Lead poisoning and lead absorption

Lead smelting—Red and orange lead and litharge—Letterpress printing—File-cutting—File-hardening—Tinning of metals—Plumbing and soldering—Brass.

Lead Smelting and Silver Refining.

—Lead poisoning very rarely occurs in lead mining in Europe, as galena (sulphide of lead), the principal ore in which the metal is found, is insoluble. Galena always, and other lead ores very often, contain a small proportion of silver, ranging from 0·001 to 1 per cent., and at times traces of gold. Owing to the great affinity of lead for silver, lead smelting is necessarily a process preliminary to the extraction of silver and gold from it[1].

Lead ores, drosses, etc., on arrival at the factory, are, after sampling, deposited in bins or heaps (often in the open air), and watered to prevent dust. All ores may, and refractory ores (containing over 4 per cent. silica) and dross must, be smelted in a blast furnace by aid of coke. The bulk of the charge in a blast furnace may consist of more or less complex ores of the precious metals, especially silver.

When galena is treated in a blast furnace, preliminary roasting is indispensable, and in many smelting works its treatment takes place in a reverberatory or open-hearth furnace, and not in a blast furnace.

The three principal methods applicable to extraction of lead from ores are—(1) The roast and reaction method; (2) the roast and reduction method; and (3) the precipitation process.

By the roast and reaction method a part of the galena is first converted into oxide and sulphate of lead with access of air. Subsequently, on shutting off the air-supply and increasing the temperature, a reaction takes place. The sulphur in the unchanged sulphide combines with the oxygen of the oxide and sulphate to form sulphur dioxide, which is carried away by the draught into the bricked flue, leaving metallic lead behind. The process is carried on in a reverberatory or open-hearth furnace.

In the roast and reduction method the first portion of the process is carried out in a reverberatory furnace, the galena being roasted pretty completely to lead oxide and sulphate, which are then—usually in a blast furnace—reduced to the metallic state with coke and other reducing agents, such as iron.

By the precipitation process galena was decomposed at a high temperature by means of metallic iron, forming a mixture of iron and lead sulphide. This method was only applicable to rich lead ores, and is now given up.

The three methods are hardly ever independent of one another, as the rich slag or residues, for instance, which are obtained by the first method are retreated by the second, and the second is, as has been stated, almost always combined with the first.

On tapping the blast or reverberatory furnace, the lead is drawn off into a lead well or sump, from which, when cool, it is ladled into moulds, while the slag is run into movable metal pots or along specially-prepared channels. The slag run off from the reverberatory furnace contains much lead locked up as silicate, which requires to be retreated, usually in the blast furnace. During the roasting process much raking of the material is necessary. The slag from the blast furnace should contain less than 1 per cent. of lead.

On the Continent and in America, the Huntingdon-Heberlein process has been extensively adopted, with lessened incidence of poisoning, the result of mechanical methods of working, obviating hand labour, and the low temperature (diminishing risk from lead fume) at which the roasting is carried on. In this process the crushed ore is desulphurized by first mixing with lime and heating in presence of air in a revolving furnace, provided with automatic rabble, at moderate temperature (about 700° C.). Subsequently the roasted material is conveyed from closed bins, into which it falls automatically, by dust-proof elevators to a converter, in which atmospheric air at slight pressure is forced through it. The agglomerated mass so formed, when tipped out of the converter (in doing which there is risk from dust), is well damped, broken by hand, and charged with coke in the usual way into the blast furnace.

In some lead-smelting works the material arrives on the premises in the form of ingots of base bullion—i.e., impure lead rich in silver—the product of previous smelting of the ore where it is mined in Australia or Spain. And one of the main objects of the blast-furnace smelting of galena in the factory is to produce a base bullion rich in precious metals. The lead so obtained requires further softening or refining to get rid of copper, antimony, arsenic, and tin. This is effected in a reverberatory furnace, first at a low temperature to allow of formation of furnace dross, which is removed through the working doors, and secondly with increase of heat and access of air to oxidize, in the order named, the tin, arsenic, and antimony. Finally the lead is tapped into kettles or pots. If free from silver, such lead, when poured into moulds, is ready for the market; but if rich in silver, it is treated for the recovery of that metal either by (a) Pattinson’s process, depending on the higher temperature of crystallization of lead than of an alloy of lead and silver, which enables a separation of one from the other to be made by a process of ladling the crystalline from the liquid portion; or, much more commonly, by (b) Parkes’s process, depending on the formation, on addition of zinc to a pot of molten lead, of crusts consisting of an alloy of silver, lead, and zinc. The crusts obtained in the latter process, after cooling, are broken up, placed in a crucible, and the zinc driven off at a temperature of 1,000° C. in a dezincing Faber du Faur retort. The rich bullion, retained either in the last kettle by the Pattinson process, or remaining in the crucible after dezincing, next undergoes cupellation—i.e., exposure to a blast of air in a furnace. The lead is oxidized into litharge, which drops into a receptacle below the furnace, leaving the silver behind. In all lead-smelting works the draught from the furnace carries much dust of ore and fuel, and fume, consisting of sulphide, sulphate, and oxides of lead, into the flues. The dust is easily collected in dust chambers, but the fume requires ducts of great length—sometimes a mile or more—in which to deposit.

