First among the major studies of mercury poisoning in the American felt-hat industry was that made by Dr. J. A. Freeman of New Jersey and reported in 1860. Freeman’s findings were confirmed in a report published by the Board of Health of the State of New Jersey in 1878 (Dennis). In 1910, under the aegis of the Women’s Welfare Department of the New York and New Jersey section of the National Civic Federation, Mrs. Lindon W. Bates, assisted by Miss Florence Roehm, undertook a survey of industrial mercury poisoning in the New York metropolitan area. The results were published in 1912 (Bates). Dozens of cases of severe mercurialism were found among hatters, a state of affairs which was confirmed by the New York City Department of Health in 1915 (Harris).  

Additional reports on the health of hatters appeared during the 1920’s, notably those of Alice Hamilton (1922a, 1922b), Wade Wright (1922) and the United States Public Health Service (Neal et al. 1937, 1941). The last are of particular significance.  

Just as it is unfair for modern scientists to scoff at Pliny or at the alchemists because much of what was written many years ago now seems to be nonsense, so is it inappropriate to apply present-day standards to some of the studies made as recently as 30 or 40 years ago. This is especially true when analytical chemistry is involved. So dramatic have been the refinements in micro-chemical techniques, that work which is much more than 10 years old may have to be viewed as belonging to an earlier age.  

These brief remarks have been made as a preface to a discussion of the two later major studies of mercurialism in the felt-hat industry conducted by the U.S. Public Health Service during the 1930’s. Because of their scope, these two studies have been widely quoted and, unfortunately, often misquoted. Some of the findings are difficult to understand and, in the light of more recent knowledge, difficult to accept (Goldwater 1964).  

One anomalous finding in the Public Health Service study in the hatters’ fur-cutting industry is the relative infrequency with which mercury was found in the urine of exposed workers. The levels of exposure, 0.06 – 0.72 mg per cubic meter of air, were such that all would have been expected to have mercury in the urine. Yet, according to the tables in the text, only 35 percent of urine specimens from 488 workers had detectable quantities of mercury. Lack of sensitivity of the analytical method employed is the most reasonable explanation for the anomalous results. (The summary of the report states that 65 percent of the specimens contained mercury.) More difficult to explain or understand is that of 33 active workers diagnosed as having mercurialism, 19 showed no mercury in the urine.  

The second of the Public Health Service studies in the felt-hat industry also resulted in some puzzling findings similar to those in the first (Goldwater 1964). This is particularly unfortunate since the American Conference of Governmental Industrial Hygienists, which promulgates standards for permissible levels of exposure to potentially harmful agents in the work environment, chose to use this study as the basis for establishing limits for exposure to mercury (American Conference of Governmental Industrial Hygienists 1962). Fortunately, more reliable data are proposed for use in a revised standard promulgated in 1969 (American Conference of Governmental Industrial Hygienists 1971).  

Still another large-scale investigation of the health of workers in the fur-felt industry was undertaken by the Division of Industrial Hygiene of the New York State Department of Labor in 1936. The findings of this study are rarely quoted, probably because they were not published until 1948 – 1950 (Smith and Moscowitz 1948; Smith et al. 1949; Goldwater 1950; Moscowitz 1950), long after mercury had been eliminated from the making of hats in the United States.  

Most extensive the of the reported studies of mercurialism in the felt-hat industry is that conducted by the staff of the Clinica del Lavoro “L. Devoto” of Milan, under the direction of Vigliani (1953). This investigation covered about 1200 workers of whom 246 were diagnosed as having mercury poisoning. The monograph in which the findings are published is an outstanding contribution to the literature of occupational medicine.  

