I have had visions of making a quantity of density measuring 'fishing float' type hydrometers. Not as elaborate as the ones you can purchase.
I was thinking along the lines of making about 10 or so, of what would effectively look like glass ampoules, with a small weigh inside (lead shot).
Each would sink at a certain densiy of the liquid they would be placed into.
You would simply put all of them into the liquid and leave them there and you would know at a glance what was the density by observing which ones were
floating and which were not.
The temperature would be about 70C.
Would this work?
It is expensive to purchase 70C hydrometers. I suppose you could purchase 20C ones and make an allowance for the higher temperautre (or is it that
simple). Two decimal places of accuracy is sufficient.
But if you are looking at the same mixtures (ethanol and water) over and over, you should be able to come up with a calibration curve for the 20C ones
to adjust them to 70C. We used to have a bunch of distillation experts on here, but they seem to all be gone, likely either the revenuers got them,
or they are too drunk to type. But I have some friends who like to dabble in that area. You could make your own, but easier to just pick a sample,
use the 20C ones and record the results, then cool the sample to 20C, and see what the shift is. If you do that a few times, you should be able to
see what the shift is from 20 to 70C, and be able to back calculate the 70 C numbers OK. I have done similar things for mixed solutions and got good
results to within 1%. The density of ethanol/water solns is also well known, so that might work also, but hard to keep a sample at a set temp.Sulaiman - 10-11-2020 at 19:35
Density compensation data vs concentration and temperature is available online for most mixtures.
I'd buy a hydrometer suitable for the range of densities expected and use compensation data.
You can calibrate a diy or commercial hydrometer,
A 100ml (+/- 1ml) measuring cylinder with scales accurate to +/- 1g will give about 1% error... 2 significant figures,
A 100ml (+/- 0.1ml) volumetric flask with scales accurate to +/- 0.1g will give 3 significant figures.
(additional compensation for buoyancy due to air required) yobbo II - 11-11-2020 at 17:19
Thanks for replys.
I am trying to measure the density of solutions of salts. If I take a sample it cools and you get precipitation.
I see a naglene 1.2 to 1.4 (approx.) (plastic) hydrometer on ebay buts it does not want to be in an aggressive environment. I think I need glass.
I'd be interested to know how you will achieve this level of precision.
If I were doing this I'd use a single "float" heavy enough to sink under all densities, attached to a loadcell with a suitable thin wire or string.
Then you could also include a thermocouple, and between the force on the loadcell and the temperature measurement you'd be able to calculate density.
Use a raspberry pi with a small LCD screen for the calcs and display.
Benefit is automatic compensation for temperature, and a simple parameter change for different compensation factors for different liquids.
But then I'm an EE so I automatically lean towards electronic solutions. yobbo II - 12-11-2020 at 16:43
I have a mechanical weighing balance and I will have a go at that.
