The Tri-Nitro-Glycerin Manufactured at the Hoosac
Tunnel—How Tri-Nitro-Glycerin is Made—How
Stored—How Gutta-Percha is Purified—How the
Conducting Wires are Insulated—How the Exploders
are Manufactured.
There are probably few of my readers who have ventured to trust
themselves within a Nitro-Glycerin manufactory; the very name is
sufficient to make the passer-by quicken his step, till he is a safe
distance beyond the dreaded precinct. Some account of such a factory
will, accordingly, be interesting to many who are familiar with the
article, perhaps have used it, but whose curiosity has not been of such
a nature as to induce them to pay a visit to the works, where the least
negligence involves a death penalty.
About 100 yards beyond the West shaft of the Hoosac Tunnel, is to be
seen a board fence surrounding about ten acres of ground, with the
announcement, “NITRO-GLYCERIN WORKS;—DANGEROUS;—NO VISITORS ADMITTED.”
A drive leading between two rows of buildings brings the “visitor” to
the acid house, a well-ventilated building, 150 feet long. Here are
11 stills, each seven feet long and two feet in diameter. Under these
a light, slow fire burns, which is carefully attended to, for the
temperature must be kept moderate. In each of these stills is placed
300 lbs. of nitrate of soda and 375 lbs. of sulphuric acid. A stoneware
pipe conducts the gases, at a temperature of about 180°F, from each
still into a stone receiver or condenser, or rather a series of four
condensers connected by stoneware pipes, ranged on a platform three
feet above the ground. Into the first of these 150 lbs. of sulphuric
acid is poured, into the second 150 lbs., into the third 100 lbs., and
the fourth is empty. The nitrous vapor passes from the still to the
first condenser, where a portion of it, forming as it condenses nitric
acid, is taken up by the sulphuric acid; the remainder passes on to
the second, third and fourth condensers, though a very small portion
is left to pass into the last, which only requires to be emptied once
a month. It takes about twenty-four hours for the still to complete
the conversion of its contents into nitric acid, at the end of which
time the resultant mixture of acids, about 600 lbs., is run off into
carboys, twelve of these being filled from three stills. About 100
carboys are generally kept in stock, as the acid does not spoil when
kept closed. These carboys are then emptied into a soapstone tank
having a capacity of 18 carboys, and an iron pipe, connected with the
main leading from two blowers in the engine house, is inserted into
the acid, causing a current of air to agitate it so as to remove the
nitrous fumes, mix it thoroughly and bring it all to uniform strength.
Formerly, this was effected by removing the acid into a glass vessel
containing about forty gallons, and it required boiling for hours;
the mode now practised occupies only five minutes and the risk of
fracture of a glass vessel in a sand bath is avoided. The acid is then
carried into the converting room, about one hundred feet long and well
lighted, where it is weighed, seventeen pounds being poured into each
of one hundred and sixteen stone pitchers which are arranged in nine
wooden troughs placed in the centre and at the end of the room, and
these troughs are now filled with ice-cold water, or ice and salt, so
as to rise within four inches of the top of the jar. On shelves above
the troughs, are arranged glass jars, one to each stone pitcher. Into
each of these glass jars, two pounds, by weight, of pure Glycerin is
poured, and this, by means of a siphon, with a rubber tube attached,
about two feet long, falls drop by drop into the corresponding pitcher
of mixed sulphuric and nitric acids. Immediately below the shelf, in
which the Glycerin jar stands, is a 2¼ inch iron pipe, which brings a
current of cold air from the receivers connected with the two blowers
before-mentioned. This current of air is distributed to each jar,
while the acid and glycerin are mixing, by a rubber pipe, to which is
attached a glass tube 16 inches long, and with a ¼ inch bore. During
the hour and a half to two hours that the glycerin takes to run off
into the pitchers, the greatest care, and the closest attention is
requisite. The three men whose duty it is to attend to the mixing
process, have each a row of pitchers to watch, walking the whole
time up and down, beside them, with thermometer in hand, and as the
nitrous fumes rise from the forming Nitro-Glycerin, they stir the
mixture, with the glass tube before-mentioned, in any pitcher that
may be giving out too violent fumes. Sometimes this is caused by the
glycerin running a little freely, which fires the mixture, wastes the
glycerin, forming oxalic acid, and developes unpleasant vapors. In
such a case, by pushing back a little wooden peg in the glass jar, the
flow of glycerin is lessened, and by stirring with the glass tube the
nitrous vapors dispelled. Should the engine also stop working by any
unforseen circumstance, the current of air will of course be stopped,
when the mixture will take fire. In this case, it is necessary to
stir the mixture, and at once stop the flow of glycerin. When the
glycerin and acid is all mixed, and the nitrous fumes cease to appear,
the Nitro-Glycerin from each pitcher is dumped into a large tank of
water, at a temperature of 70°, about 450 lbs. of Nitro-Glycerin being
the amount of each batch manufactured. The Nitro-Glycerin sinks
to the bottom and is covered by about six feet of water. Here it
remains for fifteen minutes to be subsequently washed free from any
impurities. This tank goes through the floor into a basement chamber,
its bottom being on a slight incline, so that the Nitro-Glycerin may
run out easily. The water is first drawn off from the top of the
Nitro-Glycerin, and then the latter is run into a wooden swinging tub,
in shape somewhat like an old-fashioned butter churn, but a good deal
larger in diameter. In this it is washed five times, three times with
plain water, and twice with soda, a current of air working through it
at the same time. The water from this tub is run off into a wooden
trough, which conveys it to a barrel buried in the earth, in the side
of which a hole carries it to another barrel a little lower down the
hill, and this again to another barrel, whence it finds its way to the
dump of rocks being removed from the tunnel, any Nitro-Glycerin that
may have escaped in the washing process being collected and retained in
one or other of these barrels.
