Chapter XXVIII: Dangers in the Use of Mercury and Its Salts

_Introduction._--The number of industries and the number of persons coming into contact with mercury in this country is not large. Probably not more than 500 to 1000 persons are exposed to the danger of industrial mercurial poisoning in Great Britain, but no matter how the metal or its salts are used, those handling it run considerable risk. In some industries, indeed, as, for instance, the silvering of mirrors with an amalgam of tin and mercury, which was for over a century the great source of mercurial poisoning, the matter is now only of historical interest, as the process in question has been replaced within the last twenty years by an innocuous one in which mercury is not used. On the other hand, fresh industries arise in which the metal is used, as, for example, the manufacture of electrical meters and incandescent electric lamps.

_Historical._--As far back as the year 1665, in the _Philosophical Transactions_ of that year, a reference is made by Dr Walter Pope to the tremor affecting the hands of a worker in some cinnabar mines in Italy. In 1721 Antoine de Jussieu[88] described the symptoms of salivation, ulceration of the gums, and tremor which affected the workers in the quicksilver mines of Almaden, in Spain. In the various translations of Bernardino Ramazzini’s work, _De morbis artificum diatriba_, originally published in 1702, an account is given of the effect of mercury on miners and gilders.

One of the first references to the occurrence of mercurialism in the process of silvering of mirrors was made by Bateman[89] in 1812, but the great work which still remains the classical work on the subject of chronic industrial poisoning, due to mercury, was published in 1861 by Adolf Kussmaul,[90] Professor of Medicine in Erlangen. The splendid use which he and other medical men made of the opportunities offered them of studying the clinical symptoms among persons employed in the silvering of mirrors in Fürth and Nuremberg, the principal seats formerly of the industry on the Continent, and the publication of their observations, led up to the introduction of the stringent regulations which have since caused the process to be given up.

In 1829, Dr Reitz[91] of St Petersburg published an account of the danger to health in hatters furriers’ processes in that city, and showed that the solution (regarded then as it still is as a secret), contained mercury, arsenious acid, and nitric acid.

He does not particularly refer to the occurrence of tremor, but describes the death of three men from acute bronchitis after mixing the nitrate of mercury solution.

_Industries in which Poisoning may occur._--The industries in which mercurial poisoning may occur are:--

1. Recovery of the metal from the ore.

2. Separation of gold and silver from their ores by means of an amalgam with mercury.

3. The manufacture of barometers and thermometers and other philosophical instruments.

4. The manufacture of incandescent electric lamps, where mercurial pumps are used to create a vacuum.

5. The manufacture of electrical meters.

6. Gilding and silvering, generally known as water-gilding: where an amalgam of gold or silver is applied to the objects, and the mercury volatilised by heat.

7. Chemical works: where pharmaceutical mercurial preparations are made.

8. Paint and colour works: where anti-fouling paints or vermilion are made.

9. In hatters furriers’ workshops: from the brushing of rabbit skins with an acid solution of nitrate of mercury.

10. Bronzing with a solution of nitrate of mercury: as in bronzing the inside of field-glasses.

In the first six the poisoning takes place almost entirely through the inhalation of mercurial vapour, and hardly at all from dust; in (7) it may arise either from vapour or from, as is the case in (8), contamination of the hands and subsequent ingestion of the salts; in (9) it results from the inhalation of fumes or the ingestion of particles of fur impregnated with nitrate of mercury.

Other processes which deserve mention as a possible source of mercurial poisoning are: electrical engineering, mercury being used in amalgamating zinc plates; taxidermy when corrosive sublimate is used; the manufacture and use of fulminate of mercury in explosive factories; sole-stitching by the “Blake sole-stitching machine,”[92] in which mercury is used to prevent the escape of gas.

