When ordering a diet soda (no sugar soda) in a cafe or restaurant I would like to be sure I am getting a diet soda and not a regular sugar-infested soda. Because a regular soda, is through all the sugar, far more dense than a diet soda, my idea is to use a simple hydrometer. Ideally this hydrometer would be a simple everyday item that sinks in diet soda but floats in regular soda. I already tested this this idea with some simple items such as coins or small toys. However all tested items either sink in both cases or float in both cases. Anybody has a good idea for a suitable item that sinks in diet soda but floats in regular soda ?

UPDATE although it didn't really answer my question, the experiment suggested by matt_black was too simple not to try out. However what happened when I performed the experiment was that both the can of regular coke and zero coke sank. I discovered there are a lot of video's on youtube showing a can of diet coke floating and only the can of regular coke sinking. So I am quite surprised by my own findings.

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    $\begingroup$ How about a capsule containing the sugary stuff - the enclosing material should ideally have a density in the range of the two solutions' densities, and the capsule would have to be free of air. It's an interesting idea but sounds like a mess. Aren't your taste buds good enough? $\endgroup$
    – Buck Thorn
    Commented Sep 1, 2019 at 19:31
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    $\begingroup$ Saccharometer. Also, if all you want is to quantitatively distinguish between two glasses of coke, something primitive like a plastic straw with a small blob of chewing gum on one end would also do. Just make sure it freely floats in your sugar juice. Alternatively, you can borrow a set of areometers from a friend who does some home brewing:) $\endgroup$
    – andselisk
    Commented Sep 1, 2019 at 19:32
  • $\begingroup$ Won't the dissolved CO2 affect the density? $\endgroup$ Commented Sep 1, 2019 at 21:45
  • $\begingroup$ Unopened cans of Diet Coke float in water. Sugary cans sink. You don't need anything more complex. $\endgroup$
    – matt_black
    Commented Sep 2, 2019 at 15:36
  • $\begingroup$ @matt_black, a simple test indeed and I will definitely try it out. However I can't use it to test a served drink in a glass. $\endgroup$ Commented Sep 2, 2019 at 16:02

2 Answers 2


Better than a hydrometer, use an Abbe refractometer to measure the index of refraction, which varies with sugar concentration. It requires just a drop of liquid, and that small sample is unlikely to have bubbles, reducing density. You can make a refractometer to measure the sugar concentration, or you can buy one for ~$US20.

That said, diet sodas have been linked to a number of health issues, such as diabetes and diabetic retinopathy. You might be better off with unsweetened products such as seltzer, club soda, tonic water or two cents plain.

On the other hand, if you want to explore brewing or candy making, that refractometer could be useful...

À votre santé!

  • $\begingroup$ Those supposed health risks from diet drinks are poor quality nonsense, especially so since they usually don't compare risks to the consumption of very sugary drinks. You really should not promote them until someone does a s study with decent scientific respectability and doesn't exaggerate the implications. $\endgroup$
    – matt_black
    Commented Sep 2, 2019 at 15:40
  • $\begingroup$ @matt_black, seltzer and other bubbly drinks mentioned above are just carbonated water, without any "health benefits" or artificial sweeteners. They could cause gas pains, if consumed in excess, though ;-) $\endgroup$ Commented Sep 2, 2019 at 19:07

The refractometer is an elegant solution, indeed.

Other option is to use a simple, home made, small container with water tight cap, with adjusted mass of e.g. fine sand or salt content to have container average density between both colas.

You would adjust it to sink in diet cola and float in regular cola.

Note that I am not a cola drinker,but I guess there is a reduced sugar cola as well. So perhaps reduced sugar cola should be used instead of regular cola. Or you can have 2 such devices to distinguish all 3 kinds of cola.


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