Like most science and technology enthusiasts, I’m fascinated by chemical elements. The best website in the world for exploring real-world elemental examples is Theodore Gray’s Periodic Table.
Part of Theodore’s collection consists of metal samples that provide a unique sensory experience when picked up. Specifically, you'll be astonished by the difference when you physically compare the weight of two equally-sized cylinders of magnesium and tungsten.
Three cylinders demonstrating the differences in density of elemental magnesium, aluminum, and tungsten.
Tungsten, is one of the densest natural elements; much heavier than mercury and lead for the same volume. Tungsten has nearly the same density of gold, but with a much lower price. Tungsten carbide is commonly used in sharp tools, such as end mills and drills. Small tungsten weights and putty are sold online to insert into Pinewood Derby Cars.
Magnesium, on the other hand, is one of the least dense natural elements. Lithium and sodium are much less dense, but are so reactive that they need to be kept in oil. Similarly, magnesium strips are sold as fire starters and provide brilliant white light in fireworks. Structurally, for its combination of strength and light weight, magnesium is used in racing cars and high-end sport car parts, as well as mobile, tablet, and laptop cases.
For comparison, I include aluminum in my cylinder samples, as people are familiar with it as a common lightweight metal.
|Element||Mass (g)||Height (mm)||Diameter (mm)||Volume (mm3)||Normalized Mass (mm3)||Measured Density (kg/m3)||Reference Density (kg/m3)|
Dimensions and weight of sample cylinders.
Examining the table above, you'll notice that tungsten is ten times denser than magnesium. The measured density compares favorably to the published density of the pure elements.
My tungsten sample came from eBay, sold by “rgbco”.
Narrower tarnished magnesium
cylinder on top of newly-machined
I purchased a magnesium cylinder at the same time. Sadly, that cylinder turned out to have a slightly smaller diameter. (Matching cylinders are now available.)
The size difference detracted from the experience of comparing the weight of the samples. I didn’t like explaining to people that the magnesium cylinder was close enough, and that the slightly smaller size wasn’t some cheap trick to enhance an illusion. So, I decided that I needed to make matching cylinders.
Because tungsten is very difficult to machine, I wasn’t going to try to attach it to my lathe and reduce the diameter. However, pure magnesium is available, it isn’t too costly, and is machinable. I decided to replace the smaller-diameter sample (pictured on top) with a correctly-sized sample (bottom) that I machined myself.
I couldn’t find magnesium rods from any of my favorite metal supply retailers. At the time, I couldn’t locate any rods that were large enough even on eBay. The nearest I could find was a large metal ingot the size of a loaf of bread.
How can I transform a large rectangular block into a cylinder? Turn to the next page to find out.