Dangers and Prevention.

—The risk from dust in general labouring work, in depositing the ores in bins, in removing them to, and charging them into, the furnace, can only be controlled by watering, preferably by a spray. From the blast furnace lead fume and carbon monoxide may escape at the point where charging is done, if there is back pressure from blockage in the flues, or if the furnace blast is not working perfectly. In tapping the lead and in manipulations such as charging, drossing, and skimming, conducted through the doors of furnaces of all descriptions, hoods, extending at the sides down to the floor level, require to be arranged over the working doors, and connected either with ducts passing vertically through the roof or directly with the exhaust created in the furnace or flue itself. Dross and skimmings removed through the working doors should be received into iron trolleys capable of being covered, and not be allowed to fall on to the floors, to be shovelled up later on to barrows. Before such dross or slag from reverberatory furnaces is broken up for further treatment it should be well watered.

Lead absorption among the men actually employed in the Pattinson and Parkes’s processes is comparatively rare, as the temperature of the molten metal does not exceed 450° to 500° C. When, however, the zinc-silver-lead and gold alloy is removed for treatment in special furnaces for distillation off of the zinc, prior to cupellation, the lead from the Parkes’s pot, now free from silver, but containing traces of zinc, antimony, and other impurities, is run in some works into what are termed “market pots” for a final refining. Air and steam are blown through to oxidize the impurities. The pot is skimmed twice, the first dross containing antimony, etc., and the second a fine dust consisting of lead (60 per cent.) and zinc. The risk of poisoning at this point is considerable, although an exhaust fan connects up the cover of the pot with a cyclone separator, to carry away the fume when the steam is blown through. In other works this dezincing is done in a refining furnace, the material being then in a slaggy state, thus hindering development of fumes. After the condensation of the zinc in the distillation of the silver-lead and zinc crust the cover of the pot is raised, and the remaining metal, containing 80 per cent. of lead at a temperature of about 2,000° F., is ladled out into moulds for treatment in the cupelling furnace. The temperature at which this ladling operation has to be done makes the work impossible for those unaccustomed to it. Exhaust ventilation in the operation of emptying the pot, and cutting off the heat by a water-cooled jacket, suggest themselves as means to combat the undoubted risk.

In cupellation the temperature is high (about 2,000° C.), and fume will escape from the working door and from the opening where the rich lead is fed into the furnace. The danger here is sufficiently recognized by hoods and ducts placed in front of the furnace, but the draught, unless the ducts are connected up with a high-pressure fan, may prove inadequate to carry away all the fume.

Flue-cleaning, carried out usually at quarterly or half-yearly periods, is dusty work, as much of the dust is in so fine a state of division as to repel contact with water.

Smelting of other metals when the ores contain appreciable amounts of lead is equally productive of plumbism. Thus, in the year 1901 fourteen cases were reported from an iron works for the manufacture of spiegeleisen, the ore (now no longer used) coming from Greece[2]. In previous years it would appear to have been even greater. A remarkable feature of all the reported cases from this factory was that the form assumed was colic, and never paralysis. The poisoning was due to vaporization of the molten lead by the very high temperature to which it was raised as the molten iron flowed out of the furnace on tapping. The danger from fume was limited to the first few feet of the channel, as the heavier molten lead gravitated down between loose brickwork into a pit. Dust collected above the point where the furnace was tapped contained 39·77 per cent. of lead monoxide, and the flue dust 4·22 per cent.[3]. A flannel respirator worn once only by one of the furnace men contained lead equal to 16 milligrammes of lead monoxide. In 1906 three cases were reported in the extraction of copper. The persons affected were employed in charging ore into the cupola[4].

Heavy incidence of poisoning (twelve cases in two months) in a smelting works (now closed) led to examination of sixteen men. The gums of only one man were free of a blue line—in most it was particularly dense—eight were anæmic, one had paralysis of the wrists, and five others weakness. Analysis of the air was made at different points in the factory by the chemist of the works, G. D. Cowan, with the following results:

Assuming that 20 cubic inches of air pass in and out of the lungs at each respiration, a man in eight hours would inhale and exhale 94·4 cubic feet. This amount of air, inhaled at the position in the cupola where the sample was taken, would contain 7·3818 grains of lead; at the lead well, 5·3064 grains; and at the briquetting machines, 91·5953 grains. Although the condition of the air where the men actually worked must have contained much less than these amounts, the analyses quite serve to explain the heavy incidence.

