# Precision way to measure liquid volume? (avoiding capillary forces error)

Capillary forces is an enemy of every volume measurement for a rigid body or liquid.

However, for rigid bodies there's that nice method used by jewelers: take a glass with water, measure its weight, than "hang" the body in the water so that it only displaces water but doesn't apply any force (part of its weight) to the bottom of the glass and measure the weight of the glass again. The desired volume is $V = {{W_1 - W_2}\over{g \rho}}$ and there's no error due to capillary forces (the only thing is to make sure there's no bubbles attached to the rigid body).

Now I wonder if there's anything that beautiful to deal with measuring volumes of liquids, especially precision measurement of small volumes of such bad liquids as cyclohexame (volatile, damages some types of plastic). Are you aware of any?

Edit: it is implied that the density of the liquid is unknown.

• This is very strangely phrased. What you mean is weighing the glass of water, then hanging the item to be measured in it, right? So the second „it“ refers to the item, right? – Ludi Jul 15 '18 at 18:42
• Also, I do need to submerge the thing to which my solid will be affixed and include it to my measurement of W1, right? – Ludi Jul 15 '18 at 18:54
• Hi @Ludi, thanks, I've edited the question to clarify it (hopefully). You are correct in both of your questions in the first comment. Your next question is trickier. If you want to use a support, not only it should be included to the measurement of W1 but also you have to account for extra volume it will take when the water level rises. As far as I know, usually a thin string is used to hang the body; the string should have both neglectable volume and low wettability (so that it doesn't draw the water on itself). I'm not 100% sure if actually water is used as the liquid, though. – YakovL Jul 15 '18 at 21:41
• @Ludi by the way, here's a nice demo of the method: youtube.com/watch?v=-Hpg214Kk_U (and like I though, for more accurate measurements, another liquid is used: mecury!) – YakovL Jul 15 '18 at 21:54

A bottle named a pycnometer or density bottle (which includes a capillary tube so any excess can be removed) is used to get a precise volume of a liquid, for purposes of weighing to determine a density.

So you don't measure the volume and the mass of a liquid, you fill the bottle with liquid to get a known (calibrated) volume, and then you measure the mass.

In answer to your other question, volume is not additive. 50 ml of water and 50 ml of ethanol gives less than 100 ml of mixture.

Measure mass on a chemical balance. Calculate volume from known density at given temperature.

If you are only interested in density or change in density, you can use the Jeweller's Method in reverse : Weigh an object of known volume $V$ in air $W_1$ and immersed in the solution $W_2$. Then the density of the solution is then $\rho=(W_1-W_2)/gV$.

Or use a high precision hydrometer.

• Appologies, I was asking mostly with a case of unknown density in mind. Actually, the inception of the question was an idea to measure density change of some solvents on adding some solutes available in small quantities. – YakovL Aug 29 '16 at 1:52
• (Volume is not additive, right?) – YakovL Aug 29 '16 at 1:57
• So you are really asking about measuring a change in density, rather than a certain volume? – sammy gerbil Aug 29 '16 at 10:29
• Well, you may put it so, but the mass is relatively easily measured precisely (although may depend on a situation) so measuring density and volume sounds somewhat the same. – YakovL Aug 29 '16 at 21:22