the field and certainty not used
in published papers. Whenever the practical salinity scale is used to determine salinity this should be stated
some where in the paper. The use of the term PSS can be used to indicate that the Practical Salinity
To this
Salinity
You may want to add
The practical salinity of seawater is defined as the conductivity ratio, K<sub>15</sub>, where
K<sub>15</sub> = Conductivity of seawater/ Conductivity of std KCL. This ratio is;
S = 0.0080 - 0.1692 K<sup>1/2</sup> + 25.3853 K + 14.0941 K<sup>3/2</sup> - 7.0261 K<sup>2</sup> + 2.7081 K<sup>5/2</sup>
Salinity Based on Conductivity or K<sub>15</sub>
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_01.htm
Density
Chemical oceanographers do not revert back to some std such as 15 C, D is just D. Here is an example I used before with Dr. Kelly's calculator. He is an expert on D Salinity relationships. They do not go back to 15 C
Type in 25 C and 35 ppt = 23.43
More on Density issue
http://www.es.flinders.edu.au/~mattom/IntroOc/notes/lecture03.html
Her is another one to paly with
http://fermi.jhuapl.edu/denscalc.html
Specific Gravity
ót = 103(ñ/ñm - 1)
NO !!!!!
That is a Density equation NOT Sg
Yes the math is correct but you are making it way to complicated with that equation.
Easier
ót = p -1000 or if using g / mg
ót = (p - 1) x 1000
Again ót or t =15 is for DENSITY. Chemical oceanographers rarely every use Sg buy D as ót or EC @ 53, 070 uS = 35.00 @ 25 C
Hanna is using ót for Density. The real symbol Specific Gravity is s.g. so.......... s.g. <sub15</sub>. Their meter does not measure or give Sg. So, it is not wise to compare it to a refract which is a function of Sg. Even if the numbers look right. The refract should be calibrated in PinPoint 53 mS and the Hanna the same solution for EC in Us/mS.
I know they saying their meter is measuring Sg but it is not Sg but Density. Proof here
Density of seawater at 15 C for 35 ppt = 1.02597 (same number you have in your table)
Sg of seawater at 15 C for 35 ppt = 1.0269
Sg is usually about ~ .001 higher than density when using a 15 C hydrometer.
For example, many refractometers display the little symbol d20/20 in the SG scale - this means the density of sea water at 20°C divided by the density of pure water also at 20°C. Confusing?
No, not confusing, that is the definition of Sg, only it is stated often as the mass of a unknown sample of water / mass of fresh water of the same volume.
Specific Gravity is defined as the ratio of the density of sea water to the density of pure water
For us
A common reference temperature for many hydrometers is 15.6°C/15.6°C. This was chosen I believe because most of the ocean is at or close to this temperature. Also because the PSU is defined at this temperature, and many researchers uses hydrometers to test Specific Gravity, which is subsequently calibrated to this standard (and sometimes 20°C or 25°C).
Nope seawater has nothing to do with it. And it is not 15.6 C but 15C/59F. You will find it everywhere. It is the best temp for most lab studies of any kind, after that is 20C. In recent years, US people wanted to get away from C for some unknown dumb reason and 49 C did fit not right, so they started making hydrometers set to 60 F/15.6C. A real TRUE hydrometer, like we use in geology, is 4 C. I have never figure it out yet why one wants a hydrometer calibrated at some temp other than waters true max density of ~ 4 C. It makes no sense
So you look in a table and see what the actual value is at say 30°C (the sample's temperature) for a reference of 15°C - in this case it is a factor of 1.0217/1.0259 = 0.996, thus the correct value is 1.023/0.996 = 1.027 if the Salinity was 36.5ppt
That is a confusing mess and not needed. I know what you are TRYING to do.
If you take 15 C hydrometer put it in water @ 30 C and get a "observed reading" of 1.027 = 40.8 ppt and not 36.5 ppt. If the salinity wanted was 36.5 then you want it to read 1.0238 in that 30 C water. And this is all one needs to know.
People in this hobby are not suing 15C hydrometers but 25 C/77F hydrometers. I have a program that generates SG tables and I posted the calculator so your math is wrong somewhere.
Here it is again
http://www.reefkeeping.com/issues/2004-07/rhf/conversion.htm
Although I should not throw this in to the Hoge-Poge but the max density of FW is a far cry from seawater, which is - 3.61 C (25.5 F) and not at 3.98 C as FW
Both a hydrometer calibrated at 15°C and at 25°C would produce a value of 1.027 for sea water at 30°C and Salinity of 36.5ppt.
I don't know how you got that but No.
15 C @ 30C, reading 1.027 = 40.8 ppt
25 C @ 30C, reading 1.027 = 38.0 ppt
Also read these;
Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php
Temperature Corrections for Hydrometers
http://reefkeeping.com/issues/2004-07/rhf/index.htm
Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm
Specific Gravity Measurement
http://www.advancedaquarist.com/2002/1/chemistry
Using Conductivity to Measure Salinity
http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=1804
So oceanographers and aquarists alike speak once again the same language - based on 15°C.
Nope they talk in 15C and we talk in 25 C, big difference. A 15 C in 25 C water for 35 ppt = 1.0243 = 35 ppt and a 25 C in 25 C water = 1.0264 = 35 ppt. What your attempt is that 25 C in @25 C water of 1.0264 = 35 ppt is the same as 15C in 15 C for 35 ppt, which actually is not 1.0264 but 1.0269 = 35 ppt.
Temp Density(SWEoS) ót ó15 Refractometer
15°C 1.02597 1.0260 1.0260 1.0265 (35ppt) 20/20
20°C 1.02465 1.0247 1.0260
25°C 1.02334 1.0234 1.0260
27°C 1.02270 1.0227 1.0260 1.0265 (35ppt), 20/20
Ok what does this mean. They have set the Hanna to density and not Sg. Hydrometers are set to sg and not density. Who's refract are you using ? Does it have ATC ? Refracts always measure to low in seawater by 1.5 ppt.
What does this mean ?
ó15 = Density corrected back 15 C
ót = Actual Density at the give temp