Collis[5] quotes the following analysis of dust and fumes from Hofman’s “Metallurgy of Lead.”

Lead Smelting: Analyses of Dust and Fumes (from Hofman’s “Metallurgy of Lead”).

Collis[6] estimated the attack rate in lead-smelting works at 30, and in spelter works at 10, per 1,000 per annum. In one factory he found it 80 per 1,000, and in a spelter works five cases occurred in a few months among seven workers.

The distribution of the reported cases from year to year was as follows:

Spelter (Zinc) Manufacture.

—Lead is present in zinc ores in a proportion of from 1 to 10 per cent. (usually 3 per cent.). Despite this small proportion, incidence of chronic plumbism among those engaged in the manufacture is high, as in the present state of knowledge the lead fume given off in distillation of the zinc cannot be efficiently removed. Blende (zinc sulphide) is first calcined, and the residue, after mixture with calamine (zinc ashes) and anthracite, forms the charge for the furnace. The retorts are arranged in long rows one above the other, and frequently back to back in the furnace, so that there may be 250 or more to each furnace, and of the furnaces there may be several in a shed. Attached to the retort is a fireclay receptacle (condenser) into which the zinc distils, and an iron nozzle (prolong) to prevent oxidation in the condenser. While distillation goes on the carbonic oxide gas evolved burns brightly, tinged with the greenish-white colour imparted by the zinc. The products of combustion, with traces of lead fume from the hundreds of prolongs, are discharged into the atmosphere of the sheds, where temperature is high. The latest design of prolongs, however, has an exit at which the products of combustion escape near the furnace, so that the greater portion pass up into the ventilating hoods. Periodically—three times to each charge—the workman removes the prolong, ladles out such zinc as has condensed, and pours it into moulds. Finally, when distillation is completed, the contents of the retorts are raked out, and it is in the fuming hot residues so deposited on the floors that much of the danger arises. In distilling furnaces of modern design the hot residues fall through openings in the window of the furnaces into “pockets,” in which they cool off considerably before they are drawn out into iron skips. In another form of furnace used in the manufacture of spelter (Silesian), the workman after charging can leave the furnace until the time for tapping arrives. The two operations involve work for six hours a day only.

Dangers and Prevention.

—During distillation the detrimental effect of a current of air (formation of zinc oxide) on the zinc is an obstacle to the removal of the fume by exhaust ventilation locally applied over the prolongs of the condensers. Exhaust ventilation of a kind can, however, be arranged, except under unfavourable weather conditions, by erecting hoods of material such as galvanized iron right across the roof of the shed over, and parallel with, the furnaces, up which the heated current of air from the furnaces travels. Lofty, roomy sheds assist materially in the escape of the fumes. Various forms of modification in the condensers, designed to lessen escape of fume, and so recover more zinc, are being tried.

Samples of fume condensed as a grey powder, and collected by Collis from different kinds of prolongs, showed 1·3 to 2·7 per cent.[7] of metallic lead respectively, and a sample of dust deposited from material containing 10 per cent. of lead, 3·25 per cent.[8].

Manufacture of Red and Orange Lead and Litharge.

—These processes are frequently carried on as part of lead-smelting works. Red lead is produced by oxidation, first, of metallic pig-lead, in a reverberatory furnace at dull red heat, into massicot (yellow monoxide). During the process the material is constantly raked. The massicot is withdrawn from the furnace, and subsequently, after drying and sieving, is again subjected to similar treatment at slightly lower temperature. Orange lead is made by treating white lead in the manner described.

During the ten years 1900-1909 the number of reported cases from the manufacture of red lead was 108, of which 47 were attributed to work at the furnaces, 43 to packing and sieving, and 16 occurred among general labourers, part of whose duty it was to sweep up the floors. Collis estimates the attack rate in the five years 1905-1909, in a certain number of factories employing 171 persons, at 50 per 1,000. Reference to the table on p. 48 shows that the proportion of those suffering from encephalopathy is higher than in any other industry—an observation previously noted by Layet[9].

Dangers and Prevention.

—Danger is practically limited to escape of dust in (1) raking the charge out from the hearth on to iron trolleys, (2) sieving, and (3) packing. In all these operations exhaust ventilation is essential, and for sieving and packing the installation requires to be designed with especial care, so as to be able to keep within the sphere of the exhaust the spading and shovelling of the material, in very fine state of division, into the cask. Sometimes the material is elevated from pits, and eventually packed by mechanical means into barrels resting on a jolter. Unless the elevators are quite dust-proof, and the collar hermetically seals the connection of the shoot with the barrel, the vibration of the heavy machinery and pressure of air inside the casing will cause dust to escape.

