Hi Afza,

there are just two things you hve to be aware of the liquid should wet the sample and should not react with it. It should not evaporate quickly. The sample has to be completely immersed how deep the sample is in the liquid does not matter. You should control the temperature of the liquid (accuracy +/- 0.1 °C to have the correct density, for water you can find reliable density data.

We measure ceramics with an accuracy of 0.001 g/cm² if samples have a weight of ~ 10g. The bigger the sample the better the accuracy.

best regards

Frank

@Frank Kern

Thank you so much for sharing your knowledge.

Im measuring density of a metal piece that weighs approximately 3.5 kg. What Ive observed is when I vary the level of object in water the weight varies. Why did this happen?

The density measurement using Archimedes principle is based on Mass/volume. Its accuracy depends how accuate you measured the mass and volume.

For the mass, high resolution /sensitivty scales are needed.

The measured volume has to be the acutal volume: the liquid wets your sample with no bubbles, reactions, penetrations, minimized effects of the suspending wires ( very thin), constant temperature, etc.

I would suggest to use a liquid with a low superficial tension in order to minimise the capilarity meniscus that the liquid forms by interaction with the graduate tube allowing you to measure the liquid height rising to to the object immersion. This should help you in increase the accuracy measure. Also try to work with a graduated tube that is not too small in diameter as it boost the capilarity phenomenon. Low surface tension liquid will also helps in obtain a superior wetting of the object you want to mesure.

If the item is irregular in shape you need to make sure no air pockets are captured. If air was released as you moved item deeper that could explain fluid level change. Also how is it being held? If you are hanging on to it with a pair of pliers, the pliers will displace fluid and make for inaccurate and changing measurement. Best to lower item slowly (no splashing) into the fluid and let go before pliers/hand/forceps/tweezers touch the fluid.

As I answered above I was thinking you had fluid level change, but on reading your comment again... "What Ive observed is when I vary the level of object in water the weight varies." Why would you be weighing the item while it is in the fluid? Here is a good lesson on buoyancy with depth change https://courses.lumenlearning.com/boundless-physics/chapter/archimedes-principle/

I. For the density determination by the Archimedes principle you should preferably use an analytical balance with the capability to weight a suspended mass, including both the sample and the sample suspending system, which shall be partially immersed with the sample while weighting the sample immersed. The maximum weighting capacity of the balance obviously limits the maximum weight of the sample. As the impulsion force then acts both in the sample and on the suspending system, the suspending system should also be immersed without the sample, to determine its own contribution for the overall liquid impulsion. In experimental practice, using a thin metallic suspending wire, yet with low extensibility, can improve the accuracy of such a compensation. A single-fiber string may possibly substitute for the metallic wire. Correction for air impulsion, while weighting the non-immersed sample, is typically neglectable.

II. The impulsion force acting on the sample should be much larger than the force originated by the surface tension on the perimeter of the (suspending) wire/string section crossing the liquid surface; that is another reason for selecting a thin wire/string with high tensile strength. This, besides the balance sensitivity, limits the accuracy of the method for excessively low mass samples.

III. The suspending system should neither oxidize, swell, or react with the suspending liquid. The density of the suspending liquid must be accurately known. A pycnometer may possibly be used to determine its density at the selected temperature for the measurements. The liquid should preferably have low surface tension and low volatility. It should neither react or be absorbed by the sample. Use of water typically limits accuracy, owing to its high surface tension, but can be found acceptable for less demanding measurements.

IV. The temperature of the sample should be homogeneous and stable, besides equilibrated with that of the suspending liquid. The temperature of the suspending liquid should be stable and well controlled; yet without disturbing the accuracy of the weighting procedure.

V. Repeated measurements, with severall samples of the same material, may help to further reduce the experimental error.

VI. The measurement method can be adapted to determine the bulk density of porous samples; cf. my post elsewhere at this forum: https://www.researchgate.net/post/How_to_determine_the_density_of_3d_printed_aluminum_parts_with_Archimedes_method

The Archimedes method is very accurate, provided that

1) no air bubble adhere to the sample, provide good wetting (e.g. use ultasonic bath),

2) you know the density of the suspension liquid as a function of temperature (around room temperature) - measure the liquid density with a pycnometer,

3) you measure the temperature of the liquid and weight of the sample simultaneuosly,

4) you leave all items and sample near the balance for some hours so that they have the same temperature,

5) be sure that the surface of the liquid has always the same height.

Of course the closed porosity influences the measured density, if you want to make sure that you use the density of the material, make sure that you have a zero-porosity sample.