_Mode in which Poisoning is brought about._--Mercury in the liquid form, even when swallowed in large amount, rarely gives rise to poisoning. When absorbed in the form of vapour it frequently does, but it would be wrong to suppose that the vapour can as such pass through the lining walls of the alveoli of the lungs. It must first undergo condensation, and the tiny globules so formed become oxidised and then dissolved. In view of the fact that expired air is warmer than that inspired, it is difficult to see where this condensation takes place. Von Renk[93] carried out a series of experiments to see whether the mercury that was scattered in rooms where the silvering of mirrors was carried on could be swallowed with the dust. He found, however, such small quantities of dust in the air (only 7.3 milligrammes in 712 litres of air) that he concluded absorption of mercury in this way was improbable. On the other hand, mercury gives off vapour at ordinary temperatures, the amount depending on the vapour tension, and he found appreciable quantities (2 milligrammes) in a cubic metre of air in a room without special ventilation immediately above a layer of mercury half a square metre in area. As in eight hours a worker inhales and expires about 3 cubic metres of air, if the air breathed were charged only to an extent of 1.5 milligrammes per cubic metre, it would mean that 4.5 milligrammes entered the lungs. Were this continued day after day, injurious effects would necessarily ensue.

The reactions which enable mercury to enter the circulation are only imperfectly understood. It is acted on more readily by salt solution than by dilute acids. The presence of both salt solution and free acid must favour greatly the solution of the metal. Corrosive sublimate forms an albuminate with albumen insoluble in water, but readily soluble in the presence of salt solution. In this remarkable reaction of the solubility of albuminate of mercury in presence of sodium chloride lies the probable explanation of the occurrence of mercurial poisoning.[94]

_Symptoms._--Although in industrial mercurial poisoning the symptoms occasionally resemble those which result from the internal administration of full doses of mercury, such as excessive salivation, swelling and ulceration of the gums with fœtor of the breath, followed in severe cases by looseness and falling out of the teeth, they are as a rule much slower in their onset and more insidious in character. For years the only sign may be more or less gastric disturbance, a gradually increasing anæmia, a slight increase in the secretion of saliva with tendency to ulceration of the gums, and slight tremor of the muscles of the face and hands, accompanied by a certain amount of nervousness.

Kussmaul, from his wide experience among the silverers of mirrors in Fürth, describes three stages in industrial mercurial poisoning: first, erythism or psychical changes; secondly, tremor; and thirdly, the final or cachectic; and my own experience points to the correctness of his description.

The first commences usually in the digestive tract with slight stomatitis and salivation. The worker becomes pale and loses his appetite. He frequently has headache, giddiness, and transitory pains in the limbs. The muscles of the face twitch, the fingers tremble when spread out, and the tongue is also tremulous when protruded. The mental condition undergoes change. Workers assured of their skill become shy and nervous, especially when watched. Sleep is often interfered with and broken by nightmare. Sometimes the tonsils and pharynx become involved in the inflammatory processes affecting the mouth.

At this stage if the employment be given up, the symptoms disappear in about three weeks. If not, the weakness of the muscles increases. Palpitation, headache, sleeplessness, and emaciation all become worse.

In the second stage of tremor, disturbance of the muscular system preponderates. It is observed principally in the muscles of the face, hands, and arms; more rarely in the legs. At first it may amount only to slight tremulousness, but gradually it advances until the movements become convulsive in character, and the hand cannot be directed with certainty to any particular object. The speech, from involvement of the muscles of articulation, becomes slow and indistinct. The psychical condition changes to one of depression or despondency. There may be hallucinations, loss of memory, and dulness of the intellectual faculties. In women, menstruation is diminished or ceases. Miscarriage is frequent, and the offspring is liable to be the subject of rickets or scrofula.

The condition of the teeth of persons exposed to the fumes of nitrate of mercury in hatters furriers’ processes deserves separate mention. The typical appearance in the teeth of those who are engaged in “carotting,” that is, brushing the rabbit skins with the dilute acid solution for several years, is loss of the molar teeth in the upper and lower jaws. The upper incisor and canine teeth are not infrequently absent, and such teeth as remain (generally the lower incisors and canines) are characteristically blackened and often loose. They show a marked tendency to erosion (a process quite distinct from caries, as the enamel and not the dentine suffers most) from the acid fumes, and frequently the gums recede, so that the anterior surfaces of the roots are exposed.

