The subject of various alternative means of determining salinity previously came up in this thread where I dabbled (in what I now see was an amusingly over-simplified way) with the idea of using a couple of simple tools to determine salinity by calculating the density of your tank water.
I have recently revisited this idea, and have some interesting things to report.
The method I describe in this thread appears, after some initial testing, to be able to provide salinity results that can be accurate to +/- 0.3, or SG results that are +/- 0.0002, requiring only a few simple tools, provided sufficient care and attention to detail is given to certain steps of the process.
The density ρ of a substance is equal to the mass m divided by the volume V: ρ = m/V. If you know the mass of a given volume of your tank water, then you can determine the density.
Salinity is frequently expressed in terms of specific gravity, which is the density of a substance relative to the density of water at the same temperature. So, in order to determine specific gravity from density, then the temperature must also be known.
If the mass, volume, and temperature of the sample are known with sufficient accuracy, then the specific gravity can be determined, and salinity can also be determined.
The basic idea that I floated in the previous thread is that one might be able to take, for example, a 100 mL volumetric flask, weigh it empty to establish the tare, fill it with tank water to the graduation line, weigh it a second time, and subtract the tare weight to determine the weight of the sample. In the example I gave, I did the test with everything at 20C, which greatly simplified everything. I also attempted to estimate the method uncertainty, to see what sort of confidence I could have in my result.
Since then, I have spent more time thinking about and reading about the process I was attempting and I am now humbled, amused, and embarrassed at how many things I got wrong in that thread. I believe that the approach to the subject I am positing in this thread is more well thought out, and more correct, in terms of both the science and the math. I also have recently had the good fortune of being required as a part of my job to develop a custom interface between numerous Anton-Paar DMA5000 densitometer instruments and our LIMS (Laboratory Information Management System). As a necessary part of this work, I am required to run samples on the densitometer while testing the interface I am developing, providing me an excellent opportunity to run as many samples as I desire on this instrument, which can determine the density and specific gravity of liquid samples to six decimal places!
More to come.....
I have recently revisited this idea, and have some interesting things to report.
The method I describe in this thread appears, after some initial testing, to be able to provide salinity results that can be accurate to +/- 0.3, or SG results that are +/- 0.0002, requiring only a few simple tools, provided sufficient care and attention to detail is given to certain steps of the process.
The density ρ of a substance is equal to the mass m divided by the volume V: ρ = m/V. If you know the mass of a given volume of your tank water, then you can determine the density.
Salinity is frequently expressed in terms of specific gravity, which is the density of a substance relative to the density of water at the same temperature. So, in order to determine specific gravity from density, then the temperature must also be known.
If the mass, volume, and temperature of the sample are known with sufficient accuracy, then the specific gravity can be determined, and salinity can also be determined.
The basic idea that I floated in the previous thread is that one might be able to take, for example, a 100 mL volumetric flask, weigh it empty to establish the tare, fill it with tank water to the graduation line, weigh it a second time, and subtract the tare weight to determine the weight of the sample. In the example I gave, I did the test with everything at 20C, which greatly simplified everything. I also attempted to estimate the method uncertainty, to see what sort of confidence I could have in my result.
Since then, I have spent more time thinking about and reading about the process I was attempting and I am now humbled, amused, and embarrassed at how many things I got wrong in that thread. I believe that the approach to the subject I am positing in this thread is more well thought out, and more correct, in terms of both the science and the math. I also have recently had the good fortune of being required as a part of my job to develop a custom interface between numerous Anton-Paar DMA5000 densitometer instruments and our LIMS (Laboratory Information Management System). As a necessary part of this work, I am required to run samples on the densitometer while testing the interface I am developing, providing me an excellent opportunity to run as many samples as I desire on this instrument, which can determine the density and specific gravity of liquid samples to six decimal places!
More to come.....