Balances for samples around 1-10g should have 5 decimal places xx.xxxxx. The pycnometer (volume e.g. 5-10 ml) is heavier and should be weighed full/empty with the same balance.

Try to

1) use a very thin filament (wire) for suspending the sample (e.g. very thin Cu wire). It is even possible that the length of the filament (wire) submerged into the liquid is such that its buoancy by the liquid exactly compensates the force of surface tension, which pulls the wire down - we made this on small VN, NbN, MoN... samples . Perhaps this is only possible for small samples and hence small wire lengths submerged in the liquid - of course it depends on the density of the wire and the surface tension wire - liquid. Otherwise do the measurement with and without sample.

2) Use a liquid with a high density, sa that the difference of weight to the submerged sample is highest. We used tribromomethane of around 2.8 g/cm3, of course for samples with higher density than this ;) and determined the density of this liquid as a function of temperature around room temperature with a precision of 2.8xx g/cm3.

Thank you everyone for your valuable suggestions.

Samantha Ryan I'm weighing the sample in water. The sample is suspended in water with the help of wires. The purpose is to calculate the density of object with the help of weight in air and weight in water.

When the position (up and down) of suspended piece in water is changed, the weight varies. So what should be the ideal level of piece in water for accurate measurement of weight in water and hence the density.

Further it should be noted that the weight of metal piece is 3.5 kg and it is in cylindrical shape.

Afza Shahid, unless there is some reason you cannot, I recommend simplifying. Density = mass / volume. Measure the mass with a good analytical balance. Use the water displacement for the volume.

When you only use the weight in air and in water, your uncertainty comes "only" from your balance and the measurement of the temperature : so it is the best way to measure the density. If you measure the volume you introduce other sources of uncertainty (length, diameter, thermal coefficient of expansion).

You can find very usefull advices here :

https://search.bipm.org/bipm/fr/C=eJw9xstygjAUANB8is505cqpWsiSh6COQhFQdNNBckWEJJAQUvz6uurqnA5RkErAhMCE5lLCZOCNolWnADXoLhBD34KTH08AKx6ofXAGfVWgOWqA0vxt3raC*74jC4oYDCAQ!d!HltAh2I3kdVuH5dOKbGVn!dmI7ShaRKth6Tz5Mps6TpLxHlvWjWHDX4aOnwyYmOo!o43aLq4nP71Q4unP1Awif8!2X7oz9K0qQcWHeUnZuZc7T4!bmTflrQtFK*29CE5x6QcH43rhOan1eMSda1brMRxk7SYpx!EcH8PecNOCJ6dQaYydPm2sOpvaUCptu*DaALnXB7NZledBLII9!gP6TWYj?action=s&q=density&x=0&y=0&resetcontext=

there is a very good paper on the measurement of the density of 1.02 kg cylinder of platinum-iridium by C. Goyon.

Hope it will help you

Dear Afza,

think also about gas displacement method instead of liquid one. Yeap, you should find somebody who has such equipment available. Anyway, it can be home made as well, it is not too complex task. Look into internet and literature survey for this subject.

Good Luck !

Hi Afza,

If you use water, my suggestion is to add some droplets of soap in the water. It will reduce the surface tension and thus you should have higher accuracy.

I think the question here is, what are the factors affecting the density of metals, and .....? Hence, some of these factors are;

1. Concentration of atoms in the metals (closely packed e.g solid or loosely packed e.g gases). This also relates to the mass of the object/metal.

2. Temperature

3. Pressure, etc..

And the 2nd part of the question is well answered by Prof. Walter Lengauer.

1. Does the amount of liquid in which the density of metal piece is being measured also matters?

Yes, the liquid must totally immerse sample and sample holder when sample is added to holder. If sample isn't completely immersed the readings will be more inaccurate.

Water must be 'flat' (i.e no bubbles) and be at ambient temperature - important to measure the temperature of water to get its correct density. I used data from NIST for water density and temperature and use a 5-order polynomial to calculate density and temperature.

If adding fresh water, it is best to leave it a couple of hours to ensure air is out of solution.

2. Does the size of container affects the measured density?

I wouldn't think so providing there is enough water to enable the sample holder to move freely and to ensure total immersion of sample during measurement.

3. Does this method give accurate density calculation for metal piece with weight above 1kg?

In principle, yes but 1kg is rather greater than most laboratory-based balances.

4. What should be the ideal position of metal object in water? Either it should be close to the surface or close to the bottom of container?

Best position is in the middle to ensure that neither sample or holder are touching the bottom or surface.