Chronic mercurial poisoning does not frequently lead directly to death. It appears to lower the vitality of the tissues markedly, and Kussmaul calls attention to the frequency with which mercurial workers die of phthisis.

_Recovery from the Ore._--The principal ore from which the metal is obtained is cinnabar, or sulphide of mercury. It occurs principally in Idria in Illyria, where the greater part of the male inhabitants are concerned with its extraction, in Almaden in Spain, and also in China, Peru, California, and in smaller quantity in some of the German States.

The extraction of the metal depends on the principle that by heating the ore in the presence of air, oxidation of the sulphur present results, while the mercury is liberated in the form of vapour, which is condensed in suitable flues kept constantly cool by a stream of water. Complete condensation of the vapour is difficult.

In the actual mining of the ore, poisoning does not occur. Danger principally attaches to the smelting operation, to the cleaning out of the flues, and to the packing of the quicksilver.

The amount of illness caused may be judged from the fact that between the years 1879–1884, of 1000 workers, 112 suffered from mercurialism, although this figure does not take account of gastric symptoms, which, if included, would raise it to 200 or 250 per 1000.[95]

The dangers can be best avoided by suitable arrangement of the furnaces so as to prevent the escape of fumes, the wearing of overalls, and ample provision of washing and bath accommodation.

_Making of Thermometers._--In the making of thermometers a small funnel is blown on the top of a capillary glass tube and filled with mercury. Heat from a spirit lamp or gas jet is applied to the bulb, and the expanded air partially escapes. On cooling, a portion of the mercury passes into the bulb to take the place of the air which has escaped. This process is repeated until the bulb and part of the tube are full of mercury. The mercury is then heated to boiling, mercury vapour escapes, carrying with it the air and moisture which remain in the tube. The tube, when full of the expanded mercury and mercury vapour, is hermetically sealed at one end.

The number of persons employed in the industry of thermometer and barometer making is small. They generally describe themselves as experimental glass-blowers. The processes are usually carried on in small workrooms, the conditions in which, owing to the wooden benches and floors affording lodgment in the crevices for particles of mercury and to the gas jets alight at every bench, are not conducive to health. Close observation of almost every worker who has been employed for a few years (and when once entered on it is rarely exchanged for another), reveals the presence of chronic mercurialism either in slight tremor of the muscles of the face or hands, or the characteristic earthy complexion.[96]

_Incandescent Electric Lamps._--In the manufacture of incandescent electric lamps, if mercurial pumps are used to produce the vacuum in the glass envelope, the danger from the scattering of mercury, which not unfrequently happens through breakage and careless manipulation, is considerable.

In Berlin and Buda Pesth[97] several cases of chronic poisoning from this source occurred a few years ago. The industry, so far as the operations in the pump-room was concerned, was placed under special regulations in Berlin, requiring (1) mechanical ventilation; (2) overalls and head coverings for the persons employed; (3) provision of a meal room and the washing of hands and face with soap, and the rinsing out of the mouth with potassium chlorate before meals; (4) a warm douche bath three times a week; (5) medical examination of the workers once a week. The effect of these regulations was a cessation almost at once of mercurial poisoning, and they soon led to the introduction of mechanical pumps to replace those of mercury.

In this country no case has been reported in this industry, and the evidence I have found so far of mercurialism among the workers is slight.

_Electrical Meters._--The same dangers from the free use and handling of mercury is to be found in workshops where electrical meters are made, and they can only be satisfactorily met by the adoption of the precautions mentioned in the last section of this chapter.

_Gold and Silver Extraction._--Both gold and silver are occasionally separated from the ores in which they are found by amalgamation with mercury, the latter subsequently being removed by distillation.

