Why were alchemists trying to get gold particularly from mercury?

Question

This question is on chemistry/physics/history.

The first (and arguably the easiest) nuclear transmutation producing gold involved mercury, its neighbor in the periodic table.

Obtaining gold from other metals, without access to nuclear technologies, by purely chemical means, is equally hopeless, independently of which starting ingredients are chosen.

And yet, for hundreds if not thousands of years, it has been mercury who was typically considered as a major ingredient for such attempts. It it a mere coincidence? Or is it because mercury has such weird properties (liquid at room temperature, poisonous) that it kinda makes sense to use it as a starting point for obtaining other metals, including gold? Do mercury and gold have any similar chemical properties? (which could have been observed in ancient times, leading to a conclusion that such a transmutation is possible)

Answer 1

Although there are some good answers, I will mainly focus on the historical aspect.

Elemental mercury was known to the ancient Greeks, Romans, Chinese and Hindus and in the theory of alchemy, mercury was considered as one of the three principal substance (other being sulfur and salt) and every metal was made of these three principal substance in different ratios. However, the alchemists considered gold as the most perfect metal and other metals as "sick". So, they wanted to "cure"(convert) every metal to gold particularly mercury. Below are some excerpts from some articles:

Alchemy is a pre-scientific field of study that was widespread up until the Middle Ages, and focused on the nature of materials and the reactions between them. Alchemy combined philosophical beliefs, like the belief held by Greek philosopher Aristotle, according to which every material in nature strives for perfection. The most perfect material, according to alchemists, was gold. Besides its unique color, gold can withstand other materials and environments, and it is easy to weld and shape. Alchemists thought, like Aristotle, that other materials, such as lead and iron, are inferior and "sick" They believed these could be "cured" and turned into the coveted gold in a process called "transmutation".

_{https://davidson.weizmann.ac.il/en/online/orderoutofchaos/can-lead-be-turned-gold}

In the ancient art of alchemy, mercury, sulfur, and salt were the Earth’s three principle substances. The Hindu word for alchemy is "Rasasiddhi", meaning "knowledge of mercury". Believing that mercury was at the core of all metals, alchemists supposed that gold, silver, copper, tin, lead and iron were all mixtures of mercury and other substances. While alchemists in different cultures had different beliefs, one of the central themes to European alchemy was the belief that the correct combination of mercury and other ingredients would yield riches of gold.

_{https://sites.dartmouth.edu/toxmetal/mercury/mercury-element-of-the-ancients/}

You can go also go through the below links articles for an indepth discussion on this topic.

1. Simioli, Carmen. "Alchemical Gold and the Pursuit of the Mercurial Elixir", Asian Medicine 8, 1 (2013): 41-74, DOI: 10.1163/15734218-12341289
2. https://timesofindia.indiatimes.com/home/sunday-times/deep-focus/the-curious-case-of-an-experiment-with-alchemy/articleshow/3089537.cms

Answer 2

Good question. Here is a SWAG. Well, maybe not so scientific.

1. Gold (Au) is exceedingly dense, ~19 g/cm³, as is mercury (Hg), ~14 g/cm³, and lead (Pb) floats on Hg.

2. Both Au and Hg are highly reflective, but Pb quickly dulls.

3. Au is soft as butter, and the alchemists knew how to make it into sheets 100 nm thin. (One can continue the process until the gold is a transparent greenish, useful for filters but not for gilding.) Mercury is not merely soft, but liquid.

4. What might have been the biggest red herring is that Hg dropped onto Au dissolves into it in seconds (as I found when I got some on a ring)! At first, the Hg leaves a silvery-colored stain... but in a matter of days, the stain disappears, leaving apparently unadulterated gold (as I also found... BTW, the amalgam is safe, not releasing Hg vapor).

   Using Archimedes' method to check purity of Au can fairly easily show if Au is adulterated with less dense Ag, ~10 g/cm³, but the more-dense Hg could be added in small amounts, appearing to increase the weight of gold without a *perceptible8 decrease in density.

   A mountebank would think, "Eureka! Drop some mercury on gold, wait a few days, and I've made gold from mercury"... until some wise-guy heats the gold, distilling off the Hg (and slowly poisoning all in the assay office).

Answer 3

I will give a naive and personal answer without any source, this question surely belongs to another SE site, I don't know much about alchemy, the use of mercury could be related to their ideology and a financial reason even if this attempt is totally absurd.

If the process of obtaining heavy elements in supernova nucleosynthesis would have required a significant amount of energy, some of them are really abundant on earth compared to light elements and are very cheap. There is a wiki table giving the Price and abundance of chemical elements (an approximate value can be interpolated for the price in the past). Lead is one of the cheapest and is an abondant element in the row containing gold. Pb is literally is inferior and a best choice to be transformed into gold. Nowadays the position of Pb itself three steps away from gold in the table might also be the reason of this choice. The transmutation of lead into gold was certainly a challenge. A wiser process will be to make a transmutation of another cheaper element very close to gold for an easier and historic transmutation. If this is achieved, a series of transmutations can be made Pb $\rightarrow$ Tl $\rightarrow$ Hg $\rightarrow$ Au. It's the likely explanation for this choice.

There is certainly another way to say left to right, but Os, Ir and Platinum are rare and expensive, such a success wouldn't make much difference, which explains the right-to-left tendency (heavy to lighter elements) in the transmutation process. At least if they'd known about another similar quasi alchemical process : cold fusion, they might have tried it with light metals.