A graduated cylinder is basically a test tube with volume markings. It has a spout for pouring and a built-in base so it can stand upright on its own. They measure volumes accurately if the reading technique is correct. The video below helps demonstrate this.
What is a Meniscus?
A meniscus occurs between a liquid and the air above. It always forms with a downward-facing curve whether it is coffee, milk, scotch or water. You can see it in narrow vessels such as test tubes and graduated cylinders. It is not as apparent in a larger container such as a bucket. Water has a much higher surface tension than other liquids such as alcohol and produces a much more pronounced meniscus.
Graduated cylinders can measure volumes of liquid accurately. Indigo Class B cylinders are rated at 1% accuracy if read properly and is shown in the video below.
The bottom of the meniscus should line up with the cylinder’s calibration lines for an accurate reading. The video shows a 100 ml graduated cylinder in use where the viewing angle is level. This is compared to reading slightly above and below which is wrong.
This technique also makes measuring the volume of irregular solid objects possible. Imagine you have a 50ml measuring cup filled with sand that is level at the top. How much of the 50ml is air and how much is sand?
An easy way to find out is to fill the 100ml graduated cylinder exactly halfway, i.e. to the 50ml line. Then pour the sand in. If there were no air, it would fill the graduated cylinder to the 100ml line. But, because there is air, the water and sand should raise the level to 90 or 95ml? Try this with very coarse and very fine sand.
We’ll explore this application in another blog & video.