Red lead can be, and is, now made on an extensive scale in such a way that all operations, from commencement with pig-lead to the final packing, are carried out by mechanical means so entirely closed in that the worker does not come into contact with the material. The person who then may be affected is the fitter attending to repairs of the machinery. The pig-lead is melted, stirred, and mixed in a covered-in melting-pot. The massicot which is formed is drawn off by an exhaust into a hopper, from the bottom of which it is fed mechanically on to the floor of the furnace. Mechanical rabbles stir it from the centre to the outside of the furnace floor, from where it is conveyed, under negative pressure, to the hopper of a grinding mill. From here it is again similarly fed into another furnace. The exhaust pipe from this furnace collects the finished product, carrying it mechanically to a hopper which automatically feeds the red lead into casks. Negative pressure throughout prevents escape of dust.

Manufacture of Litharge.

—Pig-lead is placed in a cupellation furnace, and constantly stirred and raked over to cause entire oxidation, and then is either raked out or run out from the furnace hearth into moulds, and allowed to cool in the form of large balls. These balls, of a roughly crystalline nature, are deposited on the floor, where they are exposed to the air. Disintegration is accelerated by breaking up the large fragments by hand. Subsequently the material is placed in a disintegrator for fine division and packed.

Dangers and Prevention.

—Manufacture of litharge may cause a greater amount of dust than any other process with which we are familiar. The nature of the operations is such that it is impossible at all stages to control this dust. Danger is greatest in the early operations of shovelling up the disintegrated powdery material from the floors into receptacles, and in discharging the contents into the disintegrating machine. The work is heavy, and a respirator is with difficulty worn. A movable hood attached to a flexible duct in connection with an exhaust which could be moved from place to place on the floor suggests itself, but when tried it has not effectively controlled the dust, owing to both the trouble involved and the difficulty of bringing the exhaust near enough to the work. When once the material reaches the disintegrator, exhaust over the hopper, and in connection with the enclosed sifter and grinder and packing machine, can readily be secured. Bins should be provided for the litharge lumps, so as to avoid trampling the powder underfoot, and covered barrows for removing the semi-powdered material. Alternation of employment lessens risk, and should be always arranged. In any new plant the possibility of automatic methods of carrying out the process as far as possible should be considered.

Sheet Lead and Lead Piping.

—This industry also is not infrequently carried out on smelting premises. To make lead piping, molten refined lead is run into a cylinder containing an adjustable mandrel in its centre. The cylinder is forced by hydraulic pressure against a hollow ram having an adjustable orifice to form the desired thickness of pipe. In the case of sheet lead the thick plates are gradually reduced to the desired thickness by pressure of heavy steel rollers.

Dangers and Prevention.

—Little risk attaches to handling the clean sheet lead or drawn lead. Danger is in the early stages. Old oxidized lead piping, lead cisterns, tea lead, old accumulator plates, etc., lie in heaps on the premises. These cannot be handled without generation of dust. When melted and stirred, copious fumes arise, carrying up dust, from which, and from that raised in drossing the surface of the metal, absorption of lead is inevitable unless the melting-pot is fully protected from side-draughts and provided with a hood and duct leading into the main chimney-stack. Doors in front of the hood serve still further to confine the fumes. The skimmings from the pot require to be placed in a receptacle under the hood. Of 109 cases reported in the ten years 1900-1909, operations at the melting-pot accounted for at least 47. We are in agreement with Dixon Mann, who remarks: “Workers in metallic lead do not suffer unless they are frequently in the presence of large quantities of the molten metal, or inhale fine particles of solid lead or its oxide whilst manipulating old metal. Lead, though not usually classed amongst the volatile metals, is capable of volatilization at a high temperature, and in the form of vapour may be taken into the system through the respiratory tract, and also into the stomach. One of the worst cases of chronic lead poisoning I ever saw was that of a man who bought the sheets of lead linings of old tea-chests, and melted them down into pig-lead. He did the work in a small room, without any contrivance for ventilation, and attended to the whole process himself”[10].

Letterpress Printing.

—In this industry account has to be taken of contact with—

1. Molten lead in (a) casting the type in different kinds of machines, including the monotype and linotype; (b) in stereotyping; and (c) in recasting into moulds the line or single type after it has been once used, together with débris from the stereo machine and sweepings from the floor.

2. Metallic lead in handling and dressing the type, and subsequent use of it by the compositor. The type metal itself usually consists of—Lead, 75 per cent.; antimony, 23 per cent.; and tin, 2 per cent.

During the ten years 1900-1909, 200 cases were reported—92 compositors, 71 stereotype and linotype operators, and 37 in subsidiary processes, mainly in the casting-room. Thus, apparently, operations involving contact with molten metal are more likely to cause lead poisoning than actual handling.

Type-Casting.

—In letter founding and in the monotype letter-casting machine the molten metal, heated by a coal fire in the former and Bunsen burner in the latter, at regular intervals fills the matrices at a point where it is cooled by a jet of compressed air, and the formed letter is then mechanically ejected into a receptacle. The temperature of the molten metal has to be carefully regulated, and does not usually rise above 400° to 450° C.—a temperature at which it is extremely doubtful if lead fume can be produced. Sommerfeld[11] states that in 60 cubic metres of air aspirated close to a type-casting machine no trace of lead was found, because vaporization does not take place below 550° C. Such skimming as must occasionally be made of the small surface of molten metal is in a slaggy state, and does not appear to contain much oxide. This is deposited usually in a small box and removed to be remelted once a day. What fume, often of unpleasant odour, is noted is probably due to acroleic acid vapour from the grease and dirt.

The letters having been cast, the type may be rubbed on sandstone or on a file, by which small quantities of metallic dust are given off; set up on setting-boards so that all letters face the same way (work on which female young persons are usually engaged); certain portions of letters undercut so as to make them lie perfectly parallel; dressed, planed, and examined, so as to be of precisely the same height; and finally assorted into founts and packed in the warehouse. In all these operations the fingers necessarily get blackened by contact, and there must be slight dislodgment of metal particles to account for the cases reported.

In the linotype machine, matrices are brought down from the magazine by touching the corresponding letters on the type indicator until they are arranged so as to form the line; a lever then carries them sideways into position, so as to allow the molten metal to flow into the mould and cast the line. Another lever then raises the matrices, which are carried into the magazine again, the slab of metal with the cast line upon it falling into a receptacle. Here, again, danger of lead fume is hardly in question. As the matrices drop down from the magazine, particles of lead which they have gathered when in contact with the metal are detached, and are visible on every linotype machine at this point. The brass cover of the magazine, if not frequently cleaned, soon becomes coated with fine dust. Although lead fume may not be given off, it is none the less necessary to remove the products of combustion from the heating apparatus, in order to prevent constant vitiation of air and to reduce the temperature in the neighbourhood of the machines. Monotype machines give off much heat. Exhaust ventilation by hoods reaching well over the pots, and branch ducts entering the main duct in connection with a fan tangentially, can alone accomplish this satisfactorily. Hoods and ducts leading merely into a shaft running up the side of the building fail to prevent condensation of the water vapour, which in consequence trickles back. Wherever a well-thought-out system of exhaust ventilation has been installed, reduction in temperature and comfort to the operatives has been secured. Temperatures above 65° F. must incommode a linotype operator.

In the foundry the recasting of old used type, etc., is effected, and periodically scraps and sweepings are melted down. These melting-pots should have telescopic hoods so balanced that they can readily be lowered, so as to enclose the bath of molten metal and allow the fume to be drawn by the fan into a duct of such width as to offer no obstacle to escape. A duct too narrow to deal with the great expansion the heated air undergoes is a defect very frequently found. A principal source of danger is the skimming of the melting-pot for sweepings, etc., and deposit of the large amount of dross by the side of the pot. Receptacles for the dross in connection with the exhaust system are imperatively needed.

Exhaust, where practicable, over the often large melting-pot for stereotype casting is desirable, in order to secure a reasonable temperature. Here there is the danger of splashing of molten metal, which is subsequently trodden underfoot.

Compositors’ Work.

—The letters are distributed in the small compartments of the type cases. From attrition dust may lie thick in the compartments, and when at work there is always tendency for small quantities of this dust to be dispersed. While this is the principal source of poisoning, inasmuch as dust containing lead must adhere to the fingers, lead may thus enter the system with food or when smoking. It is quite as easy, also, to believe that lead poisoning may result from solvent action of the blood and tissue fluids on small spicules of lead type which penetrate the skin as to credit the well-substantiated cases of plumbism ensuing on retention of bullets or shot in the body. Compositors sometimes contract the habit of holding type between their teeth.

The old dangerous method of blowing out the dust on the staircase by means of a bellows should before long be entirely supplanted by use of suction bellows or use of printers’ case dust-extractors. In the Clements apparatus the cases are placed on a shelf, which is made to oscillate; air is forced into the compartments from numerous jets, so as to raise the dust, which is removed by suction and collected. The cases are thus cleaned with great saving of time in the composing-room itself, and without contamination of the general atmosphere by dust.

The dust removed from a composing box by a vacuum cleaner was found in the Government laboratory to contain 9·8 per cent. of metallic lead, and that collected from the top of the magazine of a linotype machine 8·18 per cent.

Regulations issued in 1911 in Austria require, among other things—(1) Melting-pots, and, so far as is practicable, linotype pots also, to be provided with hoods and ducts to carry the fumes to the outside air or into a chimney; (2) the type cases to fit either close on to the floor or with a sufficient space below the lowest drawer to enable the floor underneath to be easily cleaned; (3) the interior of all compositors’ boxes to be cleaned at least once every three months—if possible, by means of a vacuum suction apparatus; and (4) quarterly periodical medical examination to be made of persons employed in casting, stereotyping, linotyping, assorting type, and composing.

Sommerfeld[12] believes that in Berlin 1·07 per cent. of the compositors suffer from lead poisoning every year, and that 2·5 per cent. of all the diseases they suffer from are due to lead. Among 3,641 printers applying for sick relief, Silberstein[13] found 65 suffering from lead poisoning (1·7 per cent.). Where, however, diagnosis of lead poisoning is based upon examination of the blood, as in Leipzig, the amount of compensation paid by the Sickness Insurance Society has diminished considerably. Thus, of 207 compositors who were either sent by medical men as cases of, or went themselves suspecting that they were suffering from, lead poisoning, only 17 (8·2 per cent.) showed basophilia to such degree as to warrant the diagnosis. The proportion, on the other hand, among letter founders and electrotypers was 28·6 per cent.

Printers suffer extensively from phthisis, their comparative mortality from this cause as compared with the figure for all occupied males being 290 : 175[14]. This high mortality is probably due mainly to the vitiation of the atmosphere, and reluctance, on account of extreme sensitiveness to draughts, to admit fresh air. This closing of windows by persons employed should be an additional reason for checking the vitiation from Bunsen burners in connection with linotype and monotype machines by the only practicable means of preventing perceptible draught—namely, exhaust ventilation.

File-Cutting.

[15]—The steel file to be cut is placed on a stone block in the centre of which is inserted a smaller steel block, called a “stiddy.” The worker holds in his right hand a hammer, weighing sometimes 7 or 8 pounds, and in his left, closely gripped, a chisel. Each tooth in the file—and there may be as many as 3,800 teeth to be cut—is the result of a blow on the chisel, and we have counted as many as 120 blows with a 7-pound and 200 with a 4-pound hammer per minute. To offer resistance to the blow and yet prevent a recoil, the file (in the case of the finer kinds) is placed on a lead bed—that is, a thin strip of metallic lead. With attrition from repeated impact the lead bed becomes worn away in the course of a few days, and part of what is so worn away necessarily takes the form of lead in fine particulate state.

Dangers.

—Absorption of lead follows from the dust generated by each blow, from brushing the dust off the cut file, and from licking the finger and thumb holding the chisel. Other conditions predisposing to plumbism before the present regulations came into force, and not altogether without effect still, were—too close proximity of one stock to another, defective ventilation of the (frequently) small shed in which the work was done, overcrowding, accumulation of dust on the benches, uneven floors, inadequate washing facilities, and, apparently, lack of appreciation of the danger.

The remarkable feature of plumbism in this industry is the long duration of employment before pronounced symptoms manifest themselves (see p. 51). The insidious onset is, however, accompanied by an undermining of the constitution, showing itself eventually in atrophy of the muscles, especially of the thenar and hypothenar eminences of the hand, and of the lumbricals and interosseous muscles of the fingers, the result of continual gripping of the hammer and chisel, chronic interstitial nephritis, with its associated arterio-sclerotic changes, and heavy incidence of phthisis.

Provision of locally applied exhaust ventilation has never been suggested for this industry, owing to absence of power to drive a fan in the small workshops, and because no lead dust is seen to be given off. Diminution in the number of cases is due to the fact that machine file-cutting (with zinc as the bed) has been substituted for hand file-cutting for coarse files. In hand cutting, in some instances, beds of pewter, or of alloys with comparatively small proportion of lead, have replaced the use of lead beds. The remedial measures prescribed in the regulations have also played a part.

At the time the regulations came into force, in 1903, there were about 708 file-cutting shops in the United Kingdom, of which 517 were in Sheffield. Immediately after they came into force 126 certificates of exemption were granted for use of beds containing less than 5 per cent. of lead, and every year fresh applications are received[16]. There does appear, however, to be difficulty in securing beds which conform to the standards laid down. Thus, in the four years 1907-1910, of 23 samples submitted as containing less than 5 per cent., 16 were in excess.

The number of reported cases of poisoning in the five years 1900-1904 was 151, and 51 in the five later years 1905-1909. The attack rate is about 10 per 1,000, but, although this may be low compared with other trades, the much greater severity of the attacks has to be borne in mind.

File-Hardening.

—The process consists in keeping the files in a bath of molten lead at high temperature, covered with charcoal. The file is removed when red-hot, straightened if necessary, and plunged into a solution of brine.

Dangers and Prevention.

—Poisoning is attributable to fume given off by the molten lead (a temperature of 850° C. was recorded by S. R. Bennett—see p. 201), risk of which can only be met by efficient hooding and exhaust unless an alternative method of hardening is adopted, dispensing with the lead bath—e.g., by exposure to heat on a hearth, in a gas furnace, or by other means. In this small industry in and around Sheffield three cases were reported within a year, each involving partial or complete paralysis of the extensors of the forearm. Of ten men employed at the work, three showed presence of a blue line, three were cachectic, and one had weakness of the arms and wrists. In two of the three factories attempts had been made unsuccessfully to carry the fumes away by a hood and duct[17].

Hardening of forks and similar articles in the same manner has also given rise to poisoning.

We are informed that methods of hardening and tempering drills, tools, etc., by the use of fused metallic salts, are being adopted in some works. By mixing together two or more salts in definite proportions, suitable fusing-points can in all cases be produced. These baths can be raised to any desired melting-point to suit the requirement of different steels. For example, sodium nitrate and potassium nitrate in certain proportions give melting-points from 220° to 340° C., and can be used for tempering baths up to 600° C. For tempering above 600° C. mixtures of sodium chloride and potassium chloride can be used, whilst for hardening, sodium chloride or barium chloride give adequate ranges of temperature. Similarly, mixtures of sodium sulphate (melting-point, 890° C.) and lithium sulphate (860° C.) can be made to give any melting-point from 605° to 860° C.

Tinning of Metals.

[18]—Cheap hollow-ware vessels such as kettles and frying-pans are often coated with a mixture of (usually) half lead and half tin by dipping them into a bath of the molten metal, after cleaning in hydrochloric acid.

Danger and Prevention.

—Duckering has shown (see p. 203) that fumes of chloride of lead are given off which are especially noticeable when the dipped article is removed to a stand to have the superfluous metal wiped from it with tow while still in a molten state. Detailed reference is made on p. 204 to the nature of the fume given off and the amount of lead present in the atmosphere breathed and inhaled daily by the worker.

The danger from fumes can be in great measure removed, both from the bath and from the wiping stand, by locally applied exhaust ventilation, which may be secured by utilization of the draught from the fire under each melting-pot, or by a hood and duct carried vertically through the roof if arranged as described on p. 209. Danger from dust arises also from the skimmings, if not deposited in a receptacle within the hood, from dust and débris on the floor, and possibly from traces of metallic lead and lead chloride attached to particles of tow floating in the air. Risk of lead absorption is less in later processes, such as affixing the spout and handle (mounting), and hammering or denting. Occasionally roughnesses are removed by rubbing the coating with emery paper.

Harness Furniture.

—Hames, buckles, bits, etc., are usually coated with nickel or copper, more rarely with silver. The process is in the nature of soldering, and the steel, prepared in the same way as has been described for hollow-ware, has a mixture of two parts tin and one part lead poured over it on a hearth. The strip of thin nickel sheeting is passed through a similar mixture, and is wiped with tow—the operation to which such poisoning as occurs in this industry is mainly due, in consequence of the difficulty of efficiently removing the vapour of lead chloride from the molten metal upon the long strip of nickel. Subsequently the prepared steel article and the strip of nickel or copper are made to unite under pressure of a soldering-iron. In silver plating danger from fume is slightly less, as the steel portion (for example, the hame) only is tinned. In the final operation of polishing on a mop danger arises from dust, unless locally applied exhaust is provided.

Iron Drums and Kegs.

—Use of a tinning mixture of lead and tin in this industry is obviously in the nature of soldering. The body of the drum is made either of black sheet-iron or of terne (lead-coated) sheet. In order to unite the seam and to fix the bottom sheet, the drum is made to stand in a shallow bath and laid on its side. The danger from lead chloride vapour is considerable, and the method of prevention is precisely of the kind described above.

Similar coating of articles first cleaned in hydrochloric acid is met with, as, for example, of the component parts of radiators of motor-cars, of steel bars, and of wire. Incidence of poisoning has not occurred to an extent to make necessary more than the application of locally-applied exhaust to remove the fumes.

Manufacture of Terne Plates.

—The manufacture of lead-coated sheets for roofing purposes is carried on in a few works in South Wales along with the manufacture of tin plates. Lead poisoning in the industry is practically unknown. We can only recollect occurrence of one case, despite the fact that the mixture contains from 65 to 95 per cent. of lead. For cleaning the plates prior to passing them through the concentrated zinc chloride flux into the molten mixture, dilute sulphuric acid is used, and not hydrochloric acid. As to the remarkably different results on health of the two processes, Duckering concludes:

“The absence of lead poisoning among terne-plate workers and tinners would appear to be explained by—(1) The use of cleaning agents and a flux of such a nature, and in such a way, as to involve a minimum contact with the tinning metals, and under such conditions as to inhibit extensive interaction between them, and also under such conditions as to inhibit production of fume or vapours, even if any interaction occurs; (2) use of a scientifically prepared flux containing no uncombined acid or excess of water in such a way as to prevent introduction of these substances, or of ferrous compounds coming into intimate contact with the tinning metal; (3) so conducting the operation of tinning that any chlorides possibly adhering to the plates are removed before the plate reappears in the open air, under conditions preventing them from appearing in the air as vapour, but it is very doubtful whether any chlorides could adhere to the plates; and (4) absence of any manual work on the plates before the metallic coating is set and hard. On the other hand, the existence of widespread lead poisoning in tinning of hollow-ware is explained by—(1) Use of cleaning agents and flux in such a way as to bring these materials into intimate contact with the tinning metals under conditions eminently favourable to chemical interaction and vaporization of resultant compounds; (2) use of an unscientifically prepared flux containing a large excess of water and much free acid; (3) so conducting the operations as to favour the escape into the atmosphere of vapours of soluble lead compounds, such as lead chloride, and of metallic lead and soluble lead compounds, carried mechanically by fibres of tow during processes subsequent to tinning, as in wiping; and (4)—a minor point not to be lost sight of—possibility of contamination of the hands by soluble lead compounds, due to manipulating the material with which the articles are wiped.

“It should be added that while use of a scientifically prepared flux [(2) above] in hollow-ware tinning would no doubt lessen the possibility of the production of fumes, it is not to be anticipated (unless a flux containing no chlorides were used) that this would do away with lead poisoning. In other words, the method of use is, as indicated above, a far more important factor.”

In the ten years 1900-1909 the number of reported cases in tinning hollow-ware was 93 among about 200 persons employed, in harness furniture 23 among about 150 persons employed, and in iron drums and kegs 47 among about 250 persons employed.

Plumbing and Soldering.

—The figures included in the table on p. 47 have reference only to these processes as carried on in factory premises. House plumbers, when reported, are included with house painters. The figures are made up of two classes—(1) Those handling white and red lead paste, and (2) those engaged in soldering and lead burning. The number of cases reported in the ten years 1900-1909 was, in the first class 122, and in the second 95.

Any worker using red lead as a jointing paste who is not a house plumber or a coach or ship builder is included under the first heading, as, for example, electricians, persons engaged in mechanics’ workshops, lead-light making where red lead cement is brushed between the lead lines and the glass to render them water-tight, and such occupations as placing strips of canvas coated with red lead between sheets of iron work before riveting, so as to afford protection against rust. In several reports there is reference to the dust created in the breaking up of old joints with aid of hammer and chisel before proceeding to recaulk them.

Dust in making up the paste is the principal source of danger. This is crudely done, and unless large quantities of paste are made exhaust ventilation is never provided, in view of the intermittency of the work. The wearing of a respirator should be possible, but it would be unsafe to recommend that as a sufficient means of prevention. Installation, whenever possible, of localized exhaust ventilation at the mixing bench is most desirable. Personal cleanliness is important, as the hands become ingrained with the paste.

The heading “Soldering” includes in the main (a) the soldering of tins of all descriptions, bicycle lamps, etc., with a stick of solder, either held in the hand or lying on the bench, which is touched by the hot soldering-iron, the surface to be soldered having previously been cleaned with “killed spirit”—i.e., zinc chloride flux; and (b) lead burning, by means of a hydrogen or oxy-hydrogen blowpipe flame, of lead-lined boxes, vats in sulphuric acid and other chemical works. Some cases are included which occurred in the manufacture of solder itself. Green wood is held at the bottom of the pot of molten metal, and the gases distilled from the wood pass upwards through the metal and escape at the surface, carrying small quantities of lead into the atmosphere of the workroom.

Dangers and Prevention.

—It can be confidently said of soldering that, bearing in mind the very large number of persons employed, the number of cases reported is remarkably small, and it is difficult to assert generally, as can easily be asserted of tinning, that inhalation of soldering fumes must necessarily set up lead poisoning. Moreover, examination of persons employed in soldering for signs of lead absorption is almost always negative, a blue line on the gums even being rarely visible.

On the other hand, the process of soldering is so analogous to that of tinning that such poisoning as occurs is probably due to inhalation by susceptible persons of lead chloride fumes. And this is borne out by the results of analysis in the Government laboratory of a sample of deposit collected from a duct where exhaust ventilation had been applied to take away the fumes.