In her classic work, Industrial Poisons in the United States, published in 1925, Alice Hamilton reviews the general subject of mercurialism in one chapter and devotes a separate chapter to the hat industry. The latter is longer than the former, reflecting the importance attached to health hazards among hatters during the first decades of the 20th century. According to Hamilton, the process of treating the fur with mercury nitrate, the so-called secretage, “…has been traced back to the middle of the 17th century when it was a secret in the hands of a few French workmen, evidently Huguenots; for at the revocation of the Edict of Nantes in 1685 when the Huguenots fled to England, they carried the secret with them, established the trade there, and for almost a century thereafter the French were dependent on England for their felt.” This statement is difficult to reconcile with that which appears in Diderot’s encyclopaedia published in 1753, to the effect that in preparing fur for making hats “…the pelts are rubbed with an acid solution before the fur is removed….” It is also at variance with an account of secretage given by Lee (1968) in which he states that the process was introduced into England from Frankfurt around 1870. The latter is in consonance with Thackrah’s failure to include mercury poisoning in his description of hazards in the British hat industry in the early part of the 19th century.  

The complete story of the process of secretage has been difficult to ascertain, particularly for the period between the middle of the 18th and the middle of the 19th centuries. Some features are well documented while others are not. That the Huguenot hatters left France around 1685 is well established (Unwin 1904; Kellogg 1925; Cunningham 1897; Smiles 1868; Weiss 1854; Erman and Reclam 1782-94).  

Aware of the loss to the French economy of the skills taken out of the country by Huguenot refugees, Louis XIV sent the Marquis de Bonrepaus to England to try to persuade the expatriates to return. The Marquis wrote from London in 1686 that “The other manufactures which have become established in this country, are those of hats of Caudebec, and the dressing, in the best manner of Chamois skins” (Weiss 1854). In commenting on this, Weiss says:  

The manufacture of hats, indeed, was one of the finest branches of business with which the refugees endowed the English. In France, it had been almost entirely in the hands of ‘the Reformed.’ They, alone, possessed the secret of the composition water, which serves for the preparation of the rabbit, hare, and beaver skins, and they alone furnished to trade the fine hats of Caudebec, so much sought after in England and Holland. After the revocation, most of them retired to London, taking with them the secret of their art, which was lost to France for more than 40 years. It was not until the middle of the 18th century, that a French hatter named Mathieu, after having worked long in London, stole the secret, which had been imported by the refugees, took it to his own country, generously communicated it to the hatters of Paris, and founded a large manufactory in the Suburb of Saint Antoine. Before that fortunate theft, the French nobility and all those who prided themselves on the elegance of their dress, wore none but hats of English manufacture, and the cardinals of Rome, themselves, sent for their hats from the celebrated manufactory of Wandworth, which had been established by the refugees.

A clue to the history of carroting in Britain is found in Taylor’s book On Poisons, published in 1975. He describes the case of a man who was admitted to Guy’s Hospital on December 10, 1863, suffering from chronic poisoning by the nitrate of mercury. “He had been for four years engaged in packing the fur of rabbits, rats, and other animals, the dried skins of which had been brushed over with solution of nitrate of mercury.” This clearly is the carroting process (secretage). If the dates are accurate it shows that carroting was being practiced in Britain in 1859.  
  
   

“The Mad Hatter”  

There is some question as to whether or not the Hatter in Alice in Wonderland (1865) was mad because of mercury poisoning. For one thing, the diagnosis may be questioned since it was made rather casually by the Cheshire Cat.  

“In that direction,” the Cat said, waving its right paw around, “lives a Hatter; and in that direction,” waving the other paw, “lives a March Hare. Visit either you like; they’re both mad.” Although the ensuing episode was a Mad Tea Party, and both the March Hare and the Hatter were present, there is no further mention of the latter’s madness. True, the Hatter’s behavior was a bit erratic, but no more so than that of many other characters in the book. His remark to Alice that “Your hair wants cutting” does not necessarily imply that he was thinking of using the hair to make felt (Dodgson 1946).  

Gardner (Dodgson 1960) has pointed out that the phrases “mad as a hatter” and “mad as a March hare’ were in common use in Carroll’s time and that “mad as a hatter” may have been a play on the cockney corruption “mad as an adder.” He suggests, however, that it “…more likely owes its origin to the fact that until recently hatters actually did go mad…” Writing in 1960, Gardner may be referring to the 20th century, since Thackrah failed to note the characteristic erethism of mercury poisoning in hatters in the 1830’s, and the mercurial secretage may not have been reintroduced into England until the late 1850’s (Taylor 1875). Between then and 1865 the symptoms of mercury poisoning in hatters could have been known but could hardly have become a by-word.  

