The phrase 'mad as a hatter' is in common English usage but its origin is not so well known. It is derived from the workers who used mercury in the preparation of felt for hats. Beaver and rabbit fur, which were used to make the felt hats, were treated with mercuric nitrate, a mercury salt, in order to matt the fur together, a process called carroting. After this process, the fur would be heated and the workers inevitably became exposed to mercury vapour. The symptoms developed by the workers became well characterized from observations of groups of workers in the industry. These consisted of tremors ('hatter's shakes'), mental disturbances ('mercury madness'), a jerky walk, stammering speech, and apparent pathological shyness.
Elemental mercury, which is a liquid, is found in the free state in rocks, for example the mercury mines in Slovenia and Spain. It was known as quicksilver and its Latin name, hydragyrum (from which its chemical symbol, Hg, is derived), means liquid silver. It is also found combined with sulphur in brightly coloured cinnabar, and with oxygen.
Liquid mercury was certainly known in 1600 bc in Egypt and probably also in China and India. Compounds of mercury such as cinnabar have been mined for more than 2,500 years in Spain, and it was known from around ad 300 that heating this produced metallic mercury. Mercury has been used in various ways for centuries and its use has often been associated with toxic effects. The Greeks and the Romans knew it was poisonous. Apart from the felt-making industry, exposure to mercury would have occurred in the mines where the metallic mercury was found. Mercury was later used extensively in scientific instruments such as barometers and thermometers. The alchemists used mercury in a vain effort to turn base metals into gold, and it is believed that King Charles II died of mercury poisoning as a result of his dabbling in alchemy.
One of the unusual properties of mercury is that it reacts with certain other metals to form amalgams. Amalgams of silver and tin became used for filling cavities in teeth in the nineteenth century and similar amalgams were used until very recently. This ability to form amalgams has also been utilized in the extraction of metals like gold and in plating. Thus amalgams of gold and mercury could be used to deposit or to plate gold onto other surfaces such as buttons. The process led to mercury vapour being released and the workers becoming poisoned, suffering from 'gilder's palsy'. The waste mercury also poisoned those living near the factories. It was reported that sixty Russian workers died as a result of exposure to
mercury when gilding the dome of St Isaac's cathedral in St Petersburg. Similarly, the making of mirrors involved using a silver amalgam, which also exposed the workers to mercury. A more bizarre case of mercury poisoning occurred when the liquid metal was being transported by ship in i8i0. One of the flasks containing the mercury broke open during a storm, with the result that three of the crew died of mercury poisoning.
Various forms of mercury have more recently been used in industrial processes: as an electrode, in electrical equipment, in batteries, as a catalyst, and in fungicides. Some of these, especially its use in fungicides and as a catalyst, have caused serious human poisoning, as have have seen.
Paracelsus, the author of the first monograph on occupational diseases, published in 1567 after his death, described in detail the effects of chronic mercury poisoning, distinguishing between the acute and the chronic effects. As a physician, he also devised a use for mercury to treat syphilis, which was used for more than 300 years.
Bernadino Ramazzini was the father of occupational medicine. Born in i633 in Italy, he studied the way diseases occurred in groups of people engaged in similar work or living in a particular area. This science we now call epidemiology is an important means of associating a particular disease with exposure to a chemical. Ramazzini studied at first hand the conditions workers had to endure as part of their daily lives.
From early times working people have been exposed to toxic substances ranging from minerals and metals that were mined and then worked into products, for example asbestos, lead, and mercury, to more complex chemicals produced or used in the synthesis of the countless products we now enjoy, such as plastics and drugs. There are numerous chemicals to which workers can now be exposed, some of which may be toxic.
Occasionally, people other than the workers in the factory are exposed, as occurred during the terrible Bhopal disaster in India (see pp. 172-4) and in Seveso (see pp. 123-4). The Seveso incident, mercifully, did not result in any human deaths, causing mostly the skin disorder, chloracne. This severe acne is also a common response to other halogenated (for example, chlorinated) hydrocarbons, which is used in industry or produced as part of the manufacturing processes of pesticides and fire retardants, for example. Despite the obvious potential dangers, industrial chemicals, if used carefully in controlled conditions, often benefit us greatly by producing cheap, durable materials such as plastics, novel fabrics and dyes, and effective drugs. Unfortunately, there have been problems in the past as a result of bad industrial practices such as inadequate safety measures and poor maintenance. Some of the examples that follow will serve to illustrate the lessons that can be learnt.
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