The Engineer's Place for News and Discussion®

 Previous in Forum: Cast Iron Next in Forum: Positive Pressure Ventilation

### Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

### Rating Vote:

Power-User

Join Date: Oct 2007
Location: Orange County, CA
Posts: 110

### Liquid Volume Measurement Question

01/12/2012 9:32 PM

In our shop we used to use graduated cylinders when making volume measurements of water. We found these measurements to be inaccurate though because the tolerance of the cylinders. We moved to making these volume measurements using one of our precision scales. Since we were just weighing water we weighed in grams for a 1:1 reading in ml's. I have to take some measurements of various liquids now with a range of specific gravity specs. I know that specific gravity is a density or mass of a unit volume measurement and that these numbers usually use water as a reference substance. So my question is this: Let's say that I have a liquid with a specific gravity of 1.2 (this would indicate it's denser and heavier than water - 1.2g/ml), and I pour this liquid into one of my inaccurate cylinders and weigh it. Would dividing the weighed amount (g) by the specific gravity give me an accurate volume? I hope I explained the question well enough to be understood. If not let me know. Also, please correct me if I'm completely wrong in my thinking. Thanks

Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Oct 2008
Location: 34° 34' 21.60" N, 92° 55' 42.28" W
Posts: 20905
#1

### Re: Liquid Volume Measurement Question

01/12/2012 9:46 PM

This will only work at 4°C. And only for water. Then, only if you don't take it out too many places.

__________________
Luck comes and goes. Skill is forever. Intelligence either is, or it ain't. lyn
Guru

Join Date: Dec 2008
Location: Long Island NY
Posts: 6991
#2

### Re: Liquid Volume Measurement Question

01/12/2012 11:22 PM

If you really need high precision volume measurements of fluids then you need a volumetric flask or pipette. A common mistake that people make with graduated cylinders is to measure with the wrong size cylinder. A 100 ml cylinder should not be used to measure 4 ml.

__________________
"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering." Freeman Dyson
3
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 5435
#3

### Re: Liquid Volume Measurement Question

01/12/2012 11:29 PM

You can use the equation, volume = mass/density .Specific gravity is the ratio of the density of a substance (usually at 20 deg C) to the density of water at 4 deg C (1 g / mL)....Density can be calculated using the formula D=Mass/Volume. Volume of a liquid can easily be found using a graduated cylinder.

http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantifying_Nature/Uncertainties_in_Measurements

__________________
The relentless pursuit of pacification....
2
Guru

Join Date: Aug 2005
Posts: 3095
#4

### Re: Liquid Volume Measurement Question

01/13/2012 7:54 AM

I'm a bit perplexed here. Why do you want to measure the exact volume of the liquid. If you need a specific quantity of the liquid: to add to a mixture for example then weighing it will be more accurate because it's independent of temperature.

The procedure you suggest in your original post is correct, but, you need to know the specific gravity of the liquid at the temperature at which you're making the measurement.

__________________
We are alone in the universe, or, we are not. Either way it's incredible... Adapted from R. Buckminster Fuller/Arthur C. Clarke
Power-User

Join Date: Apr 2007
Posts: 414
#7

### Re: Liquid Volume Measurement Question

01/14/2012 12:35 AM

That's correct, and the temperature correction you must apply may not be the same for a solution as for pure water. My most recent copy of the CRC Handbook from the 1950's contains tables of such useful information. There may now be software available that will make those computations and eliminate copying errors.

Power-User

Join Date: Oct 2007
Location: Orange County, CA
Posts: 110
#5

### Re: Liquid Volume Measurement Question

01/13/2012 8:05 AM

Thanks for the responses. It seems most practical then to continue to use the graduated cylinders and specify the margin of error as that of the tolerance of the cylinders. FYI, one of the reasons I wanted to use a scale in this particular case was due to the residual liquid left in the cylinder after pouring it out. It is time consuming to get all the residual out so I figured that by weighing that could be adjusted for by simply taring the scale.

Again, thanks.

Guru

Join Date: Dec 2008
Location: Long Island NY
Posts: 6991
#13

### Re: Liquid Volume Measurement Question

01/14/2012 10:02 AM

I guess you don't realize that a really precise graduated cylinder takes into account the residue left in the cylinder. The volume poured out of the cylinder is what you're measuring. Shaking out every last drop makes your measurement less accurate, not more.

__________________
"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering." Freeman Dyson
Associate

Join Date: Jan 2006
Location: H Town, TX
Posts: 47
#14

### Re: Liquid Volume Measurement Question

01/15/2012 9:58 AM

To add to Redfred, there are cylinders marked TD to dispense and TC to clear.

Guru

Join Date: Apr 2006
Location: Cincinnati, Ohio, USA
Posts: 619
#6

### Re: Liquid Volume Measurement Question

01/13/2012 10:45 PM

The other issue is "What are you doing with the fluid (water or whatever)?"

If you are using it in some form of DEFINED mixture, the BEST measure is mass/weight (of ALL components) because then your mixture will always be and exact percentage of each component.

If you are using volumetric measurements, your will always have to adjust relative to the temperature of the liquid (when it is being measured)- a lot of extra work that can be avoided by weighing the components.