Another interesting point made by Gardner has to do with the appearance of the Hatter in Tenniel’s drawings in Carroll’s book. He rejects what he says was a common belief at the time that the Hatter was a burlesque of Prime Minister Gladstone. Rather, he says, “There is good reason to believe that Tenniel adopted a suggestion of Carroll’s that he draw the Hatter to resemble one Theophilus Carter, a furniture dealer near Oxford…” who was known in the area as the Mad Hatter. He was so designed because he always wore a top hat and partly because of his eccentric ideas and behavior. He invented an alarm clock bed which awakened the sleeper by tossing him to the floor and which was exhibited at the Crystal Palace in 1851. This may have had something to do with the Hatter’s preoccupation with time and with his concern over the dormouse’s somnolence.  

Confirmation of the theory that Lewis Carroll’s “Mad Hatter” was not a victim of mercury poisoning is found in views expressed by a Director of Associated British Hat Manufacturers Limited (who wishes to remain anonymous). Among the credentials which enable this gentleman to speak with authority are the fact that his father’s family have been making hats continuously since 1773 and his mother’s since about 1660. His discussion of the subject of felting clearly shows that he has done considerable research into the historical aspects.  

He points out, in consonance with Gardner’s statement that the expression “mad as a hatter” was in common use in England during the middle of the 19th century, that the expression appears in Chapter 10 of Thackerah’s Pendennis, which was published in 1850. Thackrah’s failure to note the use of mercury nitrate in the hat industry supports the fact that it was not being used in 1830. It was not until the middle of the 1840’s that the felt-hat industry as it is known today, with its use of mercury nitrate, was founded.  

Our anonymous informant (personal communication 1970) has provided an interesting account of the origin of the use of mercury compound in the making of felt.  
  

The felting process began with camel hair in what is now a part of Turkey. The hair of camels was made into tough felt material for tents. It was discovered that the felting process was accelerated with the urine of the camel. The art was brought back to Western Europe by the followers of the Crusades. It become the habit for the workers to urinate on the fibres before felting them. The story goes that one particular workman (probably in France!) was being treated with mercury for a venereal disease. It was noticed that his fibres, after the treatment mentioned above, felted quicker and better than that of his more healthy comrades. This was the secret which gave the process the name of ‘le secretage’ in France. This may be an old wives tale, but it has been passed down in the Felt-hat Industry as the origin of the use of mercury.

Legislation directed toward the prevention and control of occupational mercurialism has followed the pattern of labor legislation in general, although there have been special provisions made for mercury from time to time. Early laws aimed at improving the lot (and the health) of factory workers generally had to do with limiting the hours of work and the employment of women and children. Applied to occupations in which mercury was handled these limiting provisions would certainly be beneficial. Later laws prescribing minimum standards of factory hygiene and sanitation likewise reduced the possibility of occupational poisoning. Minimum wage laws, leading to improved living standards, represent another type of labor legislation that might be expected to benefit employed persons in general, including those occupationally exposed to mercury. Workmen’s compensation laws have had a more direct impact.  

In discussing legislation related to mercury, Biondi states that “The first statutory intervention known dates from 1665, when the hours of work in the quicksilver mines of Friuli (Idria) were reduced to six per day in consequence of the effects on health” (International Labour Office 1930-34). He also records the existence of special legislation restricting women and young children from working with mercury in the Netherlands, Japan, France, Switzerland, and Greece. Hamilton (1925) says much the same thing. In countries having workmen’s compensation laws, mercury poisoning is recognized a compensable occupational disease subject to the general provisions of the laws. Great Britain enacted special Mercury Process Regulations in 1963, the culmination of a series of regulations which began when mercurial poisoning was made a notifiable disease in 1899, under the provisions of the Factories Act (Lee 1968). In France, a decree issued in 1913 and modified in 1935, was designed to protect the health of workers in the fur cutting industry in plants where the fur had been treated with mercury nitrate (Desoille 1949).