Does Hydrometer test tube size matter?

Heyas all,

I broke my hydro a few back. I ordered a new one from AHB, but just the glass hydro. I figured I could use my old test tube (from NB) and it would float the same.

I tested my hew hydro in tap and bottled water at 60 degress. it seems to be .004 off.

SO does the the size of my test vessel matter enough to throw off my hydro?

ty!


PS. The first hydro I bought arrived broken, but I emailed AHB and they shipped one on the next day! :rockin: great guest service.

 

As long as the tube is big enough to hold the hydro, any size is fine.
Take a look at your hydro and see if it's calibrated for a different temp. Most, but not all, are calibrated for 60 degrees. If yours is standard, then just adjust by 0.004 SG. If you're up for the hassle, it might be worth your time to test a known concentration of sugar water, too, just so you know a proper adjustment factor at, say, 1.050 SG.

Of course, there's always option 3: RDWHAHB

 

You know how barges have lines on their hulls painted to show how much cargo they are carrying? The boats will float just as deep whether they're in a pond or the middle of the Pacific. Same principle applies here.

 

Unless the pond is full of sugar! Then it'll float higher :rockin:

 

just make sure no bubbles are sticking to it and giving it false buoyancy, although I'm in the same boat, mine read .004 off in a tube of water the other day, dono what to do about it.

 

If you really want to make sure you're doing the right test, use distilled water and make sure that you're using the closest thing that you've got to a properly calibrated thermometer. If the temp is off, your readings will also be off.

 

You used tap water to test it? In order to calibrate it you use distilled/

 

well I knew to use distilled, but I figured that there was no way the difference with tap water was gonna be .004

 

Actually it says, I tried both just to check it out, and i used a glass and metal thermo......

thanks for the replies!

 

Actually, for the record, the size of the vessel does matter if the clearance between the wall and the hydrometer is small enough to create a capillary action (this can even occur when the bulb of the hydrometer is beneath the surface):

http://en.wikipedia.org/wiki/Capillary_action

But, it would have to be a pretty tight fit for that to happen - I doubt that's what the .004 discrepancy is from.

 

What was the purpose of this post? It literally adds nothing to the discussion, since the capillary effect is negligible for tube widths over a centimeter or so. Even if it did rise substantially, it wouldn't affect the reading, because you read a hydrometer from the bottom of the meniscus.

If you're going to jump in with a "for the record" statement, you might want to make sure that it's 1) accurate and 2) not referencing wikipedia in defiance of common sense.

 

Giving the Hydro a quick spin in the wort sample will draw off any bubbles if present...

 

If the pond is full of beer, it'll float higher still, since the entire crew just jumped in for a drink!

 

Perhaps capillary effect is not the correct term (it escapes me), but trust me, the same situation would occur around the BULB of the hydrometer (as in the fat part). If the clearance between the vessel and the BULB of the hydrometer is small enough, there will be a "capillary effect" (or whatever the correct term would be) BENEATH the surface, surrounding the bulb, that will drive the hydrometer up in reference to the surface (the bottom of the meniscus, as you care to specify).

Since the poster did not specify either the size of his hydrometer or vessel, it is possible - my hydrometer test jar has a pretty small diameter, but so does my hydrometer. If it was much larger, as I've seen hydrometers, it is very possible.

Don't believe me? Try sticking your hydrometer in a vessel with a small clearance around the edges (I'd guess less than 1/16") and see if reads the same as in a large container. It won't.

P.S. MS of Mechanical Engineering with a concentration in fluid sciences and heat transfer.

 

Challenge accepted, sir.

It just so happens that I have a hydrometer storage tube that barely fits the hydrometer. There is less than 1/8 inch of clearance. The storage tube is plastic, which might affect the capillary action, but there is still a meniscus.

I used two different hydrometers to measure the specific gravity of distilled water in both a "normal" hydro tube and in my super-skinny tube.

Hydro #1:
Skinny tube = 1.0025
Fat tube = 1.0025

Hydro #2:
Skinny tube = 1.0010
fat tube = 1.0010

If there's a difference, it's not discernible by the naked eye (and I'm excessively familiar with analytic glassware).

P.S: Physics education, plus a healthy dose of trying things myself instead of citing a book or maybe wikipedia. I took a fluids class once, but I don't remember learning much. We mostly applied physics.

 

Oh, its on. ;-)

 

Well, like I said, it probably won't have an effect unless smaller than 1/16" clearance, but that's just a guess. My hydrometer test jar that I use on a regular basis has about 1/8" clearance.

If I had a skinnier tube or a fatter hydrometer, I'd test it myself.

All of my fluid books are at work - if I've got a few spare minutes tomorrow I'll see if I can't find the correct term or "borrow" a test tube (don't tell my boss). It's mainly just a function of viscosity. If you don't mind putting cold motor oil in your hydrometer tube (I do), the effect should be multiplied.

 

It's less than 1/8" clearance. If capillary action was affecting it in a non-negligible way, that's little enough clearance to see the effect (since capillary action depends directly on the width of the fluid layer). It's a moot point in any case, since I can't think of a reason you'd do a hydro test in a vessel that is actually smaller than the storage tube, and there is no noticeable effect at that scale.

I'd appreciate it if you can find the topic. I don't want to come across rejecting the idea out of hand- I just don't think that there's any effect on a noticeable scale.

 

Like hell it will, the pacific is salt water ponds are fresh water, salt water has a higher buoyancy.

 

Well, there you have it... Just like the old adage, size DOES matter. You heard it here first folks.

 

Well, I guess we heard it in February. Almost two years ago