While volumetric measurements are used in countless applications on any given day, perhaps the ones that most directly affect us on the reg are cooking measurements. One cup of this, two tablespoons of that, half a cup of the other…a mismeasurement on any part of a recipe can significantly alter the resulting meal. A mix up might yield delicious results, or it might make your favorite dish nigh unpalatable.
With measurements being such an important part of cooking, it’s good to know that the standards for volume are so absolute. Or are they?
Measuring A Measurement
For this demonstration, you’ll need a fairly large glass jar, three divided cups of water (as in, three individual cups of water—eight ounces each), one cup of sugar (also eight ounces), masking tape, a writing utensil, and a spoon.
First, affix a strip of masking tape to the outside of the jar, vertically. Next, pour one of your three cups of water into the jar and mark the tape with a horizontal line and a “1” to indicate its level. Pour in the second cup of water and mark the level with a line again, adding a “2” this time. Water a plant or something like that with the water in the jar, then dry the jar thoroughly.
Pour the cup of sugar into the jar; it should reach the “1” mark on the tape—if not, fudge it a little bit by adding more (or subtracting, if necessary). Then, pour in the final cup of water and gently stir the jar with your spoon.
In theory, one cup of sugar plus one cup of water, equaling two cups, should reach the same height as two cups of water. But, as you’ll notice, it comes up short. To where did that missing volume disappear?
What Gives, Mr. Science Demonstrator Man?
The difference in volume is due to the structure of sugar. Because it is not a uniform solid throughout, but rather thousands of individual granules that don’t quite match up perfectly on all sides, there are innumerable miniscule spaces between the granules. Upon stirring the sugar and water together, the water rapidly moves into these voids, resulting in an apparent loss of volume. (This process would also occur without stirring, but it would take far longer and the results would not be quite as dramatic.)
Water is a liquid; sugar is a solid (despite the seeming fluidity of sugar crystals); the air between the sugar granules is a gas. These three different types of matter cannot occupy the same space at the same time. As such, the water “moves” the air out from between the sugar crystals and takes its place.
- Janice VanCleave’s 201 Awesome, Magical, Bizarre, and Incredible Experiments, Janice VanCleave, 1994. ISBN 978-0471310112