_Water-gilding._--In the gilding and silvering of ornaments, the use of mercury has fortunately been almost entirely replaced by the much less harmful electroplating. The gilding, however, produced by the amalgam with mercury and subsequent firing (water-gilding) is more durable than that obtained by electroplating, but such articles as military buttons are still prepared in the old dangerous way, although greater precautions are taken to see that the fumes are carried away. The object to be gilt is treated with a solution of nitrate of mercury, and the amalgam (previously prepared by heating an alloy of gold with silver and copper to redness, adding an eighth part by weight of mercury, subsequently cooling in water and expressing any excess of mercury) is applied with a brush. Formerly the article was heated over a charcoal fire, with, necessarily, escape of fumes both of carbonic oxide and mercury into the room. Now it is done either in a closed stove or on a gas jet with a good draught.

_Silvering of Mirrors._--The process of silvering of mirrors, which formerly caused so much suffering, was to spread out on a perfectly horizontal table of marble or glass a sheet of tinfoil. On to this a small quantity of mercury was poured to form an amalgam. A large quantity of the metal was then added, and the carefully polished plate of glass was slid over it, pushing some of the excess of mercury in front, which was collected in small channels, but abundance remained in the cracks and crevices of the tables. Heavy weights were placed on the glass to press out the mercury, and in a few days the combination of mercury and tin was found to have adhered firmly to the glass.

It may be well to refer here to the process which has taken its place. The method is a wet one, and consists in pouring over the cleaned and dried glass plate a solution of nitrate of silver, containing an alkaline reducing agent, such as a tartrate, or more commonly ammonia. A reddish or black precipitate at first falls down, and later on a shining surface of metallic silver holds close to the glass. The glass is then carefully wiped dry and backed with a coat of varnish or red lead. Cases of lead poisoning have occurred from the use of red lead in this way.

Statistics of Dr Wollner[98] show that in 1885, on an average, 160 persons were engaged in the silvering of mirrors in Fürth. Among these there were 165 illnesses (103 per cent.) for which sickness insurance money was paid, and of these 60.6 per cent. were on account of mercurial poisoning. The percentage among males and females was practically the same, but the number of sick days was greater in the case of men than in that of the women--66.7 days as compared with 50.5.

In 21 per cent. symptoms became prominent in from one to two years, in 61 per cent. in two to six years, in 15 per cent. in six to ten years, and in 3 per cent. in ten to seventeen years.

In 1898 the Factory Inspector for the district of Fürth states in his report that only seven persons were engaged in the process, and that their employment was intermittent. As the process has thus become practically extinct, it is hardly necessary to give the regulations enforced in Germany since 1889, but they are well worth reading by those who are anxious to bring to an end particularly dangerous industries, especially when they are carried on in the homes of the workers.

_Hatters Furriers’ Processes._--Mercury in the form of a dilute solution of the nitrate is used in the preliminary process of felt hat making to increase the felting properties of the rabbit fur. The industry employs in the mercurial process alone between two and three hundred men and women. After the longer hairs have been removed by fur pullers, the rabbit skins are subjected to a process known as “carotting,” in which they are brushed with the above solution. When dried they are brushed by machinery to loosen the fur, and then each rabbit skin is passed through an ingenious machine with rotating knives so arranged as to cause the skin to be shaved off in strips, leaving the fur intact.[99]

Few combinations can be imagined more likely to affect detrimentally the health and more particularly the teeth of workers than that of mercury and nitric acid. As might be expected, those engaged in “carotting” show in most marked degree injury to the teeth from the nitric acid fumes, the typical condition of which has already been described, while tremor and erythism predominate in those engaged in the later processes as the result of the inhalation of particles of fur impregnated with the nitrate of mercury.

The following figures make this clear, giving the result of an examination made by me of 111 persons in eight different factories, who had worked for one year and upwards--

+---------------+---------+-----+-----+-----+-----+-------+-----+
| Process. | Number |Teeth|Per |Teeth|Per |Tremor.|Per |
| |examined.|Bad. |cent.|Fair.|cent.| |cent.|
+---------------+---------+-----+-----+-----+-----+-------+-----+
|Carotting | 30 | 20 | 66.6| 10 | 33.3| 1 | 3.3|
|Other processes| 81 | 27 | 33.3| 54 | 66.6| 17 | 21.0|
+---------------+---------+-----+-----+-----+-----+-------+-----+

