I'm trying to find out what is the inside of a tube could be (like a lab tube) called? Bulb, chamber, reservoir or store? Thanks in advance!

  • I'm trying to imagine a case where I'd need such a word. Pour the liquid into the test tube. Make sure the inside of the test tube is clean. If any residue is left on the inner wall of the test tube... – Jim May 11 '19 at 3:46
  • @Jim yes, I had to think for a minute myself. It's interesting that we do indeed care what the label is for some tubes: if I manage to put a bullet in the barrel rather than the chamber of a rifle, there might be some unintended consequences. – Chappo Hasn't Forgotten Monica May 11 '19 at 4:23
  • @Chappo - Yes, but that's a rifle. This specifically for a test tube. – Jim May 11 '19 at 7:11
  • I might say "interior". – Hot Licks May 12 '19 at 12:03

In the body, the inside of a tubular structure is called a lumen. This would apply to blood vessels and the stomach, but not the oral cavity, cranial vault, or upper chambers of the heart. The upper chambers are more definitively called atria (lat: rooms) while the lower chambers are ventricles (diminutive of venter (“belly, stomach, womb”)). I wouldn't hesitate to use the word lumen for the inside of a straw or a test tube, but might risk not being understood. So many great words for the insides of stuff! Lumen also refers to the International System of Units designation for a parcel of luminous flux.


It's just "the tube" or "the inside of the tube" in my opinion. There isn't a specific word for the inside of other simple vessels or containers like bottles, jars, cups, beakers or even closed containers like barrels or tanks. You only need a word when the object has more than one space inside it.

For instance a sand glass like an egg timer has two connected spaces and you might refer to sand flowing from the upper chamber to the lower chamber and the two chambers being reversed to continue timing.

I would refer to "the bowl" of a stemmed wine glass because the stem and base are other parts of the glass but I wouldn't talk about "the bowl" of a tumbler or highball glass because there are no other parts from which to distinguish it. A tumbler is a tumbler. It has a rim, a bottom, sides, an outside and an inside. The same applies to a test tube or boiling tube.


This is the chamber of the test tube.

See Definition #2 of the Merriam Webster Dictionary’s entry:

A natural or artificial enclosed space or cavity

  • If you look below the picture 'inner chamber' refers to what the test tube fits into. "Replacement test tube for the LaMotte 1060 Water Sampler (sold separately) Fits the inner chamber of the sampler". – Nigel J May 11 '19 at 0:35
  • 1
    @NigelJ Dang, you are right. A bit of confirmation bias there. It’s still the word I would use but I will look for a better justification. – James McLeod May 11 '19 at 0:56

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