"Liquid Silver" Can Tarnish Life

By Joe Schwarcz PhD, Author, USASEF Expo Performer, AT&T Sponsored Nifty Fifty Program Speaker
Physicians today are unlikely to encounter "Gilder's palsy." Nor are they likely to diagnose a patient with "hatter's shakes." But prior to the twentieth century these ailments had to be considered when a patient presented with tremors, irritability, increased salivation and fatigue. In the case of the hatters, the culprit was mercury nitrate used to produce felt. Beaver and rabbit fur, the traditional materials for making felt, can be matted more easily when the pelts are first treated with mercury nitrate, a chemical that opens up the pine cone-like layers known as "imbrications" on the surface of individual hairs. When these are opened up, adjacent hairs can interlock more readily. Hatters invariably got the mercury nitrate on their hands and since their hygiene was probably less than exemplary, ended up ingesting some of the toxin.

Mercury's toxicity is a consequence of its ready binding to sulphur, an element that is a crucial component of many enzymes. Some of these enzymes are critical to the workings of the central nervous system and their failure to function properly when bound to mercury causes the shakes and mental disturbances that are characteristic of mercury poisoning.

Gilders, whose profession was based on coating metal objects with gold, exhibited symptoms similar to that of hatters. Their problems, however, came not from exposure to compounds of mercury, but from exposure to metallic mercury, the silvery liquid found in thermometers. The Romans called the metal hydrargyrum, meaning "liquid silver." That also explains why we use the symbol Hg for the element. Unlike mercury nitrate, liquid mercury is somewhat volatile and can therefore be inhaled and absorbed into the bloodstream from the lungs.

Metallic mercury does not occur in nature, but it can be produced by heating cinnabar, a naturally occurring form of mercury sulphide (HgS). The metal has long fascinated people, especially the alchemists who thought that it was the key to the transmutation of base metals into gold. Of course it was not that, but there is a gold connection. Gold readily forms an alloy with mercury, a phenomenon that is apparent to anyone who has handled mercury while wearing a gold ring. While playing with mercury is a bad idea, the historical alloying with mercury to form "gold amalgam" has been an important method for isolating gold from ores. The traditional process involves crushing the gold ore, mixing it with mercury and separating the amalgam that forms. This is then heated to drive off the volatile mercury, leaving pure gold behind. But it can leave something else behind as well. The misery of mercury poisoning! And many a button gilder could have testified to that.

Military uniforms commonly feature golden buttons. Until about the middle 1800s these were made by dipping metal buttons into gold amalgam and then heating to evaporate the mercury. The layer of gold left behind was very thin, just one gram of gold was enough to gild about 500 buttons. The results for the buttons were pretty, but for humans, not so much. On occasion, even construction workers had to deal with "gilder's palsy." About 100 kilos of gold were mixed with mercury for application to the copper sheets that were used to create the golden dome that adorns the cathedral of St. Isaac in St. Petersburg. The dome, unfortunately, is also a symbol of mercury poisoning. Some sixty workers died as a result of mercury inhalation! However, the chemical ingenuity of two Italians would eventually put gilder's palsy on the back burner.

In 1800 Allisandro Volta's discovery of an electric current flowing between two dissimilar metals separated by moistened cardboard established the chemical principles that would lead to the first battery. Just five years later his friend, Luigi Brugnatelli reported in Belgian Journal of Physics and Chemistry how he had put the "Voltaic pile" to use: "I have lately gilt in a complete manner two large silver medals, by bringing them into communication by means of a steel wire, with a negative pole of a voltaic pile, and keeping them one after the other immersed in ammoniuret of gold newly made and well saturated." Brugnatelli had discovered electroplating, a process that would be commercialized by Henry and George Elkington of Birmingham, England in 1840.

The elimination of gilder's palsy thanks to electroplating did not mean that we were rid of poisoning from inhaled mercury. Consider the case of the 68 year old man and his 88 year old mother in law in Michigan who were admitted to hospital with nausea, diarrhea and vomiting. The next day, the man's son and daughter in law were brought in with the same symptoms. Because the esophagus and lungs of all four were inflamed, doctors suspected chemical exposure. It turned out that the son worked for a company that manufactured dental amalgam which is an alloy of mercury and metals, mostly silver. With the price of silver on the up and up, he had the bright idea of stealing some of the material and extracting the silver by evaporating off the mercury. Thinking he had a formula for riches, the prospective alchemist set up a crude lab in the basement equipped with a furnace for melting metal. He had a formula alright, but it was one for disaster. Despite the use of dimercaprol, a drug that can bind to mercury through its sulphur atoms, all four mercury poisoning victims died. Their house was demolished and the debris treated as hazardous waste.

You don't have to be a greedy crook to suffer from mercury inhalation. You can be an inquisitive youngster. Like the boy who dissected a household thermostat and spilled the mercury on the carpet. He vacuumed it up but never changed the bag. With each subsequent use of the vacuum cleaner some of the mercury vapourized. Months later the boy was hospitalized with weakness, weight loss, anorexia, lethargy and insomnia. Luckily in this case dimercaprol treatment was effective. Too bad Alice didn't have any to offer the Mad Hatter.