A “fur” as received from the cutting machine, analysed in the Government Laboratory, was found to contain 1.34 per cent. of nitrate of mercury. The mercury forms a very insoluble combination with the keratine in the hair which is not removed in the subsequent processes of felt hat making. Jungfleish[100] found in a layer of felt which had been deposited on the revolving cone used in making hats nearly 0.5 per cent of metallic mercury, and in a felt hat which had been worn for a long time 0.7 per cent. Nevertheless, mercurial poisoning even of slight degree does not occur, or at any rate only very exceptionally, in the later processes of felt hat making.[101]

_Preparation of Mercurial Compounds._--In factories where mercurial compounds are made, such as calomel, corrosive sublimate, the red oxide (largely used as an anti-fouling paint for ships’ bottoms), and vermilion, there is considerable evidence of mercurial poisoning among the workers. For instance, of 27 men so employed, I found in four (15 per cent.) more or less salivation, and in ten (37 per cent.) tremor, besides such other symptoms as anæmia and gastric derangement. Danger arises from the volatilisation of the metal in the subliming operations, and also to some extent from the dust which, though very heavy, can become scattered, if such processes as mixing, sifting, and grinding are not carried out with care in closed-in vessels.

Calomel, subchloride of mercury (HgCl), is made either by intimately mixing corrosive sublimate with metallic mercury and subsequent sublimation, or by mixing definite proportions of mercuric sulphate, metallic mercury, and common salt. The mixture is then heated so that the calomel may pass off as vapour and be condensed in the cool subliming chamber. Finally, it is ground wet, dried, and sifted. All these later stages in the preparation must be carried on in a closed apparatus, and with observance of great care.

Corrosive sublimate, the bichloride of mercury (HgCl_{2}), is made by heating two parts by weight of mercury with three parts of strong sulphuric acid. To the mercuric sulphate so formed when dry, one and a half parts of common salt are added. The corrosive sublimate is converted into vapour by heat, and condenses on the upper cooler portion of the vessel in lustrous colourless masses, leaving a cake of sulphate of soda below. The sublimate is then scraped out, and usually undergoes no further treatment such as grinding. The operation of sublimation requires very constant attention on the part of the worker to prevent the vessels in which the vapour sublimes being overheated, and so allowing its escape.

In the preparation of red oxide of mercury, nitrate of mercury is first made, in which care has to be taken that the fumes so developed are carried away by ventilating shafts in connection with each vessel. The crystals formed after evaporation are ground with addition of metallic mercury, and then heated in an oven. Nitrous fumes are evolved, and the oxide, black when hot, turns to a brilliant red crystalline powder on cooling. Finally, it is ground wet, dried, and sifted.

Vermilion, sulphide of mercury (HgS), is made by mixing excess of sulphur with metallic mercury in closed rotating wooden drums. Black amorphous sulphide of mercury results,[102] which on heating to 150° C. becomes converted into a dark violet powder. From this vermilion is obtained by sublimation, a process attended with risk from escape of vapour. Finally, it is ground wet, and according to the fineness of the grinding so is the particular shade of colour obtained.

The manufacture of calomel, corrosive sublimate, and vermilion can be made by a wet method throughout without danger, provided reasonable care is taken.

_Preventive Measures._--The conditions to be aimed at in places where metallic mercury is handled (and for the most part also in places where salts of mercury are used), are as follows:--

1. The flooring and benches should be smooth, impermeable, and free from cracks or crevices in which mercury can lodge. Preferably the floor should be of some kind of asphalt or cement, laid in such a way that channels all converge towards a receptacle where the scattered mercury may collect. Wood, although at present in common use, is not well adapted for the purpose. The receptacles should be covered over, leaving only a narrow opening for the mercury to run in.

2. There should be ample light, and the windows of all rooms where mercury vapour may be produced should preferably face the north.

3. Mercurial processes should be carried on in rooms separate and distinct from the other workrooms.

4. Any unnecessary raising of the temperature above 60° F. is to be avoided, and consequently there should be no direct heating of the rooms by open fires or stoves.

