Liquid Metal: The Fascinating Properties of Wood’s Metal
| Polish version is here |
The beauty of exploring science and the laws that govern our world lies in the fact that inspiration can be found in the most unexpected circumstances. Many of history’s great discoveries stemmed from curiosity about seemingly trivial matters. Today, let’s take a moment to consider metals.
If we examine the periodic table of elements, we will notice that the vast majority of elements are metals. Metals are abundant in nature and continue to form the foundation of modern technology and industry. We know and use many different metals and their alloys. These elements share a set of common properties, including their characteristic luster, ductility, malleability, and excellent thermal and electrical conductivity.
Surprisingly, inspiration for this topic can even be drawn from literature, such as Prus’s novel The Doll.
Geist did not remove his gaze from him, but he gradually calmed down. Finally he exclaimed:
'Come over here, to the table. Look, what is this?’ […]
Wokulski gazed in turn at the metal heavier than platinum, at the transparent metal, at the metal lighter than fluff. As long as he was holding them, they seemed to him the most natural things under the sun: for what is more natural than an object which acts upon the mind? But when he gave the samples back to Geist, amazement overcame him as well as incredulity, wonder and alarm. So he inspected them again, shook his head, believed and doubted by turns.
In this passage, the protagonist marvels at the properties of metals created by the brilliant chemist Geist, whose mind is consumed by the idea of producing a metal lighter than air. Since the novel’s publication, scientists have indeed discovered metals heavier than platinum, such as uranium and plutonium, but the concept of a metal lighter than air remains an unfulfilled fantasy.
However, there are metallic substances with properties that significantly deviate from what we might expect. One such material is Wood’s metal.
We are accustomed to thinking of most metals as hard, durable solids under normal conditions. The only naturally liquid metal is mercury, but its high toxicity discourages experimentation. Gallium melts at just 29.76°C (85.57°F), but its high cost makes it impractical for many applications.
In addition to pure metals, we also classify their alloys. A particularly intriguing example is Wood’s metal, which has the surprising property of melting at a temperature lower than the boiling point of water. As a result, it melts in hot water and behaves similarly to mercury.
Preparing this material in a home laboratory is not difficult.
Preparation and Observations
To synthesize this alloy on your own, you will need the following metals:
- Lead Pb,
- Bismuth Bi,
- Tin Sn,
- Cadmium Cd.
Warning: Lead and cadmium are highly toxic! Exposure to these metals should be minimized, and direct skin contact should be avoided. Heating these metals or their alloys must be done under a fume hood or outdoors! The author assumes no responsibility for any potential harm. You proceed at your own risk!
The most interesting component in this alloy is bismuth. It is the heaviest non-radioactive element. Technically, all bismuth isotopes are radioactive, but their half-lives are so incredibly long that decay is negligible. For example, the half-life of 209Bi is estimated at 1.9 × 1019 years—at least a billion times the estimated age of the universe. This means that half of the atoms in a sample of bismuth would take that long to decay.
Bismuth is also visually striking—it has a beautiful metallic sheen with a pinkish hue:
The melting point of bismuth is 271°C (519.8°F). One of its remarkable properties is its ability to lower the melting point of alloys in which it is incorporated. Wood’s metal can have varying compositions, but bismuth is always their main component.
The lowest melting point is achieved with the following composition (by mass percentage):
- 24.9% Pb
- 50.1% Bi
- 14.6% Sn
- 10.4% Cd
This particular Wood’s metal melts at just 65.5°C (149.9°F).
How do we prepare the alloy? First, weigh out the required amounts of each metal. Then, melt them together in a ceramic crucible, making sure it is covered to reduce oxidation. Lead should be melted first, followed by bismuth, tin, and finally cadmium. The molten alloy should be stirred with a thick steel wire and then left to cool.
Wood’s metal can easily be cast into desired shapes. The sample I prepared was shaped into convenient rods (one of which is shown below) by casting it into a mold made of… plastic.
The behavior of this material can be seen in my video:
Wood’s metal is not just a curiosity—it has numerous practical applications:
- As a solder in jewelry making,
- As a fusible element in fire safety devices,
- As radiation shielding material for X-rays,
- As a medium in laboratory heating baths.
Dear reader, I believe you will agree that witnessing a metal transition into a liquid at the temperature of hot tea is truly fascinating.
Enjoy your experiments! :)
Further readings:
- Birchon D., Dictionary of Metallurgy, Philosophical Library, London, 1965
- Sękowski S., Pierwiastki w moim laboratorium, Wydawnictwa Szkolne i Pedagogiczne, Warszawa, 1989, pp. 59-61.
Marek Ples