__________________
NO MATTER HOW WELL YOU HAVE DONE SO FAR, ALWAYS TRY TO BE BETTER TOMORROW.
Active Contributor

Join Date: Apr 2006
Posts: 23
#8

### Re: Liquid Volume Measurement Question

01/14/2012 2:34 AM

I agree with most of the others who've written in but i'd like to add two qualifications: First, you can do that conversion with any specific amount of your liquid - or at any given point in the process - but you will be limited in your ability to translate that to a consistent formula or functional relationship, if the cylinder's normal (orthogonal) cross section is varying as it fills. Second, I don't think you can assume that your scale's "tolerance" makes it any better than the cylinder as a measure of mass, taken to mean the number of molecules involved. That is, you say that it's precise, but that doesn't mean it's accurate. Certainly, any scale with a strain gauge is going to have clear limits in that regard (a balance beam type might be more reliable). The question with either of the measuring devices - cylinder or scale - is how well it can track "real" increases in fluid, or, perhaps more aptly put, to what degree either one's readings has a simple linear relationship with the mass of your fluid, in terms of the number of molecules involved.

Commentator

Join Date: Dec 2010
Posts: 61
#9

### Re: Liquid Volume Measurement Question

01/14/2012 3:52 AM

If you said the accuracy you were looking for,I apologize. Specic gravity can vary quite a bit. Temperature, disolved gasses, other impurities,and otherwise insignificant variations in component proportions can make a significant difference in specific gravity. If it a solution you are using, there may be a difference in sg between the top of the storage container and the bottom.

Power-User

Join Date: Aug 2010
Posts: 193
#10

### Re: Liquid Volume Measurement Question

01/14/2012 7:57 AM

Your search for more accuracy in fluid measurement is commendable. However a more complete error analysis is needed. For example, if your specific gravity is only good to two significant digits (decimal), then the graduated cylinders are a better measuring system. As noted above in several posts, there are many different concerns involved. Personally, I prefer weight as a general measure, but that defers to the specific use. If you have an accurate fluid measure, such as a calibrated volumetric flask, you can easily get your specific gravity data on your fluids yourself. Check your data with repeated tests until you are comfortable with your system - if you get really into this (I love it), if would not hurt to do a cost analysis of this whole process. It might turn out that grad cylinders are best after all.:)

Commentator

Join Date: Dec 2010
Posts: 61
#11

### Re: Liquid Volume Measurement Question

01/14/2012 8:57 AM

Actually there are two interelated questions: Is it accurate enough? are you wrong? please define your required accuracy. if the graduated cylindars were not accurate enough for water, they probably would not be accurate enough for the other materials. the question then becomes whether the specific gravity of the other material is accurate enough. The real question may be whether you have the precision you need. Most graduated cylindars are very accurate but with poor precision when they are very wide. Assuming you are using a calibrated digital scale, (?) the precision can be much better than the sight level in the cylindar. If you verify the density of your other fluids, the weight measurement will be better as an estimate of volume. I recommend you first look at the accuracy you need. then look at the acurracy and precision of each of the components in the measurements. you would then answer both of your questions. which really we can't do.

Guru

Join Date: Dec 2008
Location: Long Island NY
Posts: 6991
#12

### Re: Liquid Volume Measurement Question

01/14/2012 9:53 AM

YES!

People so often confuse the real meanings of resolution, precision, accuracy and error. Taking any measurement in one dimension and then converting this into another dimension will always make the final result less accurate than the original measurement. The OP is likely not realizing that the specific gravity of water depends on the temperature of the water, too. So even though a graduated cylinder may not have as much resolution as the digital scale next to it, the uncertainty of the amount of fluid poured out of the cylinder is well defined and requires no additional mathematics. To weigh your fluid and convert this to a volume requires multiple measurements, each with their own uncertainty. In the case of "water" the measurements that affect the specific gravity are the purity of the water and the temperature of the water being measured.

But you are exactly correct that without knowing the process requiring this volumetric measurement, one cannot say what accuracy or precision is actually required.

__________________
"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering." Freeman Dyson
Participant

Join Date: Dec 2011
Posts: 3
#15

### Re: Liquid Volume Measurement Question

01/15/2012 11:02 PM

You will get the correct volume.. Unit of density it self expains the same. density unit is Kg/Lit or g/ml. . If you know density and Kg or g, then you can derive volume i.e. Lit or ml.

Off Topic (Score 5)
Commentator

Join Date: Feb 2007
Location: Gdansk, Poland
Posts: 97
#16

### Re: Liquid Volume Measurement Question

01/19/2012 7:26 AM

If You will use flask with narrow neck, compared to the rest, for example narrow up and wide near bottom (trapezoidal, near triangle, looking from the side), made of quartz glass (less expanding with temperature) , with volume marks on the neck, You can have much better accuracy, then using diagonal cylinder. Accuracy can be 10..100 times better (average cross section/neck cross section) reaching 0.01%. But this is true only when flask is nearly full, when surface of liquid is in narrow part of flask.

Using this type of flask full filled and using enough accurate scale You can determine density. Having density You can use scale for Volume measurement. But density depends on temperature, and may stratify, so mix mixtures and try to make all operations in the same temperature. Good Luck!

Interested in this topic? By joining CR4 you can "subscribe" to