5. Mechanical ventilation should be provided, and reliance not be placed merely on differences of temperature between the outside and inside air. Inlets for air should be above the level of the heads of the workers, and the draught of the fan should be a downward suction one.

6. Workers should wear overalls and head coverings.

7. Shortness of the hair, shortness and cleanliness of the nails, a proper hygiene of the mouth, and baths, would do much to protect the workers. Ample washing convenience, including soap, nail brushes, and towels, should be provided.

8. Meals should be prohibited in any room where mercury is handled.

9. Periodical medical examination, with power to the surgeon appointed to suspend temporarily or permanently from work.

* * * * *

In two of the largest factories in which mercurial preparations are made, in addition to the carrying out of all dusty processes such as mixing and sieving, as far as possible, in a closed-in apparatus, the following measures have been taken:--

RULES TO BE OBSERVED IN THE MANUFACTURE OF MERCURIAL
PREPARATIONS.

1. The firm will appoint a surgeon to examine all persons
employed in mercurial processes at least once in every month,
and he will undertake any necessary medical treatment of illness
contracted in consequence of such employment. He will have power
to suspend any such person from work in any place or process.

The surgeon will enter in a register the dates and results of
the examination of the person employed as above. No person after
suspension can be employed in any mercurial process without
written sanction from the surgeon.

Every person employed in a mercurial process must present
himself at the appointed time for examination by the surgeon.

2. The firm will provide sufficient and suitable overall suits
for the use of persons engaged in the processes of sifting and
grinding, and every person when so engaged must wear an overall
suit.

3. The firm will provide respirators approved by the surgeon for
persons engaged in processes where there is unavoidable dust,
and every person so employed must wear the respirator.

4. The firm will provide and maintain washing conveniences
in the proportion of one lavatory basin to each five persons
employed, with soap, nail brushes, and towels, and a constant
supply of hot and cold water laid on to each basin.

Every person must, before meals and before leaving the premises,
thoroughly wash in the basins provided, and those who have worn
overalls and respirators must deposit them before leaving the
factory after the day’s work in the place appointed for the
purpose by the firm.

The firm will see that the overalls are washed once a week, and
the respirators renewed or washed every day.

5. The firm will provide and maintain a bath with hot and cold
water laid on, and a sufficient supply of soap and towels. Every
person shall have the opportunity of taking a bath at the
factory once a week, and those whom the surgeon directs must do
so.

Each person taking a bath must sign his name in a register.

6. The firm will provide and maintain a cloak-room in which
workers can deposit clothing put off during working hours,
separate from any portion of the works where mercurial processes
are carried on.

7. No food or tobacco are to be taken into, nor is food to be
eaten in any part of the factory where mercurial processes are
carried on.

8. The foreman must report to the manager any instance coming
under his notice of a workman neglecting to observe these rules.

_Note._--The danger against which the rules are directed is
that of mercurial poisoning, of which the principal symptoms are
soreness of the gums, offensive breath, increase in the amount
of spittle, and trembling of the fingers. Workers are warned of
the danger arising from the chewing of tobacco, and of eating
food with unwashed hands. Mercury has a tendency to destroy the
teeth, and this can be best obviated by the use of a tooth-brush
once every day.

In hatters furriers’ processes the remedial measures required are rather different, although suggestions (6), (8), (9), and part of (7) equally apply. It is necessary in this industry to remove the fumes arising from the solution of nitrate of mercury in carotting, and to secure the absence of dust at the cutting machines, either by perfecting the machinery and fittings of the receptacles into which the bulk of the dust is carried by the revolving knives, or by increasing this draught by means of a fan. This latter mode has been adopted with success both as regards removal of dust and economy of work. It is desirable, too, that the primitive stoves at present in use for drying the “carotted” skins should be replaced by the kind now commonly to be found in steam laundries, of “horses” sliding in and out of the heated chamber on rails.

By the French law of 13th May 1893, the treatment of the skins and fur of hare and rabbit skins with nitrate of mercury is scheduled, with others, as an industry in which neither children nor females may be employed.

T. M. LEGGE.