# B Can color be used for measuring density?

#### Isolde Wilde

I am wondering if can the colour of a liquid be related to its density?

Related Classical Physics News on Phys.org

#### Ibix

Not simply. Otherwise liquids would change colour when heated. It has more to do with the structure of the electron orbitals of the molecules of the liquid.

#### ZapperZ

Staff Emeritus
2018 Award
I am wondering if can the colour of a liquid be related to its density?
This can't possibly come out of nowhere. What makes you think color has anything to do with a liquid's density?

Zz.

#### DrClaude

Mentor
For specific colored solutions, there is a relation between color and concentration, so one could infer the density of the result (with proper calibration).

But in general, as the others have said, there is no link between the two.

Amongst other things you could look at trends in the properties of the elements. With the halogens, for example, as you move down the group the densities increase and the colours get darker. But are there similar trends when all the halogens are in the liquid state? Google should help.

#### ZapperZ

Staff Emeritus
2018 Award
Amongst other things you could look at trends in the properties of the elements. With the halogens, for example, as you move down the group the densities increase and the colours get darker. But are there similar trends when all the halogens are in the liquid state? Google should help.
But even if this is true, it isn't universal, as exemplified by water at various temperatures. We certainly know that it's volume changes (and thus its density) from 0 C all the way to 100 C. Yet, its "color" does not change!

So whatever principle or rules that one comes up with is spectacularly falsified by water!

Zz.

Gold Member
For specific colored solutions, there is a relation between color and concentration, so one could infer the density of the result (with proper calibration).

But in general, as the others have said, there is no link between the two.
This is important to emphasize. Across multiple different liquids, this wouldn't work, but for one specific liquid, it could depending on the situation.

A similar idea is used with gases quite frequently in a process called laser-induced fluorescence. It's not a one-to-one comparison, but the idea is that you either have a suitable gas already or you seed the gas with small quantity of another gas that fluoresces when exposed to a specific wavelength of light, then expose it to that wavelength with a laser. The brightness of the fluorescence can be correlated to density, concentration, temperature, and sometimes other quantities depending on the assumptions made and the experimental setup.

But even if this is true, it isn't universal, as exemplified by water at various temperatures. We certainly know that it's volume changes (and thus its density) from 0 C all the way to 100 C. Yet, its "color" does not change!

So whatever principle or rules that one comes up with is spectacularly falsified by water!

Zz.
I have no idea at all whether there is a relationship between liquid density and colour but I think it's an interesting project to do some research on. The colour of water might not seem to change with temperature but its refractive index does.

#### A.T.

So whatever principle or rules that one comes up with is spectacularly falsified by water!
I agree regarding the rule proposed here, but water is always the exception anyway:

#### pinball1970

Gold Member
I am wondering if can the colour of a liquid be related to its density?
Ive read all the comments and there has been no mention of optical density specifically although Dr Claude may have had this in mind in post #4.
We use to use this to see how turbid a liquor was, a vial was placed in a spectrophotometer and one could glean calculate various things from the readings.
Colour (of a sort) came into it when we were checking dye liquor but from memory these were not true solutions although they were coloured with soluble reactive dyes.
There are more sophisticated applications for measurements in biochemical and microbiological techniques.

#### ZapperZ

Staff Emeritus
2018 Award
I agree regarding the rule proposed here, but water is always the exception anyway:
It isn't. Look at mercury that was used for a long time in thermometers. Do you see it changing colors as it expands or contracts with varying temperatures?

Zz.

#### A.T.

It isn't. Look at mercury that was used for a long time in thermometers. Do you see it changing colors as it expands or contracts with varying temperatures?
As I said, I agree about the colors.

### Want to reply to this thread?

"Can color be used for measuring density?"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving