benzine precedes treatment with acid.
A further source of artificial manure is _basic slag_—the slag left in
the manufacture of steel by the Gilchrist-Thomas method—which contains
10-25 per cent. of readily soluble phosphoric acid. It requires,
therefore, only to be ground into a very fine powder to serve as a
suitable manure.
Owing to the considerable heat generated by the action of the sulphuric
acid when mixed with the pulverised raw materials (especially in the
conversion of the phosphorites) hydrofluoric and silicofluoric acid
vapours are evolved in appreciable amount, and also carbonic and
hydrochloric acid vapours, sulphur dioxide, and sulphuretted hydrogen
gas. These gases—notably such as contain fluorine—if not effectually
dealt with by air-tight apparatus and exhaust ventilation—may lead to
serious annoyance and injury to the persons employed. Further, there is
risk of erosion of the skin from contact with the acid, &c.
A case is described of pustular eczema on the scrotum of a worker engaged
in drying sodium silicofluoride, due probably to conveyance of irritating
matter by the hands. After the precaution of wearing gloves was adopted
the affection disappeared.
A marked case of poisoning by nitrous fumes even is recorded in the
manufacture of artificial manure from mixing Chili saltpetre with a very
acid superphosphate.
Injurious fumes can be given off in the rooms where bones are stored and,
in the absence of efficient ventilation, carbonic acid gas can accumulate
to an amount that may be dangerous.
The fine dust produced in the grinding of _basic slag_ has, if inhaled, a
markedly corrosive action on the respiratory mucous membrane attributed
by some to the high proportion (about 50 per cent.) in it of quicklime.
As a matter of fact numerous small ulcers are found on the mucous
membranes of basic slag grinders and ulceration of the lung tissue has
been observed. The opinion is expressed that this is due to corrosive
action of the dust itself, and not merely to the sharp, jagged edged
particles of dust inhaled. And in support of this view is cited the
frequency with which epidemics of pneumonia have been noted among
persons employed in basic slag works. Thus in Nantes thirteen cases of
severe pneumonia followed one another in quick succession. And similar
association has been noted in Middlesbrough, where the action of the
basic slag dust was believed to injure the lung tissue and therefore to
provide a favourable soil for the development of the pneumonia bacillus.
Statistics collected by the Imperial Health Office showed that in the
three years 1892, 1893, and 1894, 91·1 per cent., 108·9 per cent., and
91·3 per cent. respectively of the workers became ill, the proportion
of respiratory diseases being 56·4 per cent., 54·4 per cent., and 54·3
per cent. respectively. A case of severe inflammation of the lungs is
described in a labourer scattering basic slag in a high wind which drove
some of it back in his face.
Lewin has described a case in which a worker scattering a mixture of
basic slag and ammonium superphosphate suffered from an eczematous
ulceration which, on being scratched by the patient, became infected and
led to death from general blood poisoning. Lewin regarded the fatal issue
as the sequela of the scattering of the manure.
Inflammation of the conjunctiva and of the eyelids has been recorded.
CHROMIUM COMPOUNDS AND THEIR USES
Chrome ironstone, lime, and soda are ground and intimately mixed. They
are next roasted in reverberatory furnaces, neutral _sodium chromate_
being formed. This is lixiviated and converted into sodium bichromate
(Na₂Cr₂O₇) by treatment with sulphuric acid. Concentration by evaporation
follows; the concentrated liquor is crystallised in cast-iron tanks. The
crystals are centrifugalised, dried, and packed. _Potassium bichromate_
may be made in the same way, or, as is usually the case, out of sodium
bichromate and potassium chloride.
The bichromates are used in the preparation and oxidation of chrome
colours, but their principal use is in dyeing and calico printing,
bleaching palm oil, purifying wood spirit and brandy, in the preparation
of ‘Swedish’ matches, in the manufacture of glass, in photography, in
dyeing, in tanning, and in oxidation of anthracene to anthraquinone.
Lead Chromate and Chrome Colours
_Chrome yellow_ is neutral lead chromate (PbCrO₄). It is obtained by
precipitating a solution of potassium bichromate with lead acetate or
lead nitrate, or by digesting the bichromate solution with lead sulphate,
and is used as a paint and in calico and cloth printing. With Paris or
Berlin blue it forms a _chrome green_. _Chrome orange_, i.e. basic lead
chromate (PbCrO₄Pb(OH)₂) is made by adding milk of lime to lead chromate
and boiling.
_Chromium_ and _chromic acid salts_ are widely used in dyeing and
printing, both as mordants and oxidising agents and as dyes (chrome
yellow, chrome orange). In mordanting wool with potassium chromate the
wool is boiled in a potassium chromate solution to which acids such as
sulphuric, lactic, oxalic, or acetic are added.
In dyeing with chrome yellow, for instance, the following is the process.
Cotton wool is saturated with nitrate or acetate of lead and dried,
passed through lime water, ammonia, or sodium sulphate, and soaked in a
warm solution of potassium bichromate. The yellow is converted into the
orange colour by subsequent passage through milk of lime.
_Chrome tanning._—This method of producing chrome leather, first patented
in America, is carried out by either the single or two bath process.
In the two bath process the material is first soaked in a saturated
solution of bichromate and then treated with an acid solution of
thiosulphate (sodium hyposulphite) so as to reduce completely the chromic
acid. The process is completed even with the hardest skins in from two to
three days.
In the single bath method basic chrome salts are used in highly
concentrated form. The skins are passed from dilute into strong
solutions. In this process also tanning is quickly effected.
EFFECTS ON HEALTH.—Among the persons employed in the bichromate factory
of which Leymann has furnished detailed particulars, the number of sick
days was greater than that among other workers.
Further, _erosion of the skin_ (_chrome holes_) is characteristic of
the manufacture of bichromates. These are sluggish ulcers taking a long
time to heal. This is the main cause of the increased general morbidity
that has been observed. The well-known perforation of the septum of the
nose without, however, causing ulterior effects, was observed by Leymann
in all the workers in the factory. This coincides with the opinion of
others who have found the occurrence of chrome holes, and especially
perforation of the septum, as an extraordinarily frequent occurrence.
Many such observations are recorded,[1] and also in workers manufacturing
‘Swedish’ matches. Thus of 237 bichromate workers, ulcers were present
in 107 and perforation in 87. According to Lewin, who has paid special
attention to the poisonous nature of chromium compounds, they can act in
two ways: first, on the skin and mucous membrane, where the dust alights,
on the alimentary tract by swallowing, and on the pharynx by inhalation.
Secondly, by absorption into the blood, kidney disease may result.
The opinion that chromium, in addition to local, can have constitutional
effect is supported by other authorities. Leymann describes a case
of severe industrial chrome poisoning accompanied by nephritis in a
worker who had inhaled and swallowed much chromate dust in cleaning
out a vessel. Regulations for the manufacture of bichromates (see Part
III) have no doubt improved the condition, but reports still show that
perforation of the septum generally takes place.
It must be borne in mind that practically all chromium compounds are not
alike poisonous. Chrome ironstone is non-poisonous, and the potassium
and sodium salts are by far the most poisonous, while the neutral
chromate salts and chromic oxide are only slightly so. Pander found that
bichromates were 100 times as poisonous as the soluble chromium oxide
compounds, and Kunkel is of opinion that poisonous effect shown by the
oxides is attributable to traces of oxidation into chromic acid.
Lewin, on the other hand, declares in a cautionary notice for chrome
workers generally that all chromium compounds are poisonous, and
therefore all the dyes made from them.[2]
In the manufacture of bichromates, chance of injury to health arises
partly from the dust, and partly from the steam, generated in pouring
water over the molten mass. The steam carries particles of chromium
compounds with it into the air. In evaporating the chromate solutions,
preparation of the bichromate, breaking the crystals, drying and packing,
the workers come into contact with the substance and the liquors. Chrome
ulceration is, therefore, most frequently found among those employed in
the crystal room and less among the furnace hands.
From 3·30 to 6·30 mg. of bichromate dust have been found in 1 c.m. of air
at breathing level in the room where chromate was crushed, and 1·57 mg.
where it was packed. Further, presence of chromium in the steam escaping
from the hot chrome liquors has been proved.[3]
Poisoning from use of chrome colours is partly attributable to lead, as,
for example, in making yellow coloured tape measures, yellow stamps, and
from the use of coloured thread. Gazaneuve[4] found 10 per cent. of lead
chromate in such thread, in wool 18 per cent., and in the dust of rooms
where such yarn was worked up 44 per cent.
Use of chrome colours and mordants is accompanied by illness which
certainly is referable to the poisonous nature of the chrome. In France
use of chromic and phosphoric acid in etching zinc plates has caused
severe ulceration.
Bichromate poisoning has been described among photographers in Edinburgh
in the process of carbon printing, in which a bichromate developer is
used.[5]
There is much evidence as to occurrence of skin eruptions and
development of pustular eczema of the hands and forearms of workers in
chrome tanneries.[6] In a large leather factory where 300 workers were
constantly employed in chrome tanning nineteen cases of chrome ulceration
were noted within a year. Injury to health was noted in a chrome tannery
in the district of Treves, where the two bath process was used, from
steam developed in dissolving the chromate in hot water.
Finally, I have found several records in 1907 and 1908 of perforation of
the septum in Bohemian glass workers.
MANGANESE COMPOUNDS
The raw material of the manganese industry is _hausmannite_ (manganese
dioxide, MnO₂). This is subjected to a crushing process, sorted, sieved,
finely ground, washed, and dried. The pure finely ground manganese
dioxide is much used in the chemical industry, especially in the
recovery of chlorine in the Weldon process and in the production of
_potassium permanganate_, which is obtained by melting manganese dioxide
with caustic soda and potassium chlorate or nitre, lixiviation and
introduction of carbonic acid, or better by treatment with ozone.
Manganese is also used in the production of colours: the natural and
artificial umbers contain it; in glass works it is used to decolourise
glass, and also in the production of coloured glass and glazes; in the
manufacture of stove tiles, and in the production of driers for the
varnish and oil industry. Manganese and compounds of manganese are
dangerous when absorbed into the system as dust.
Already in 1837 nervous disorders had been described in workmen who
ground manganese dioxide.[1] The malady was forgotten, until Jaksch[2]
in Prague in 1901 demonstrated several such cases in persons employed
in a large chemical factory in Bohemia, from the drying of Weldon mud.
In the same year three similar cases were also described in Hamburg.[3]
In 1902 Jaksch observed a fresh case of poisoning, and in the factory
in question described a condition of manganophobia among the workers,
obviously hysterical, in which symptoms of real manganese poisoning were
simulated. In all some twenty cases are known. Jaksch is of opinion that
it is manganese dust rich in manganese protoxide that is alone dangerous,
since, if the mud has been previously treated with hydrochloric acid, by
which the lower oxides are removed, no illness can be found. The most
dangerous compounds are MnO and Mn₃O₄.
PETROLEUM
OCCURRENCE AND USES.—Crude petroleum flows spontaneously from wells in
consequence of high internal pressure of gas or is pumped up. In America
and Russia also it is conveyed hundreds of miles in conduits to the ports
to be led into tank steamers.
The crude oil is a dark-coloured liquid which, in the case of
Pennsylvanian mineral oil, consists mainly of a mixture of hydrocarbons
of the paraffin series, or, in Baku oil, of those of the naphtha series.
There are in addition sulphur compounds, olefines, pyridin, &c. The
crude oil is unsuitable for illuminating purposes and is subjected to a
distillation process. It is split up into three fractions by a single
distillation, namely, (_a_) benzines (boiling-point 150° C.), (_b_)
lighting oil (boiling-point 150°-300° C.); at a temperature of 300° C.
the distillation is stopped so that (_c_) the residuum boiling above 300°
C. remains. Distillation is effected (in America) in large stills, in
which periodically benzine and lighting oil up to 300° C. is distilled
and the residuum run off. In Baku continuously working batteries of
so-called cylindrical boilers are used, into which the crude oil
streams. In the first set of boilers, the temperature in which rises to
150° C., the benzine is distilled off, and in the succeeding ones, heated
to 300° C., the illuminating petroleum oils (kerosine), the residuum
flowing continually away.
The _mineral oil residues_ are used as fuel. Heating by this means,
tried first only in Russia, is spreading, especially for the heating of
boilers, in which case the liquid fuel is blown in generally as a spray.
The combustion if rightly planned is economical and almost smokeless.
The American oil residuum, rich in paraffin, is distilled, the distillate
is cooled and separated by pressure into solid paraffin and liquid oil.
The latter and the Russian mineral oil residues which are free from
paraffin are widely used as lubricants. In the production of lubricants
the residues are distilled at low temperature (in vacuo or by aid of
superheated steam) and separated into various qualities by fractional
cooling, are then purified with sulphuric acid, and finally washed with
caustic soda solution.
In the preparation of vaseline the residum is not distilled, but purified
only with fuming sulphuric acid and decolourised with animal charcoal.
The _illuminating oil_ is next subjected to a purifying process
(refining); it is first treated with sulphuric acid and well agitated
by means of compressed air. The acid laden with the impurities is drawn
off below, and the oil freed from acid by washing first with caustic
soda and subsequently with water. It is then bleached in the sun. For
specially fine and high flash point petroleum the oil undergoes a further
distillation and purification with acid.
The fractions of crude petroleum with low boiling-point (under 150° C.)
are known commercially as raw _benzine_ or _petrol naphtha_. It is used
for cleaning, in extraction of fats and oils, and for benzine motors.
Frequently raw benzine is subjected to a purifying process and to
fractional distillation. Purification is carried out by means of
sulphuric acid and soda liquor and subsequent separation into three
fractions and a residue which remains in the retort—(_a_) _petroleum
ether_ (called gasoline, canadol, and rhigoline), which comes over
between 40° and 70° C., and serves for carburetting water gas and other
similar gases, as a solvent for resin, oil, rubber, &c.; (_b_) _purified
benzine_ (70°-120° C.) is used as motor spirit and in chemical cleaning;
(_c_) _ligroine_ (120°-135° C.), used for illuminating purposes; and
(_d_) the _residual oil_ (above 135° C.) serves for cleaning machinery
and, especially, as a solvent for lubricating oil, and instead of
turpentine in the production of lacquers, varnishes, and oil colours.
In _chemical cleaning_ works benzine is used in closed-in washing
apparatus, after which the clothes are centrifugalised and dried. In
view of the risk of fire in these manipulations, originating mainly from
frictional electricity, various substances are recommended to be added
to the benzine, of which the best known is that recommended by Richter,
consisting of a watery solution of oleate of sodium or magnesium.
EFFECTS ON HEALTH.—Industrial poisoning in the petroleum industry is
attributable to the gases given off from crude petroleum or its products
and to inhalation of naphtha dust. Poisoning occurs principally in
the recovery of petroleum and naphtha from the wells, in storage and
transport (in badly ventilated tanks on board ship, and in entering
petroleum tanks), in the refinery in cleaning out petroleum stills and
mixing vessels, and in emptying out the residues. Further cases occur
occasionally from use of benzine in chemical cleaning.
In addition to poisoning the injurious effect of petroleum and its
constituents on the skin must be borne in mind. Opinion is unanimous
that this injurious action of mineral oil is limited to the petroleum
fractions with high boiling-point and especially petroleum residues.
Statistics officially collected in Prussia show the general health of
petroleum workers to be favourable. These statistics related to 1380
persons, of whom forty-three were suffering from symptoms attributable
to their occupation. Of these forty-three, nine only were cases of
poisoning, the remainder being all cases of petroleum acne.
The conditions also in French refineries from statistics collected in
the years 1890-1903 seem satisfactory. Eighteen cases of petroleum acne
were reported, eleven of which occurred at the paraffin presses, five in
cleaning out the still residues, and two were persons filling vessels.
The conditions are clearly less favourable in the Russian petroleum
industry.[1]
The workers at the naphtha wells suffer from acute and chronic affections
of the respiratory organs. Those suffer most who cover the wells with
cast iron plates to enable the flow of naphtha to be regulated and led
into the reservoirs. In doing this they inhale naphtha spray.
Lewin[2] describes cases of severe poisoning with fatal issue among
American workers employed in petroleum tanks. One man who wished to
examine an outlet pipe showed symptoms after only two minutes. Weinberger
describes severe poisoning of two workers engaged in cleaning out a
vessel containing petroleum residue.
Interesting particulars are given of the effect of petroleum emanations
on the health of the men employed in the petroleum mines of Carpathia,
among whom respiratory affections were rarely found, but poisoning
symptoms involving unconsciousness and cerebral symptoms frequently.
These experiences undoubtedly point to differing physiological effects of
different kinds of naphtha.
This is supported by the view expressed by Sharp in America that
different kinds of American petroleum have different effects on the
health of the workers, which can be easily credited from the different
chemical composition of crude naphthas. Thus in Western Virginia, where a
natural heavy oil is obtained, asphyxia from the gas is unknown, although
transient attacks of headache and giddiness may occur, whereas in Ohio,
where light oils are obtained, suffocative attacks are not infrequent.
And it is definitely stated that some naphtha products irritate the
respiratory passages, while others affect the central nervous system.[3]
The authors mentioned refer to occurrence of cases of poisoning in the
refining of naphtha from inhalation of the vapour of the light oils
benzine and gasoline. Fatal cases have been recorded in badly ventilated
workrooms in which the products of distillation are collected. Workers
constantly employed in these rooms develop chronic poisoning, which is
reported also in the case of women employed with benzine. Intoxication is
frequently observed, it is stated, among the workmen employed in cleaning
out the railway tank waggons in which the mineral oils and petroleum are
carried.
Foulerton[4] describes severe poisoning in a workman who had climbed into
a petroleum reservoir, and two similar cases from entering naphtha tanks
are given in the Report of the Chief Inspector of Factories for 1908. Two
fatal cases are reported by the Union of Chemical Industry in Germany
in 1905 in connection with naphtha stills. Such accidents are hardly
possible, except when, through insufficient disconnection of the still
from the further system of pipes, irrespirable distillation gases pass
backwards into the opened still where persons are working. Ordinary cocks
and valves, therefore, do not afford sufficient security. Thus, several
workers engaged in repairing a still were rendered unconscious by gases
drawn in from a neighbouring still, and were only brought round after
oxygen inhalation.
Gowers describes a case of chronic poisoning following on frequent
inhalation of gases given off from a petroleum motor, the symptoms
being slurring speech, difficulty of swallowing, and weakness of the
orbicularis and facial muscles. Gowers believed this to be petroleum
gas poisoning (from incomplete combustion), especially as the symptoms
disappeared on giving up the work, only to return on resuming it again.[5]
Girls employed in glove cleaning and rubber factories are described as
having been poisoned by benzine.[6] Poisoning of chauffeurs is described
by several writers.[7]
Recent literature[8] tends to show marked increase in the number of
cases of poisoning from greater demand for benzine as a motive power for
vehicles. Such cases have been observed in automobile factories, and are
attributable to the hydrocarbons of low boiling-point which are present
as impurities in benzine.
A worker in a paraffin factory had entered an open benzine still to
scrape the walls free of crusts containing benzine. He was found
unconscious and died some hours later. It appeared that he had been in
the still several hours, having probably been overcome to such an extent
by the fumes as to be unable to effect his escape.
Attempt to wipe up benzine spilt in the storage cellar of a large
chemical cleaning works resulted in poisoning.
A night worker in a bone extracting works having turned on the steam,
instead of watching the process fell asleep on a bench. In consequence
the apparatus became so hot that the solder of a stop valve melted,
allowing fumes to escape. The man was found dead in the morning. In a
carpet cleaning establishment three workers lost consciousness and were
found senseless on the floor. They recovered on inhalation of oxygen.
One further case reported from the instances of benzine poisoning
collected recently[9] is worth quoting. A worker in a chemical factory
was put to clean a still capable of distilling 2500 litres of benzine.
It contained remains of a previous filling. As soon as he had entered
the narrow opening he became affected and fell into the benzine; he
was carried unconscious to the hospital, his symptoms being vomiting,
spastic contraction of the extremities, cyanosis, weak pulse, and loss of
reflexes, which disappeared an hour and a half later.
The occurrence of skin affections in the naphtha industry has been noted
by several observers, especially among those employed on the unpurified
mineral oils. Eruptions on the skin from pressing out the paraffin and
papillomata (warty growths) in workers cleaning out the stills are
referred to by many writers,[10] Ogston in particular.
Recent literature refers to the occurrence of petroleum eczema in a
firebrick and cement factory. The workers affected had to remove the
bricks from moulds on to which petroleum oil dropped. An eczematous
condition was produced on the inner surface of the hands, necessitating
abstention from work. The pustular eczema in those employed only a short
time in pressing paraffin in the refineries of naphtha factories is
referred to as a frequent occurrence. Practically all the workers in
three refineries in the district of Czernowitz were affected. The view
that it is due to insufficient care in washing is supported by the report
of the factory inspector in Rouen, that with greater attention in this
matter on the part of the workers marked diminution in its occurrence
followed.
SULPHUR
RECOVERY AND USE.—Sulphur, which is found principally in Sicily (also in
Spain, America, and Japan), is obtained by melting. In Sicily this is
carried out in primitive fashion by piling the rock in heaps, covering
them with turf, and setting fire to them. About a third of the sulphur
burns and escapes as sulphur dioxide, while the remainder is melted and
collects in a hole in the ground.
The crude sulphur thus wastefully produced is purified by distillation in
cast-iron retorts directly fired. It comes on the market as stick or roll
sulphur or as flowers of sulphur.
Further sources for recovery of sulphur are the Leblanc soda residues
(see Soda Production), from which the sulphur is recovered by the
Chance-Claus process, and the gas purifying material (containing up to 40
per cent.), from which the sulphur can be recovered by carbon bisulphide
(see Illuminating Gas Industry).
The health conditions of the Sicilian sulphur workers are very
unsatisfactory, due, however, less to the injurious effect of the
escaping gases (noxious alike to the surrounding vegetation) than to the
wretched social conditions, over exertion, and under feeding of these
workers.
Of importance is the risk to health from sulphuretted hydrogen gas,
from sulphur dioxide in the recovery of sulphur from the soda residues,
and from carbon bisulphide in the extraction of sulphur from the gas
purifying material.
SULPHURETTED HYDROGEN GAS
Sulphuretted hydrogen gas is used in the chemical industry especially
for the precipitation of copper in the nickel and cobalt industry, in
de-arsenicating acid (see Hydrochloric and Sulphuric Acids), to reduce
chrome salts in the leather industry, &c. In addition it arises as a
product of decomposition in various industries, such as the Leblanc soda
process, in the preparation of chloride of antimony, in the decomposition
of barium sulphide (by exposure to moist air), in the treatment of gas
liquors, and in the preparation of carbon bisulphide: it is present
in blast furnace gas, is generated in mines (especially in deep seams
containing pyrites), arises in tar distillation, from use of gas lime
in tanning, and in the preparation and use of sodium sulphide: large
quantities of the gas are generated in the putrefactive processes
connected with organic sulphur-containing matter such as glue making,
bone stores, storage of green hides, in the decomposition of waste water
in sugar manufacture and brewing, in the retting of flax, and especially
in sewers and middens.
Both _acute_ and _chronic_ poisoning are described.
The following case is reported by the Union of Chemical Industry in 1907:
Three plumbers who were employed on the night shift in a chemical factory
and had gone to sleep in a workroom were found in a dying condition two
hours later. In the factory barium sulphide solution in a series of large
saturating vessels was being converted into barium carbonate by forcing
in carbonic acid gas; the sulphuretted hydrogen gas evolved was collected
in a gasometer, burnt, and utilised for manufacture of sulphuric acid. In
the saturating vessels were test cocks, the smell from which enabled the
workers to know whether all the sulphuretted hydrogen gas had been driven
out. If this was so the contents of the retort were driven by means of
carbonic acid gas into a subsidiary vessel, and the vessel again filled
with barium sulphide liquor. From these intermediate vessels the baryta
was pumped into filter presses, the last remains of sulphuretted hydrogen
gas being carried away by a fan into a ventilating shaft. The subsidiary
vessel and ventilating shaft were situated in front of the windows of
the repairing shop. On the night in question a worker had thoughtlessly
driven the contents out of one saturating vessel before the sulphuretted
hydrogen gas had been completely removed, and the driving belt of the fan
was broken. Consequently, the sulphuretted hydrogen gas escaping from
the subsidiary vessel entered through the windows of the workshop and
collected over the floor where the victims of the unusual combination of
circumstances slept.
In another chemical works two workers suffered from severe poisoning
in the barium chloride department. The plant consisted of a closed vat
which, in addition to the openings for admitting the barium sulphide
liquor and sulphuric acid, had a duct with steam injector connected
with the chimney for taking away the sulphuretted hydrogen gas. Owing
to a breakdown the plant was at a standstill, as a result of which the
ventilating duct became blocked by ice. When the plant was set in motion
again the sulphuretted hydrogen gas escaped through the sulphuric acid
opening. One of the workers affected remained for two days unconscious.[1]
The report of the Union of Chemical Industry for 1905 cites a case
where an agitating vessel, in which, by action of acid on caustic
liquor, sulphuretted hydrogen gas was given off and drawn away by a fan,
had to be stopped to repair one of the paddles. The flow of acid and
liquor was stopped, and the cover half removed. The deposit which had
been precipitated had to be got rid of next in order to liberate the
agitator. The upper portion of the vessel was washed out with water,
and since no further evolution of sulphuretted hydrogen was possible
from any manufacturing process, the work of removing the deposit was
proceeded with. After several bucketfuls had been emptied the man inside
became unconscious and died. The casualty was no doubt due to small
nests of free caustic and acid which the spading brought into contact
and subsequent developement of sulphuretted hydrogen afresh. A case
is reported of sulphuretted hydrogen poisoning in a man attending to
the drains in a factory tanning leather by a quick process. Here, when
sulphurous acid acts on sodium sulphide, sulphuretted hydrogen is given
off. In cleaning out a trap close to the discharge outlet of a tannery
two persons were rendered unconscious, and the presence of sulphuretted
hydrogen was shown by the blackening of the white lead paint on a house
opposite and by the odour.[2]
In the preparation of ammonium salts Eulenberg[3] cites several cases
where the workers fell as though struck down, although the processes were
carried on in the open air. They quickly recovered when removed from the
spot.
Oliver cites the case where, in excavating soil for a dock, four men
succumbed in six weeks; the water contained 12 vols. per cent. of
sulphuretted hydrogen.
Not unfrequently acute poisoning symptoms result to sewer men. Probably
sulphuretted hydrogen gas is not wholly responsible for them, nor for
the chronic symptoms complained of by such workers (inflammation of the
conjunctiva, bronchial catarrh, pallor, depression).
In the distillation processes connected with the paraffin industry
fatalities have been reported.
CARBON BISULPHIDE
MANUFACTURE.—Carbon bisulphide is prepared by passing sulphur vapour over
pure coal brought to a red heat in cast-iron retorts into which pieces of
sulphur are introduced. The crude carbon bisulphide requires purification
from sulphur, sulphuretted hydrogen, and volatile organic sulphur
compounds by washing with lime water and subsequent distillation.
Use is made of it principally in the extraction of fat and oil from bones
and oleaginous seeds (cocoanut, olives, &c.), for vulcanising, and as a
solvent of rubber. It is used also to extract sulphur from gas purifying
material and for the preparation of various chemical substances (ammonium
sulphocyanide, &c.), as well as for the destruction of pests (phylloxera
and rats).
Fat and oil are extracted from seeds, bones, &c., by carbon bisulphide,
benzine, or ether, and, to avoid evaporation, the vessels are as airtight
as possible and arranged, as a rule, for continuous working.
_Vulcanisation_ is the rendering of rubber permanently elastic by its
combination with sulphur. It is effected by means of chloride of sulphur,
sulphide of barium, calcium, or antimony, and other sulphur-containing
compounds, heat and pressure, or by a cold method consisting in the
dipping of the formed objects in a mixture of carbon bisulphide and
chloride of sulphur. The process of manufacture is briefly as follows:
The raw material is first softened and washed by hot water and kneading
in rolls. The washed and dried rubber is then mixed on callender
rolls with various ingredients, such as zinc white, chalk, white
lead, litharge, cinnabar, graphite, rubber substitutes (prepared by
boiling vegetable oils, to which sulphur has been added, with chloride
of sulphur). In vulcanising by aid of heat the necessary sulphur or
sulphur compound is added. Vulcanisation with sulphur alone is only
possible with aid of steam and mechanical pressure in various kinds of
apparatus according to the nature of the article produced. In the cold
vulcanisation process the previously shaped articles are dipped for a few
seconds or minutes in the mixture of carbon bisulphide and chloride of
sulphur and subsequently dried in warm air as quickly as possible.
In view of the poisonous nature of carbon bisulphide, benzine is much
used now. In the cold method use of chloride of sulphur in benzine can
replace it altogether.
Instead of benzine other solvents are available—chlorine substitution
products of methane (dichlormethane, carbon tetrachloride). In other
processes _rubber solvents_ are largely used, for instance, acetone, oil
of turpentine, petroleum benzine, ether, and benzene. Rubber solutions
are used for waterproofing cloth and other materials.
Similar to the preparation and use of rubber is that of guttapercha. But
vulcanisation is easier by the lead and zinc thiosulphate process than by
the methods used in the case of rubber.
EFFECTS ON HEALTH OF CS₂ AND OTHER DANGERS TO HEALTH IN THE RUBBER
INDUSTRY.—In the manufacture of carbon bisulphide little or no danger is
run either to health or from fire.
In the rubber trade the poisonous nature of _benzine_ and _chloride of
sulphur_ have to be borne in mind, and also the considerable risk of
_lead poisoning_ in mixing. Cases of plumbism, especially in earlier
years, are referred to.[1]
_Benzine_ poisoning plays only a secondary part in the rubber industry.
No severe cases are recorded, only slight cases following an inhalation
of fumes.
Cases of poisoning are recorded in a motor tyre factory in Upsala.[2]
Nine women were affected, of whom four died. Whether these cases were due
to benzene or petroleum benzine is not stated. It is remarkable that two
such very different substances as benzene and benzine should be so easily
confused.
But that in the rubber industry cases of benzene poisoning do actually
occur is proved by the following recent cases: Rubber dissolved in benzol
was being laid on a spreading machine in the usual way. Of three men
employed one was rendered unconscious and died.[3]
In a rubber recovery process a worker was rendered unconscious after
entering a benzol still, also two others who sought to rescue him. Only
one was saved.
Cases of aniline poisoning are reported where aniline is used for
extracting rubber.[4]
_Chloride of sulphur_, by reason of its properties and the readiness
with which it decomposes (see Chloride of Sulphur), causes annoyance to
rubber workers, but rarely poisoning.
Much importance attaches to _chronic carbon bisulphide poisoning_ in the
rubber industry. Many scientists have experimented as to its poisonous
nature (see especially on this Part II, p. 194).
Lehmann’s[5] experiments show that a proportion of 0·50-0·7 mg. of CS₂
per litre of air causes hardly any symptoms; 1·0-1·2 mg. slight effects
which become more marked on continued exposure; 1·5 mg. produces severe
symptoms. About 1·0 mg. per litre of air is the amount which may set up
chronic effects. In vulcanising rooms this limit may easily be exceeded
unless special preventive measures are adopted.
Laudenheimer[6] has made several analyses of the proportion of CS₂ in
workrooms. Thus 0·9-1·8 mg. per litre of air were found in a room where
pouches were vulcanised; 0·5-2·4 mg. were aspirated one-half metre
distant from the dipping vessels; and 0·18-0·27 mg. in the room for
making ‘baby comforters.’
In analyses made some years ago proportions of 2·9-5·6 mg. were obtained.
Although literature contains many references to CS₂ poisoning, too
much importance ought not to be attached to them now in view of the
arrangements in modern well-equipped vulcanising premises. Laudenheimer
has collected particulars of 31 cases of brain, and 19 of nervous,
diseases among 219 persons coming into contact with CS₂ between 1874
and 1908, all of whom had been medically attended. In the last ten
years, however, the psychical symptoms were seven times less than in the
preceding period. Between 1896 and 1898 the average proportion of brain
disease in the vulcanising department was 1·95 per cent., and of nervous
diseases 0·22 per cent., as compared with 0·92 per cent. and 0·03 per
cent. in the textile. Moreover, he maintains that practically all workers
who come at all into contact with CS₂ must be to some extent affected
injuriously by it.
Studies on the injurious nature of CS₂ date from the years 1851-60, when
the French writers Pazen, Duchenne, Beaugrand, Piorry, &c., came across
cases from the Parkes’ process (cold vulcanisation by means of CS₂ and
SCl₂). Delpech[7] published in 1860 and 1863 details of twenty-four
severe cases in rubber workers, some of which were fatal, and at the
same time described the pitiable conditions under which the work was
carried on.
In Germany Hermann, Hirt and Lewin, and Eulenberg dealt with the subject,
but their work is more theoretical in character; and in Laudenheimer’s
work referred to the histories of several cases are given in detail.
Mention should be made of the injury caused to the skin by the fluids
used in extraction of fat and in vulcanising—especially by benzine
and carbon bisulphide. Perrin considers the effect due partly to the
withdrawal of heat and partly to the solvent action on the natural
grease, producing an unpleasant feeling of dryness and contraction of the
skin.
ILLUMINATING GAS
Illuminating gas is obtained by the dry distillation of coal. The
products of distillation are subjected on the gasworks to several
purifying processes, such as condensation in coolers, moist and dry
purifying, from which valuable bye-products (such as tar, ammonia,
cyanogen compounds) are obtained. The purified gas is stored in gas
holders containing on an average 49 per cent. hydrogen, 34 per cent.
methane, 8 per cent. carbonic oxide, 1 per cent. carbon dioxide, 4
per cent. nitrogen, and about 4 per cent. of the heavy hydrocarbons
(ethylene, benzene vapour, acetylene, and their homologues) to which the
illuminating properties are almost exclusively due.
The most important stages in its preparation will be shortly described.
_Distillation_ is effected in cylindrical, usually horizontal, fireclay
retorts placed in a group or setting (fig. 11), which formerly were
heated by coke but in modern works always by gas. Charging with coal and
removal of the coke takes place about every four hours, often by means of
mechanical contrivances.
Iron pipes conduct the products of distillation to the _hydraulic main_.
This is a long covered channel extending the entire length of the stack
and receiving the gas and distillate from each retort. In it the greater
part of the tar and of the ammoniacal water condense and collect under
the water which is kept in the main to act as a seal to the ends of the
dip pipes, to prevent the gas from passing back into the retort when
the latter is opened. While the liquid flows from the hydraulic main
into cisterns, the gas passes into _coolers_ or _condensers_, tall iron
cylinders, in which, as the result of air and water cooling, further
portions of the tar and ammoniacal liquor are condensed. To free it still
more from particles of tar the gas passes through the _tar separator_.
[Illustration: FIG. 11.—Manufacture of Illuminating Gas. Horizontal
fireclay retorts placed in a setting and heated by gas(_after Ost_)]
The tar which remains behind flows through a tube to the cistern. From
the tar separator the gas goes through _scrubbers_ (fig. 12), where the
gas is washed free of ammonia and part of the sulphuretted hydrogen and
carbon dioxide with water. The scrubbers are tower-like vessels filled
with coke or charcoal through which the gas passes from below upwards,
encountering a spray of water. Several scrubbers in series are used, so
that the water constantly becomes richer in ammonia. Mechanical scrubbers
are much used, so-called standard washers; they are rotating, horizontal
cylinders having several chambers filled with staves of wood half dipping
in water. In them the same principle of making the gas meet an opposing
stream of water is employed, so that the last traces of ammonia are
removed from the gas.
The various purifying apparatus through which the gas has to pass cause
considerable resistance to its flow. Escape in various ways would occur
had the gas to overcome it by its own pressure, and too long contact of
the gas with the hot walls of the retorts would be detrimental. Hence an
exhauster is applied to the system which keeps the pressure to the right
proportion in the retorts and drives on the gas.
[Illustration: FIG. 12.—Washer or Scrubber]
After purification in the scrubbers _dry purification_ follows, having
for its object especially removal of compounds of sulphur and cyanogen
and carbon dioxide. To effect this several shallow receptacles are
used, each having a false bottom upon which the purifying material is
spread out. The boxes are so arranged that the gas first passes through
purifying material which is almost saturated and finally through fresh
material, so that the material becomes richer in sulphur and cyanogen
compounds. The _gas purifying material_ formerly used was slaked lime,
and it is still frequently used, but more generally bog iron ore or
artificially prepared mixtures are used consisting mostly of oxide of
iron. The saturated purifying material is regenerated by oxidation on
spreading it out in the air and turning it frequently. After having been
thus treated some ten times the mass contains 50 per cent. sulphur, and
13 to 14 per cent. ferrocyanide.
[Illustration: FIG. 13.—Manufacture of Illuminating Gas. Diagrammatic
view (_after Lueger_) A Retort setting and hydraulic main; B Condensers
and coolers; C Exhauster; D Well; E Water tank; F Tar extractor;
G Scrubber; H Purifier; I Station meter; K Gas holder; L Pressure
regulator.]
The _naphthalene_ in illuminating gas does not separate in the condenser,
and therefore is generally treated in special apparatus by washing the
gas with heavy coal tar.
The gas purified, as has been described, is measured by a meter and
stored in gasometers. These are bells made up of sheet iron which hang
down into walled receptacles filled with water to act as a water seal,
and are raised by the pressure of the gas which streams into them. The
gas passes to the network of mains by pressure of the weight of the
gasometer, after having passed through a pressure regulating apparatus.
As to recovery of bye-products in the illuminating gas industry, see the
sections on Ammonia, Cyanogen Compounds, Tar, Benzene, &c.
EFFECT ON HEALTH.—Opinions differ as to the effect on health which
employment in gas works exerts. This is true of old as well as of modern
literature.
Hirt[1] maintains that gas workers suffer no increase in illness because
of their employment. They reach, he says, a relatively high age and their
mortality he puts down at from 0·5 to 1 per cent. (my own observations
make me conclude that the average mortality among persons insured in sick
societies in Bohemia is 1 per cent., so that Hirt’s figure is not high).
Layet[2] agreed with Hirt, but was of opinion that gas workers suffered
from anæmia and gastro-intestinal symptoms attributable to inhalation of
injurious gases. The sudden symptoms of intoxication, ‘exhaustion and
sinking suddenly into a comatose condition,’ which he attributes to the
effect of hydrocarbons and sulphuretted hydrogen gas, may well have been
the symptoms of carbonic oxide poisoning.
Goldschmidt[3] in recent literature considers manufacture of illuminating
gas by no means dangerous or unhealthy, and speaks of no specific
maladies as having been observed by him. Nevertheless, he admits with
Layet that the men employed in the condensing and purifying processes are
constantly in an atmosphere contaminated by gas, and that the cleaning
and regeneration of the purifying mass is associated with inflammation of
the eyes, violent catarrh, and inflammation of the respiratory passages,
since, on contact of the purifying mass with the air, hydrocyanic acid
gas, sulphocyanic acid gas, and fumes containing carbolic, butyric, and
valerianic acids are generated.
Other writers[4] refer to the injurious effects from manipulating the
purifying material. In general, though, they accept the view, without
however producing any figures, that work in gas works is unattended with
serious injury to health and that poisonings, especially from carbonic
oxide, are rare. Such cases are described,[5] but the authors are not
quite at one as to the healthiness or otherwise of the industry. The one
opinion is based on study of the sick club reports for several years of
a large gas works employing some 2400 workers (probably Vienna).[6] The
average frequency of sickness (sickness percentage), excluding accidents,
was 48·7 per cent. The conclusion is drawn that the health conditions
of gas workers is favourable. It is pointed out, however, that diseases
of the respiratory and digestive organs (12·8 and 10·16 per cent. of
the persons employed) are relatively high, and that the mortality (1·56
per cent.) of gas-workers is higher than that of other workers. This
is attributed to the constant inhalation of air charged with injurious
gases. Work at the retorts, coke quenching, and attending to the
purifying plant are considered especially unhealthy.
The other figures relate to the Magdeburg gas works; they are higher
than those quoted. The morbidity of the gas workers was found to be 68·5
per cent., of which 18 per cent. was due to disease of the digestive
system, 20·5 per cent. to disease of the respiratory organs, and 1 per
cent. to poisoning. No details of the cases of poisoning are given.
Carbonic oxide poisoning is said to be not infrequent, the injurious
effect of cleaning the purifiers is referred to, and poisoning by
inhalation of ammonia is reported as possible.
Still, no very unfavourable opinion is drawn as to the nature of the
work. The sickness frequency in sick clubs is about 50 per cent., and
even in well-managed chemical works Leymann has shown it to be from 65 to
80 per cent. The recently published elaborate statistics of sickness and
mortality of the Leipzig local sickness clubs[7] contain the following
figures for gas workers: Among 3028 gas workers there were on an
average yearly 2046 cases of sickness, twenty deaths, and four cases of
poisoning. The total morbidity, therefore, was 67·57 per cent., mortality
0·66 per cent., and the morbidity from poisoning 0·13 per cent. Diseases
of the respiratory tract equalled 10·63 per cent., of the digestive
tract 10·87 per cent., of the muscular system 13·10 per cent., and from
rheumatism 11·10 per cent. These figures, therefore, are not abnormally
high and the poisoning is very low.
Still, industrial cases of poisoning in gas works are recorded. Of these
the most important will be mentioned. Six persons were employed in a
sub-station in introducing a new sliding shutter into a gas main, with
the object of deviating the gas for the filling of balloons. A regulating
valve broke, and the gas escaped from a pipe 40 cm. in diameter. Five
of the men were rendered unconscious, and resuscitation by means of
oxygen inhalation failed in one case. In repairing the damage done two
other cases occurred.[8] In emptying a purifier a worker was killed from
failure to shut off the valve.
Besides poisoning from illuminating gas, industrial poisoning in gas
works is described attributable, in part at least, to ammonia. Thus the
report of the factory inspectors of Prussia for 1904 narrates how a
worker became unconscious while superintending the ammonia water well,
fell in, and was drowned.
A further case is described in the report of the Union of Chemical
Industry for 1904. In the department for concentrating the gas liquor
the foreman and an assistant on the night shift were getting rid of the
residues from a washer by means of hot water. The cover had been removed,
but, contrary to instructions, the steam had not been shut off. Ammonia
fumes rushed out and rendered both unconscious, in which condition there
were found by the workmen coming in the morning.[9]
In the preparation of ammonium sulphate, probably in consequence of
too much steam pressure, gas liquor was driven into the sulphuric acid
receiver instead of ammonia gas. The receiver overflowed, and ammonia gas
escaped in such quantity as to render unconscious the foreman and two men
who went to his assistance.[10]
The use of illuminating gas in industrial premises can give rise to
poisoning. Thus the women employed in a scent factory, where so-called
quick gas heaters were used, suffered from general gas poisoning.[11]
In Great Britain in 1907 sixteen cases of carbonic oxide poisoning from
use of gas in industrial premises were reported.
COKE OVENS
Coke is obtained partly as a residue in the retorts after the production
of illuminating gas. Such _gas coke_ is unsuitable for metallurgical
purposes, as in the blast furnace. Far larger quantities of coal are
subjected to dry distillation for metallurgical purposes in coke ovens
than in gas works. Hence their erection close to blast furnaces. In the
older form of coke oven the bye-products were lost. Those generally used
now consist of closed chambers heated from the outside, and they can be
divided into coke ovens which do, and those which do not, recover the
bye-products. These are the same as those which have been considered
under manufacture of illuminating-gas—tar, ammonia, benzene and its
homologues, cyanogen, &c. In the coke ovens in which the bye-products are
not recovered the gases and tarry vapours escaping on coking pass into
the heating flues, where, brought into contact with the air blast, they
burn and help to heat the oven, while what is unused goes to the main
chimney stack.
[Illustration: FIG. 14.—Distillation Coke Oven (_after Lueger_)
A, A´ Coal to be coked; B, B´ Standpipes; C Hydraulic main; D Condensing
apparatus; E Purified gas: F, F´ Air inlets; G G,´ G´´ Combustion
chambers.]
In the modern _distillation ovens_ with recovery of the bye-products the
gases escaping from the coal are led (air being cut off as completely as
possible) through ascending pipes into the main collector, where they are
cooled, and the tarry ingredients as well as a part of the ammonia are
absorbed by water; subsequently the gases pass through washing apparatus
with a view to as complete a recovery of the ammonia and benzene as
possible. The purified gases are now again led to the ovens and burnt
with access of air in the combustion chambers between two ovens.
Generally these ovens are so constructed as to act as non-recovery ovens
also (especially in starting the process).
The coal is charged into the ovens through charge holes on the top
and brought to a level in the chambers either by hand or mechanically.
Removal of the coke block after completion of the coking operation is
done by a shield attached to a rack and pinion jack. Afterwards the coke
is quenched with water.
Recovery of the _bye-products_ of coke distillation ovens is similar to
the method described for illuminating gas, i.e. first by condensation
with aid of air or water cooling, then direct washing with water
(generally in scrubbers), whereby tar and ammonia water are recovered.
_Recovery of benzene_ and its homologues (see Benzene later) depends on
the fact that the coke oven gases freed from tar and ammonia are brought
into the closest possible contact with the so-called wash oils, i.e. coal
tar oils with high boiling-point (250-300° C.). For this purpose several
washing towers are employed. The waste oil enriched with benzene is
recovered in stills intermittently or continuously and used again.
EFFECTS ON HEALTH.—Injury to health from work at coke ovens is similar
to that in the manufacture of illuminating gas. There is the possibility
of carbonic oxide poisoning from escape of gas from leakage in the
apparatus. As further possible sources of danger ammonia, cyanogen and
sulpho-cyanogen compounds, and benzene have to be borne in mind.
In the distillation of the wash oil severe poisoning can arise, as in a
case described, where two men were fatally poisoned in distilling tar
with wash oil.[1]
The details of the case are not without interest. The poisoning occurred
in the lavatory. The gases had escaped from the drain through the
ventilating shaft next to the closet. The gases came from distillation of
the mixture of tar and wash oil, and were driven by means of air pumps
in such a way that normally the uncondensed gases made their way to the
chimney stack. On the day of the accident the pumps were out of use, and
the gases were driven by steam injectors into the drain. Analysis showed
the gases to contain much sulphuretted hydrogen. When this was absorbed,
a gas which could be condensed was obtained containing carbon bisulphide
and hydrocarbons of unknown composition (? benzene). Only traces of
cyanogen and sulpho-cyanogen compounds were present. Physiological
experiment showed that poisoning was attributable mainly to sulphuretted
hydrogen gas, but that after this was removed by absorption a further
poisonous gas remained.
Other Kinds of Power and Illuminating Gas
_Producer gas_ or _generator gas_.—Manufacture of producer gas consists
in dealing separately with the generation of the gas and the combustion
of the gases which arise. This is effected by admitting only so much air
(primary air supply) to the fuel as is necessary to cause the gases to
come off, and then admitting further air (secondary supply) at the point
where the combustion is to take place; this secondary supply and the gas
formed in the gas producer are heated in regenerators before combustion
by bringing the gases to be burnt into contact with _Siemens’s heaters_,
of which there are four. Two of these are always heated and serve to heat
the producer gas and secondary air supply.
[Illustration: FIG. 15.—Horizontal Regenerative Grate (_after Lueger_)]
A producer gas furnace, therefore, consists of a gas producer, a gas main
leading to the furnace hearth, the heater, and the chimney.
[Illustration: FIG. 16.—Step Regenerative Grate (_after Lueger_)]
The gas producer is a combustion chamber filled with coal in which
the coal in the upper layer is burnt. Generators may have horizontal
or sloping grate (see figs. 15 and 16). The _Siemens’s_ heaters or
regenerators are chambers built of, and filled loosely with, fireclay
bricks and arranged in couples. Should the gas producers become too hot,
instead of the chambers subdivided air heaters are used, whereby the hot
furnace gases are brought into contact with a system of thin-walled,
gastight fireclay pipes, to which they give up their heat, while the
secondary air supply for the furnace is led beside these pipes and so
becomes heated indirectly. Previous heating of the producer gas is here
not necessary; no valves are needed because the three streams of gas all
pass in the same direction.
[Illustration: FIG. 17A.—Siemens’s Regenerative Furnace
L Air; G Gas
FIG. 17B.—Siemens’s Regenerative Furnace]
Such air heating arrangements are used for heating the retorts in gas
works, for melting the ‘metal’ in glass works, and very generally in
other industries, as they offer many technical and hygienic advantages.
Generator gas from coke contains 34 per cent. carbonic oxide, 0·1 per
cent. hydrogen, 1·9 per cent. carbon dioxide, and 64 per cent. nitrogen.
_Blast furnace gas._—Blast furnace gas is formed under the same
conditions as have been described for generator gas; it contains more
carbon dioxide (about 10 per cent.). (Further details are given in the
section on Iron—Blast Furnaces.)
_Water gas._—Water gas is made by the passage of steam through
incandescent coal, according to the equation:
C + H₂O = CO + 2H.
The iron gas producer, lined with firebrick, is filled with anthracite
or coke and heated by blowing hot air through it. This causes producer
gas to escape, after which steam is blown through, causing water gas to
escape—containing hydrogen and carbonic oxide to the extent of 45-50 per
cent., carbon dioxide and nitrogen 2-6 per cent., and a little methane.
The blowing of hot air and steam is done alternately, and both kinds of
gas are led away and collected separately, the water gas being previously
purified in scrubbers, condensers, and purifiers. It serves for the
production of high temperatures (in smelting of metals). Further, when
carburetted and also when carefully purified in an uncarburetted state,
it serves as an illuminant. The producer gas generated at the same time
is used for heating purposes (generally for heating boilers).
_Dowson gas._—Dowson gas is obtained by collecting and storing together
the gases produced in the manner described for water gas. Under the
grating of the wrought-iron gas producer (lined with firebrick and
similarly filled with coke or anthracite) a mixture of air and steam,
produced in a special small boiler, is blown through by means of a
Körting’s injector.
Before storage the gas is subjected to a purifying process similar to
that in the case of water gas. The mixed gas consists of 1 vol. water gas
and 2-3 vols. producer gas, with about 10-15 vols. per cent. H, 22-27
vols. per cent. CO, 3-6 per cent. CO₂, and 50-55 per cent. N. It is an
admirable power gas for driving gas motors (fig. 18).
_Mond gas_ similarly is a mixed gas obtained by blowing much superheated
steam into coal at low temperature. Ammonia is produced at the same time.
[Illustration: FIG. 18.—Power Gas Installation (_after Lueger_)
A Steam boiler
a Steam injector
B Furnace
b Charging hopper
c Cover g
d Valve C
e Cock D
f Vent pipe
g Steam Pipe
C Washer
D Coke tower
E Sawdust purifier]
_Suction gas._—In contradistinction to the Dowson system, in which air
mixed with steam is forced into the producer by a steam injector, in the
suction gas plant the air and steam are drawn into the generator by the
apparatus itself. The whole apparatus while in action is under slight
negative pressure. A special steam boiler is unnecessary because the
necessary steam is got up in a water container surrounding or connected
with the cover of the generator. The plant is set in motion by setting
the fire in action by a fan.
[Illustration: FIG. 19.—Suction Gas Plant (_after Meyer_)]
Fig. 19 shows a suction gas plant. B is the fan. Above the generator
A and at the lower part of the feed hopper is an annular vessel for
generating steam, over the surface of which air is drawn across from
the pipe e, passing then through the pipe f into the ash box g, and
then through the incandescent fuel. The gas produced is purified in the
scrubber D, and passes then through a pipe to the purifier containing
sawdust and to the motor.
_Carburetted gas._—Gas intended for illuminating purposes is carburetted
to increase its illuminating power, i.e. enriched with heavy
hydrocarbons. Carburetting is effected either by a hot method—adding the
gases distilled from mineral or other oils—or by a cold method—allowing
the gas to come into contact with cold benzol or benzine. Coal gas as
well as water gas is subjected to the carburetting process, but it
has not the same importance now in relation to illuminating power, as
reliance is more and more being placed on the use of mantles.
ACETYLENE
_Calcium carbide._—Acetylene is prepared from calcium carbide, which on
contact with water gives off acetylene.
_Calcium carbide_ is prepared electro-chemically. A mixture of burnt lime
and coke is ground and melted up together at very high temperature in an
electric furnace, in doing which there is considerable disengagement of
carbonic oxide according to the equation:
CaO + 3C = CaC₂ + CO.
The furnaces used in the production of calcium carbide are of different
construction. Generally the furnace is of the nature of an electric arc,
and is arranged either as a crucible furnace for intermittent work or
like a blast furnace for continuous work.
Besides these there are resistance furnaces in which the heat is created
by the resistance offered to the passage of the current by the molten
calcium carbide.
The carbonic oxide given off in the process causes difficulty. In many
furnaces it is burnt and so utilised for heating purposes. The calcium
carbide produced contains as impurities silicon carbide, ferro-silicon,
calcium sulphide, and calcium phosphide.
_Acetylene_ (C₂H₂), formed by the decomposition of calcium carbide by
means of water (CaC₂ + 2H₂O = Ca(OH)₂ + C₂H₂), furnishes when pure an
illuminating gas of great brilliancy and whiteness. Its production is
relatively easy. Used for the purpose are (1) apparatus in which water
is made to drop on the carbide, (2) apparatus in which the carbide dips
into water and is removed automatically on generation of the gas, (3)
apparatus in which the carbide is completely immersed in water, and (4)
apparatus in which the carbide in tiny lumps is thrown on to water. These
are diagrammatically represented in figs. 20A to 20D.
[Illustration: FIG. 20A.
FIG. 20B.
FIG. 20C.
FIG. 20D.
Acetylene Apparatus—diagrammatic (_after Lueger_) A Dripping; B Dipping;
C Submerging; D Throwing in]
The most important impurities of acetylene are ammonia, sulphuretted
hydrogen gas, and phosphoretted hydrogen. Before use, therefore, it
is subjected to purification in various ways. In Wolf’s method the
gas is passed through a washer (with the object of removing ammonia
and sulphuretted hydrogen gas) and a purifying material consisting
of chloride of lime and bichromate salts. In Frank’s method the gas
passes though a system of vessels containing an acid solution of copper
chloride, and also through a washer. Chloride of lime with sawdust is
used as a purifying agent. Finally, the gas is stored and thence sent to
the consumer (see fig. 21).
[Illustration: FIG. 21.—Acetylene Gas Apparatus (_after Lueger_)]
EFFECTS ON HEALTH.—Almost all the poisoning caused in the industries in
question is due to carbonic oxide gas, of which water gas contains 41 per
cent., generator gas 35 per cent., and suction and Dowson gas 25 per cent.
That industrial carbonic oxide poisoning is not rare the reports of the
certifying surgeons in Great Britain sufficiently show. In the year 1906
fifty-five persons are referred to as having suffered, with fatal issue
in four. In 1907 there were eighty-one, of which ten were fatal. Of the
1906 cases twenty resulted from inhalation of producer, Mond, or suction
gas, sixteen from coal gas (in several instances containing carburetted
water gas), seventeen from blast furnace gas, and one each from charcoal
fumes from a brazier, and from the cleaning out of an oil gas holder.
As causes of the poisoning from suction gas were (1) improper situation
of gas plant in cellar or basement, allowing gas to collect or pass
upward; (2) defective fittings; (3) starting the suction gas plant by the
fan with chimney valve closed; (4) cleaning out ‘scrubbers’ or repairing
valves, &c.; (5) defective gasometer. In the seventeen cases due to blast
furnace gas six were due to conveyance of the gas by the wind from a flue
left open for cleaning purposes into an engineering shed, two to charging
the cupola furnace, two to entering the furnace, and four to cleaning the
flues.
The following are instances taken from recent literature on gas
poisoning[1]: Several cases of poisoning by _water gas_ occurred in a
smelting works. The poisoning originated when a blowing machine driven
by water gas was started. Owing to premature opening of the gas valve
two men employed in a well underneath the machine were overcome. The
attendant who had opened the valve succeeded in lifting both from the
well; but as he was trying to lift a third man who had come to his
assistance and fallen into the well he himself fell in and was overcome.
The same fate befell the engineer and his assistant who came to the
rescue. All efforts to recover the four men by others roped together
failed, as all of them to the number of eight were rendered unconscious.
With the aid of rescue appliances (helmets, &c.) the bodies were
recovered, but efforts at artificial respiration failed.
A workman was killed by _suction gas_ while in the water-closet. It
appeared that some time previously when the plant was installed the
ventilating pipe between the purifier and motor, instead of being led
through the roof, had been led out sideways on a level with the floor
immediately above the closet.
In another case the suction gas attendant had taken out the three-way
cock between the generator and motor for repairs and had not reinserted
it properly, so that when effort was made to start the motor this
failed, as gas only and no air was drawn in. The motor was thought to
be at fault, and the fan was worked so vigorously that the gas forced
its way out through the packing of the flange connections and produced
symptoms of poisoning in the persons employed.
More dangerous than suction gas plants, in which normally no escape
takes place, are installations depending on gas _under pressure_. Such
an installation was used for heating gas irons in a Berlin laundry. The
arrangements were considered excellent. The gas jets were in stoves
from which the fumes were exhausted. The gas was made from charcoal
and contained 13 per cent. of hydrogen. No trace of carbonic oxide was
found in the ironing room on examination of the air. After having been
in use for months the mechanical ventilation got out of order, with the
result that twelve women suffered severely from symptoms of carbonic
oxide poisoning, from which they were brought round by oxygen inhalation.
The laundry reverted to the use of illuminating gas. The conclusion
to be drawn is that installations for gas heating are to be used with
caution.[2]
Industrial poisoning from _blast furnace gas_ is frequent. Two fatal
cases were reported[3] in men employed in the gas washing apparatus. They
met their death at the manhole leading to the waste-water outlet. In
another case a workman entered the gas main three hours after the gas had
been cut off to clear it of the dust which had collected. He succumbed,
showing that such accumulations can retain gas for a long time. Steps had
been taken three hours previously to ventilate the portion of gas main in
question.
A fatal case occurred in the cleaning out of a blast furnace flue which
had been ventilated for 1½ hours by opening all manholes, headplates, &c.
The foreman found the deceased with his face lying in the flue dust; both
he and a helper were temporarily rendered unconscious.
Cases of poisoning by _generator gas_ are described.[4] A workman who had
entered a gasometer containing the gas died in ten minutes, and another
remained unconscious for ten days and for another ten days suffered from
mental disturbance, showing itself in hebetude and weakness of memory.
_Acetylene_ is poisonous to only a slight extent. Impurities in it, such
as carbon bisulphide, carbonic oxide (present to the extent of 1-2 per
cent.), and especially phosphoretted hydrogen gas, must be borne in mind.
American calcium carbide[5] yields acetylene containing 0·04 per cent. of
phosphoretted hydrogen; Lunge and Cederkreutz have found as much as 0·06
per cent. in acetylene.
AMMONIA AND AMMONIUM COMPOUNDS
PREPARATION.—Ammonia and ammonium salts are now exclusively obtained as
a bye-product in the dry distillation of coal, from the ammonia water in
gas works, and as a bye-product from coke ovens.
The ammonia water of gas works contains from 2-3 per cent. of ammonia,
some of which can be recovered on boiling, but some is in a non-volatile
form, and to be recovered the compound must be decomposed. The volatile
compounds are principally ammonium carbonate and, to a less extent,
ammonium sulphide and cyanide; the non-volatile compounds are ammonium
sulphocyanide, ammonium chloride, sulphate, thiosulphate, &c. Other
noteworthy substances in ammonia water are pyridine, pyrrol, phenols,
hydrocarbons, and tarry compounds.
Decomposition of the non-volatile compounds is effected by lime. Hence
the ammonia water is distilled first alone, and then with lime. The
distillate is passed into sulphuric acid, ammonium sulphate being formed.
Distillation apparatus constructed on the principle usual in rectifying
spirit is used, so that continuous action is secured; the ammonia water
flows into the apparatus continuously and is freed of the volatile
compounds by the steam. At a later stage milk of lime is added, which
liberates the ammonia from the nonvolatile compounds.
Of the ammonium salts there require mention:
_Ammonium sulphate_ ((NH₄)₂SO₄), which serves for the production of other
ammonium salts. It is usually centrifugalised out from the sulphuric acid
tank previously described.
_Ammonium chloride_ (sal-ammoniac, NH₄Cl) is formed by bringing the
ammonia fumes given off in the process described in contact with
hydrochloric acid vapour. The crude salt so obtained is recrystallised or
sublimed.
_Ammonium phosphate_ ((NH₄)₂HPO₄) is made in an analogous manner by
leading ammonia into phosphoric acid. It is useful as an artificial
manure.
_Ammonium carbonate_ is made either by bringing together ammonia vapour
and carbonic acid or by subliming ammonium sulphate with calcium
carbonate. It is very volatile. The thick vapour is collected and
purified in leaden chambers.
[Illustration: FIG. 22.—Preparation of Ammonia. Column Apparatus of
Feldman (_after Ost_)
A, B, C Columns; D Saturator; (a) Settling tank and regulator for flow of
ammonia; (b) Economiser; (f) Milk of lime; (g) Pump]
_Caustic ammonia_ is prepared either from gas liquor or, more usually,
from ammonium sulphate by distillation with caustic alkali in a
continuous apparatus.
USE OF AMMONIA.—Ammonia is used in laundries and bleaching works in
dyeing and wool washing. It is used especially in making ammonium salts,
in the preparation of soda by the Solvay process (see Soda Manufacture),
and in making ice artificially.
It is used also in the preparation of indigo, in lacquers and colours,
and the extraction of chloride of silver, &c.
EFFECTS ON HEALTH.—Industrial ammonia poisoning is rare. It occurs
most frequently in gas works and occasionally in its use, especially
the manufacture of ammonium salts. Those engaged in subliming ammonium
carbonate incur special risk, but often it is not the ammonia vapour so
much as the escaping evil-smelling gases containing carbon bisulphide and
cyanogen compounds which are the source of trouble.
Occasionally in the production of ice through leakage or by the breaking
of carboys of ammonia accidental poisoning has occurred.
Some cases are cited from recent literature:
A worker was rendered unconscious and drowned in an ammonia water
well.[1] Two workers were poisoned (one fatally) in the concentration of
gas liquor. Three workers were gassed (one fatally) in the preparation
of ammonium sulphate in a gas works. Probably as the result of excessive
steam pressure gas water was driven over with the ammonia into the
sulphuric acid vessel.[2]
Eulenberg[3] reports the occurrence of sulphuretted hydrogen gas
poisoning in the production of ammonium salts. The workers succumbed as
though shot, although work was being carried on in the open air. They
recovered when removed from the poisonous atmosphere.
In a large room of a chemical factory phosphoric acid was being saturated
with ammonia gas water in an iron lead-lined vessel. Carbonic acid gas
and hydrogen gas were evolved, but not to such extent as to be noticeable
in the large room. A worker not employed in the room had to do something
close to the vessel, and inhaled some of the fumes given off. A few
yards from the vessel he was found lying unconscious, and although
removed into the open air failed to respond to the efforts at artificial
respiration.[4]
Lewin, in an opinion delivered to the Imperial Insurance Office,
describes poisoning in a man who during two days had been employed
repairing two ammonia retorts in a chemical factory. On the evening of
the second day he suffered from severe symptoms of catarrh, from which
he died five days later. Lewin considered the case to be one of acute
ammonia poisoning.[5]
Ammonia is frequently used in _fulling_ cloth, the fumes of which collect
on the surface after addition of sulphuric acid to the settling vats.
This is especially liable to occur on a Monday, owing to the standing
of the factory over the Sunday, so that entrance into the vats without
suitable precautions is strictly forbidden. Despite this, a worker did
go in to fetch out something that had fallen in, becoming immediately
unconscious. A rescuer succumbed also and lost his life. The first worker
recovered, but was for long incapacitated by paralytic symptoms.
Cases of poisoning in _ice factories_ and refrigerator rooms from
defective apparatus are reported.
Acute and chronic poisoning among sewer men are due mainly to
sulphuretted hydrogen gas and only partly to ammonia. The more ammonia
and the less sulphuretted hydrogen sewer gases contain the less poisonous
are they.
CYANOGEN COMPOUNDS
TREATMENT OF THE MATERIALS USED IN GAS PURIFYING.—Cyanogen compounds
are still sometimes prepared by the original method of heating to
redness nitrogenous animal refuse (blood, leather, horn, hair, &c.) with
potash and iron filings; potassium cyanide is formed from the nitrogen,
carbon, and alkali, and this with the sulphur and iron present is easily
converted into potassium ferrocyanide (yellow prussiate of potash,
K₄FeC₆N₆) by lixiviation of the molten mass. It crystallises out on
evaporation.
Cyanogen compounds are obtained in large quantity from the material
used in purifying the gas in gas works. This saturated spent material
contains, in addition to 30-40 per cent. of sulphur, 8-15 per cent. of
cyanogen compounds and 1-4 per cent. of sulphocyanogen compounds.
By lixiviation with water the soluble ammonium salts are extracted from
the purifying material. This solution furnishes _sulphocyanide of
ammonium_, from which the remaining unimportant sulphocyanide compounds
are obtained (used in cloth printing). The further treatment of the
purifying material for potassium ferrocyanide is rendered difficult
because of the sulphur, which is either removed by carbon bisulphide
and the ferrocyanide obtained by treatment with quicklime and potassium
chloride, or the mass is mixed with quicklime, steamed in closed vessels,
lixiviated with water, and decomposed by potassium chloride; ferrocyanide
of potassium and calcium separates out in crystals, and this, treated
with potash, yields potassium ferrocyanide.
The well-known non-poisonous pigment Prussian blue is obtained by
decomposing ferrocyanide of potash with chloride or oxide of iron in
solution.
_Potassium cyanide_ (KCN) is prepared from potassium ferrocyanide by
heating in absence of air, but it is difficult to separate it entirely
from the mixture of iron and carbon which remains. All the cyanogen is
more easily obtained in the form of potassium and sodium cyanide from
potassium ferrocyanide by melting it with potash and adding metallic
sodium.
The very poisonous _hydrocyanic acid_ (prussic acid, HCN) is formed by
the action of acids on potassium or sodium cyanide; small quantities
indeed come off on mere exposure of these substances to the air. The
increasing demand for potassium cyanide has led to experimental processes
for producing it synthetically.
One method consists in the production of potassium cyanide from potash
and carbon in a current of ammonia gas. Small pieces of charcoal are
freed from air, saturated with a solution of potash, dried in the absence
of air, and heated in upright iron cylinders to 100° C., while a stream
of ammonia gas is passed through.
Again, sodium cyanide is prepared from ammonia, sodium, and carbon by
introducing a definite amount of sodium and coal dust into melted sodium
cyanide and passing ammonia through. The solution is then concentrated in
vacuo and sodium cyanide crystallises out on cooling.
USE OF CYANIDES.—Potassium cyanide is principally used in the recovery
of gold, in gold and silver electroplating, in photography, for
soldering (it reduces oxides and makes metallic surfaces clean), for
the production of other cyanogen compounds, for the removal of silver
nitrate stains, &c. Hydrocyanic acid gas is given off in electroplating,
photography, in smelting fumes, in tanning (removing hair by gas lime),
&c.
EFFECTS ON HEALTH.—Industrial cyanogen poisoning is rare. Weyl[1] states
that he could find no case in any of the German factory inspectors’
reports for the twenty years prior to 1897, nor in some twenty-five
volumes of foreign factory inspectors’ reports. I have found practically
the same in my search through the modern literature.
Of the very few references to the subject I quote the most important.
A case of (presumably) chronic hydrocyanic acid poisoning is described in
a worker engaged for thirteen years in silver electroplating of copper
plates.[2] The plates were dipped in a silver cyanide solution and then
brushed. After two years he began to show signs of vomiting, nausea,
palpitation, and fatigue, which progressed and led to his death.
A case of sudden death is described[3] occurring to a worker in a sodium
cyanide factory who inhaled air mixed with hydrocyanic acid gas from a
leaky pipe situated in a cellar. The factory made sodium cyanide and
ammonium sulphate from the residue after removal of the sugar from
molasses. This is the only definite case of acute cyanogen poisoning in a
factory known to me. I believe that under modern conditions, in which the
whole process is carried on under negative pressure, chance of escape of
cyanogen gases is practically excluded.
It should be mentioned that hydrocyanic acid vapour is given off in the
burning of celluloid. In this way eight persons were killed at a fire in
a celluloid factory.[4]
Skin affections are said to be caused by contact with fluids containing
cyanogen compounds, especially in electroplating. It is stated that
workers coming into contact with solutions containing cyanides may
absorb amounts sufficient to cause symptoms, especially if the skin
has abrasions. Such cases are described.[5] In electroplating, further,
in consequence of the strong soda solutions used, deep ulceration and
fissures of the skin of the hand can be caused.
COAL TAR AND TAR PRODUCTS
Of the products of the illuminating gas industry tar has considerably the
most importance. Coal tar as such has varied use in industry, but far
greater use is made of the products obtained by fractional distillation
from it such as benzene, toluene, naphthalene, anthracene, carbolic acid,
pyridine, and the other constituents of tar, a number of which form the
starting-point in the production of the enormous coal-tar dye industry.
Especially increasing is the consumption of benzene. In Germany alone
this has increased in ten years from 20 to 70 million kilos. This is
partly due to the need of finding some cheap substitute for benzine, the
consumption and cost of which has increased, and it has in many respects
been found in benzene.
Besides benzene and its homologues, toluene, anthracene, and naphthalene
are valuable. Anthracene is used in the manufacture of alizarine and
naphthalene in that of artificial indigo and of the azo-colours. Carbolic
acid (phenol) and the homologous cresols serve not only as disinfectants
but also in the manufacture of numerous colours and in the preparation
of picric acid and salicylic acid. Further, a number of pharmaceutical
preparations and saccharin are made from the constituents of tar.
The important _constituents of tar_ are:
1. Hydrocarbons of the methane series: paraffins, olefines; hydrocarbons
of the aromatic series: benzene and its homologues, naphthalene,
anthracene, phenanthrene, &c.
2. Phenols (cresols, naphthols).
3. Sulphides: sulphuretted hydrogen, carbon bisulphide, mercaptan,
thiophene.
4. Nitrogen compounds: ammonia, methylamine, aniline, pyridine, &c.
5. Fifty to sixty per cent. of tar consists of pitch constituting a
mixture of many different substances which cannot be distilled without
decomposition.
_Crude tar_, i.e. tar which separates in the dry distillation of coal,
is employed as such for preserving all kinds of building materials,
for tarring streets, as plastic cement, as a disinfectant, in the
preparation of roofing paper or felt, lampblack, briquettes, &c.
_Brattice cloth_ and _roofing felt_ are made by passing the materials
through hot tar and incorporating sand with them; in doing this heavy
fumes are given off.
_Lampblack_ is made by the imperfect combustion of tar or tar oil by
letting them drop on to heated iron plates with as limited an air supply
as possible; the burnt gases laden with carbon particles are drawn
through several chambers or sacks in which the soot collects.
[Illustration: FIG. 23.—Tar Still (_after Krämer_)]
_Briquettes_ (patent fuel) are made by mixing small coal (coal dust) with
tar or pitch and then pressing them in moulds.
The separation and recovery of the valuable ingredients is effected by
_fractional distillation_. This is carried out by heating the tar at
gradually increasing temperature in a wrought-iron still, the bottom
of which is arched and having a cast-iron still head, or in horizontal
boilers by direct fire. Before commencing the distillation the tar is
freed as far as possible of water by storage. On gradual increase of
temperature the volatile constituents, the so-called ‘light oil,’ and
later the heavier volatile constituents come over. The constituents are
liberated in a gaseous state and are collected in fractions. The pitch
remains behind in the still. Considerable quantities of coal tar are not
distilled for pitch. Often the light oils and a portion of the heavy oils
are collected, when soft pitch remains, or, if the light oils and only
a very small portion of the heavy oils are collected, _asphalt_ remains
behind, this residue being used as a basis for the manufacture of roofing
felt. The vapours are condensed in iron coils round which cold water
circulates. The receivers in which the distillate is caught are changed
at definite times as the temperature gradually rises. If five fractions
have come over they are called (1) first runnings, (2) light oil to 170°
C., (3) middle oil (carbolic oil to 230° C.), (4) heavy oil to 270° C.,
and lastly (5) anthracene oil, which distills at over 270° C.; the pitch
remaining behind is let out of the still by an opening at the bottom.
We will briefly sketch the further treatment and use of these fractions,
so far as a knowledge of the most important processes is necessary for
our purpose.
1. The _light oils_ (including first runnings) coming over up to 170° C.
are again distilled and then purified with sulphuric acid in lead-lined
cast-iron or lead-lined wooden tanks. The dark-coloured acid used for
purifying after dilution with water, which precipitates tarry matters,
is treated for ammonium sulphate; the basic constituents of the light
oils extracted with sulphuric acid and again liberated by lime yield
_pyridine_ (C₅H₅N) and the homologous pyridine bases, a mixture of which
is used for denaturing spirit. After the light oils have been washed
with dilute caustic soda liquor, whereby the phenols are removed, they
are separated by another fractional distillation into (_a_) crude benzol
(70°-130° C.) and (_b_) solvent naphtha (boiling-point 130°-170° C.).
_Crude benzol_ (70°-140° C.) consists chiefly of benzene and toluene
and is separated into its several constituents in special rectifying
apparatus. For this production of pure benzene (boiling-point 80°-82° C.)
and pure toluene (boiling-point 110° C.) fractionating apparatus is used
(fig. 24).
The _commercial products_ in use which are obtained from the fractional
distillation of the light oil are:
(_a_) _Ninety per cent. benzol_, so called because in the distillation 90
per cent, should come over at a temperature of 100° C. It is made up of
80-85 per cent. benzene, 13-15 per cent. toluene, 2-3 per cent. xylene,
and contains, as impurities, traces of olefines, paraffins, sulphuretted
hydrogen, and other bodies.
(_b_) _Fifty per cent. benzol_ contains 50 per cent. of constituents
distilling at 100° C. and 90 per cent. at 120° C.; it is a very mixed
product, with only 40-50 per cent. of benzene.
(_c_) _Solvent naphtha_, so called because it is largely used for
dissolving rubber, is free from benzene, but contains xylene and its
homologues and other unknown hydrocarbons.
[Illustration: FIG. 24.—Column Apparatus of Hickman for Distillation of
Benzene (_after Ost_)
A Still body; B Analysing column; C Cooler; D Condenser for pure
distillate.]
Benzol is widely used. Ninety per cent. benzol is largely used in
the chemical industry, serving for the preparation of dye stuffs,
pharmaceutical preparations, scents, &c. In other industries it took the
place of benzine and also of turpentine oil, especially in the paint
industry, since it evaporates quickly and readily dissolves resins.
Hence it is used in the preparation of quick drying ship’s paints, as a
protection against rust, and as an isolating lacquer (acid proof colours)
for electrical apparatus, in the production of deck varnishes, and as a
solvent of resins.
This use of benzol in the paint industry is by no means unattended with
danger, as benzol is poisonous. Far less harmful, if not altogether
without risk, is use of benzol free solvent naphtha—but this evaporates
only slowly and hence cannot take the place of benzol.
Benzol serves further for fat extraction from bones in manure factories
and of caffein from coffee beans.
Again, it is used as a motive power in motor vehicles.
The solvent naphtha above mentioned with boiling-point above 140° C. and
all the light oils are employed in chemical cleaning and for dissolving
indiarubber (see Indiarubber).
These are known in the trade erroneously as ‘benzine,’ which
unfortunately often leads to confusion with petroleum benzine (see
Petroleum) and to mistakes in toxicological accounts of poisoning.
2. Between 150° and 200° C. the _middle oil_ comes over, from which on
cooling _naphthalene_ (C₁₀H₈) crystallises out, and is subsequently
washed with caustic soda liquor and with acid; it is re-distilled and
hot pressed. The remaining liquor yields, when extracted with caustic
soda, _phenol_ (carbolic acid, C₆H₅OH), which, on addition of sulphuric
acid or carbonic acid, separates from the solution and then—generally in
special factories—is obtained pure by distillation and special purifying
processes.
From the sodium salt of carbolic acid (sodium phenolate) _salicylic
acid_ (C₆H₄OH.COOH) is obtained by combination with compressed CO₂ at a
temperature of 150° C. _Picric acid_ (trinitrophenol, C₆H₂OH.(NO₂)₃) is
obtained by treating phenol with a mixture of sulphuric and nitric acids
(nitration). The yellow crystals of this explosive which separate are
carefully washed, recrystallised, centrifugalised, and dried.
3. The _heavy oils_ which come over between 200° and 300° C. containing
cresols, naphthols, naphthaline, quinoline bases, fluid paraffins, &c.,
are seldom separated further. The disinfectants lysol, sapocarbolic, &c.,
are obtained from such fractions.
The heavy oils are much in use for _impregnating wood_ (piles, railway
sleepers, &c.), to prevent rotting. This is done in special creosoting
installations. The wood is first freed from moisture under vacuum and
lastly the heavy oil forced in. This is a better means of preserving
timber than the analogous method by means of chloride of zinc.
4. _Anthracene oil_ or ‘green oil’ comes over between 300° and 400° C.
and contains the valuable anthracene which crystallises out, is separated
from the oil in filter presses, or dried in centrifugal machines.
_Alizarin_ dyes are made from it. Raw anthracene oil further is used
commercially as a paint under the name of carbolineum for preserving wood.
5. The _pitch_ remaining behind in the still serves (like tar) for
making varnishes, patent fuel, &c. For our purpose use of pitch in
the preparation of iron varnishes which adhere to metals and protect
them from oxidation have interest. Pitch and the heavy oils are melted
together or, if for thin varnishes, dissolved in solvent naphtha. The
volatile constituents evaporate after the coat has been applied.
EFFECTS ON HEALTH.—Severe injury to health or poisoning cases scarcely
arise through manipulations with or use of tar. Inhalation, however, of
large quantities of tar vapour is without doubt unpleasant, as a number
of poisonous substances are contained in the fumes. And the ammonia water
which separates on standing can give off unpleasantly smelling odours
from the sulphur compounds in it, especially if it comes into contact
with waste acids, with consequent development of sulphuretted hydrogen
gas.
I could not find in the literature of the subject references to any
clearly proved case of poisoning from tar emanations. But deserving of
mention in this connection are the _effects on the skin_ caused by tar.
Workers coming into contact with tar suffer from an inflammatory
affection of the skin, so-called tar eczema, which occasionally takes
on a cancerous (epithelioma) nature similar to chimney-sweep’s cancer,
having its seat predominantly on the scrotum. In lampblack workers who
tread down the soot in receptacles the malady has been observed to affect
the lower extremities and especially the toes.
In tar distillation and in the _production_ and _use_ of _benzene_
industrial poisoning frequently occurs. Many cases are recorded, but in
several the immediate exciting cause is doubtful, and consequently it is
often difficult to classify the cases.
Most frequently the manufacture and use of benzene come in question.
Besides this, in tar distillation poisoning may be caused by other
substances, such as sulphuretted hydrogen gas, carbonic oxide gas, &c. In
the production of antipyrin, aspirin, &c., and in the preparation and use
of anthracene injury to health is recognised.
From the list of recognised cases of these forms of poisoning the most
characteristic are chosen from the recent literature on the subject.
The Prussian factory inspectors’ reports for 1904 describe the following:
In cleaning out a tar still two workers were killed by inhalation of gas.
The nature of the gas was not ascertained. But what probably happened was
that the cock on the foul gas pipe collecting the gases from the stills
leaked and allowed fumes to pass over from one still to another.
A foreman and worker were rendered unconscious on entering a receiver
for heavy oil for cleaning purposes. On treatment with oxygen gas they
speedily recovered.
_Industrial benzene poisoning_ is especially frequent now in view of the
increasing use to which it is put. Several cases have proved fatal.
A worker, for instance, forgot to open the cock for the water to cool the
condenser, so that some of the benzene vapour remained uncondensed. The
case proved fatal.
The Report of the Union of Chemical Industry for 1905 stated that a
worker on night duty, whose duty it was to regulate the introduction
of steam and the cooling of the benzol plant, was found lying dead in
front of the building. Inquiry showed that he had not opened the valve
for running the distillate into the appropriate receiver. Eight thousand
litres overflowed.
In an indiarubber extracting factory a worker was rendered unconscious
while inspecting a benzol still; before entering he had omitted to
observe the instructions to drive steam through and have a mate on watch
at the manhole. Two other workmen were similarly affected who went to the
rescue without adoption of precautions. Only one survived.
In a further accident (already mentioned under ‘Coke Furnaces’) two
workmen were killed. In the factory in question the thick tar from the
coke ovens was being distilled under slight pressure. The air pumps,
however, were out of order, and temporary use was being made of Körting’s
injectors, whereby the steam and tar constituents were cooled and led
into the drain in front of the closet, near to which was a ventilating
shaft. Probably, in addition to benzene and its homologues, sulphuretted
hydrogen and cyanogen compounds were present in the poisonous gases.
In cleaning out a benzene extracting apparatus a workman was killed by
the stagnant fumes in it.
A similar case of benzene poisoning occurred in a naphthalamine works
through inspecting an extracting vessel which had contained benzene
and naphthalamine and had to be cleaned. The vessel had been empty for
twenty-two hours and had been washed and ventilated, but through a
leaking pipe benzene had dropped down into it. The workman engaged was
rendered unconscious inside the retort, but was rescued by an engineer
equipped with a breathing helmet. Others who without such apparatus tried
to effect a rescue were overcome, and one who had entered the retort
succumbed.[1]
Benzene poisoning has often occurred in the cleaning of tanks, &c., for
the transport and storage of the substance. The following examples are
taken from the Reports of the Union of Chemical Industry.
A worker during the pause for breakfast had, unknown to his employer,
cleaned out an empty truck for crude benzol. Later he was with difficulty
removed unconscious through the manhole and could not be resuscitated.
Only a short time previously a similar occurrence had taken place in the
same factory.
Two further fatal cases were reported in 1908 in the cleaning out of
railway tank waggons. The tank had previously been thoroughly sprayed
with water. The partition plates which are required in such tanks
increase the difficulty of cleaning from the manhole. After the foreman
had tested the air by putting his head inside and considered it free from
danger, a man entered to clean out the deposit; another man on watch
outside had evidently gone in for rescue purposes. Resuscitation in both
cases failed.
A worker died and several were affected in the cleaning out of a benzol
storage tank in a tar distillery. The tank had had air blown through it
several weeks before, and had been thoroughly cleaned by steam and water.
Also in the inspection the greatest care was taken in only permitting
work for short spells. This shows that, notwithstanding great care, the
last traces of benzol cannot be entirely removed and that quite small
quantities are sufficient to cause severe and even fatal poisoning.
Workers should only clean out tanks, therefore, when properly equipped
with helmets.
In the German factory inspectors’ reports for 1902 a case of intoxication
is described in a man who was engaged painting the inside of an iron
reservoir with an asphalt paint dissolved in benzol.
Of special interest is a fatal case from inhalation of benzol fumes in
a rubber factory. Rubber dissolved in benzol was being rubbed into the
cloth on a spreading machine in the usual way. The cloth then passes
under the cleaning doctor along the long heated plate to the end rolls.
Of the three men employed at the process one was found to be unconscious
and could not be brought round again.
The cases described[2] of poisoning with impure benzol in a pneumatic
tyre factory in Upsala are, perhaps, analogous. Here nine young women had
severe symptoms, four of whom died.
In reference to the cases which occurred in rubber factories it is
conceivable that carbon bisulphide played a part, since in such factories
not only are mixtures of benzol and carbon bisulphide used, but also
frequently the ‘first runnings’ of benzol, which, on account of the high
proportion (sometimes 50 per cent.) of carbon bisulphide in them, make an
excellent solvent for rubber.
From some coke ovens crude benzol was collected in two large iron
receivers. They were sunk in a pit projecting very little above the
ground. To control the valves the workmen had to mount on the receiver,
the manholes of which were kept open during filling. The pit was roofed
over and two wooden shafts served both for ventilation and as approaches
to the valves. One summer day benzol had been blown in the usual way
into a railway truck and a worker had entered the space to control the
valves. Some time afterwards he was found in a doubled-up position on
the receiver, grasping the valves, from which later he fell off down to
the bottom of the pit. Three rescuers entered, but had to retire as they
became affected. A fourth worker, in the presence of the manager, was let
down by a rope, but succumbed immediately and was dragged up a corpse.
Finally, equipped with a smoke helmet, a rescuer brought up the lifeless
body of the first man. It was believed that the benzol had distilled
over warm and had evaporated to such an extent as to fill with fumes the
unsuitably arranged and inadequately ventilated space. Possibly other
volatile compounds were responsible for the poisoning.[3]
A similar though less serious accident occurred to a foreman who forgot
to set the cooling apparatus at work at the commencement of distillation,
and became unconscious from the escaping fumes, as also did a rescuer.
The latter was brought round by oxygen inhalation, but the former,
although alive when recovered, succumbed despite efforts at artificial
respiration.
A fatal case occurred in an aniline factory where benzol fumes had
escaped owing to faulty arrangement of the valves. The worker, although
ordered at once to leave the room, was found there ten minutes later dead.
Interesting are the following cases of accidents due to use of paints
containing benzol.
In painting a retort with an anti-corrosive paint called ‘Original
Anti-corrosive,’ unconsciousness followed on completion of the painting,
but by prompt rescue and medical assistance life was saved. The accident
was attributed to benzol fumes from the paint insufficiently diluted by
the air coming in at the open manhole. A similar case arose from use
of a rust-preventing paint—‘Preolith’—and only with difficulty was the
man using it pulled out from the inside of the steam boiler. Although
resuscitated by oxygen inhalation, he was incapacitated for eight days.
Crude benzol was a constituent of ‘Preolith.’ Obviously use of such
paints in closely confined spaces is very risky.
The frequency of such poisonings caused Schaefer,[4] Inspector of
Factories in Hamburg, to go fully into the question. He lays stress on
the dangerous nature of paints containing a high proportion of benzol,
but considers use of unpurified constituents with boiling-point between
130°-170° C., such as solvent naphtha, as free from risk (cf. in Part II
the experiments on benzene and the commercial kinds of benzol). Schaefer
mentions that in 1903 and 1904 cases of unconsciousness from painting
the inside of boilers were numerous. The proportion of benzol in the
paints was 20-30 per cent. In 1905 and 1906 the cases were attributable
rather to inhalation of hydrocarbons in cleaning of apparatus. Use of
‘Dermatin’ affected two painters. One case in 1906 happened to a man
painting the double bottom of a ship in Hamburg harbour with ‘Black
Varnish Oil’ through the manhole, in doing which he inhaled much of the
fumes. This paint consisted of coal-tar pitch in light coal-tar oil, the
latter constituent (distilling at 170° C.) amounting to 31-33 per cent.
Investigation showed further that the bulk of the tar oil volatilised at
ordinary temperatures and so quickly dried. Sulphuretted hydrogen gas was
given off on slight warming. The person after using it for some time felt
poorly, and then became ill with severe inflammation of the respiratory
passages, which proved fatal after twenty-four days.
Several similar cases occurred in 1908 and 1909. Painting the inside
of a boiler with ‘Auxulin’ caused unconsciousness in four persons,
of whom three were rescuers. A fatal case was due to use of a patent
colour containing 30-40 per cent. benzol in an entirely closed-in space
(chain-well), although the worker was allowed out into fresh air at
frequent intervals.
A case of chronic industrial xylene poisoning is described in a worker
using it for impregnating indiarubber goods. The symptoms were nervous,
resembling neurasthenia.