The Nitro-Glycerin is by this time thoroughly washed and ready to
store in the magazine, 300 feet distant, to which it is carried in a
couple of copper pails at a time, by a man with a yoke, similar to
what milkmen use for carrying their pails. Curious thought, that a
man carrying a couple of harmless looking pails with only a little
colorless fluid in them, should have enough explosive matter about him
to annihilate a regiment.
In the magazine the Nitro-Glycerin is poured into “crocks,” as they are
called, earthenware jars holding 60 lbs. These crocks are then placed
in a wooden tank 2½ feet deep, which holds 20 of them, and immersed
to within six inches from the top of the jars in water warmed by a
small pipe from the boiler, to raise the temperature to 70°, at which
temperature it is kept all the time, as nearly as possible. They remain
in this water for about 72 hours, during which time any impurities
still remaining rise to the surface as scum, and are skimmed off with
a spoon. The Nitro-Glycerin is then chemically pure, transparent as
water, refracts light powerfully, and is ready for packing. The tin
cans, lined with paraffine and containing 56 lbs. each, are placed
in a shallow wooden trough, and the Nitro-Glycerin being poured from
the crocks into copper cans, is again poured into the tins through a
gutta-percha funnel, the bottom of the trough being covered with a
thick layer of plaster of paris, which absorbs and renders harmless any
drops of Nitro-Glycerin that may be spilt. The tins when filled are
then placed in a wooden trough containing iced water, or ice and salt,
where the Nitro-Glycerin is slowly crystallized or congealed; in this
condition, it is stored away in small magazines 300 feet distant, in
amounts of 30 to 40 cans each, until required for use.
[Illustration]
When the Nitro-Glycerin is to be conveyed over the mountains, the tins
are packed in open wooden boxes, with two inches of sponge at the
bottom, and four rubber tubes underneath; these are long enough to
allow the ends to come one inch over the top of the tin on opposite
sides, thus interposing two elastic tubes between the outside of the
tin and the inside of the wooden box, rendering it perfectly safe to
carry. Each tin is cellular, i. e., from the top of each tin to the
bottom a tube passes, about ten inches deep and 1½ inch in diameter,
for the purpose of thawing the congealed Nitro-Glycerin when the
blaster is ready to use it, liquefaction being effected with water
of 70° to 90°. The tins being closed with a cork wrapped in bladder,
are put into a sleigh or wagon, covered in summer with a layer of ice
and blankets, and may thus be carried any distance in this purified
crystalline state, as safely as so many tubs of butter.
The reflecting reader will note the care taken to purify the
Nitro-Glycerin; it occupies 1½ hours to make it, about 72 hours to
purify, and about 48 hours to congeal or crystallize it. And yet there
are parties who attempt to make and vend Nitro-Glycerin, and induce
miners and contractors to use it, taken direct from the precipitating
tank, with all its impurities tending to decomposition, and requiring
only time and moderate temperature for spontaneous explosion; hence, I
believe many accidents.
Proceeding back to the factory, two ice-houses will be noticed,
capable of containing 400 tons of ice, required for crystallizing
Nitro-Glycerin in summer. There is a small engine-house with a boiler
of fifteen horse power, and engine of about ten horse power; this
latter, to pump water into the washing tank, run the two “blowers,” and
give power in the gutta-percha factory. The air is not pumped directly
into the pipe which distributes it to the pitchers, as the pressure
would not be always uniform; but into two receivers under the floor of
the factory, whence it is evenly distributed, and deprived of watery
vapor, which if blown into the pitchers would raise the temperature and
vitiate the product.
Attached to the factory is a building about 90 feet long, for covering
the copper wire (used in exploding) with gutta-percha, so as to render
the insulation perfect. The first process is to purify the crude
gutta-percha which is imported in blocks about a foot long. This is
placed against a rasping machine with toothed knives about four inches
apart, which crush and tear the gutta-percha to pieces, delivering it
into a trough of water. The impurities sink, while the gutta-percha
floats. It is then warmed in a steam jacketed kettle, and when still
plastic is put into another tearing or rasping machine with another
series of knives set closer together, from this it drops into a trough
of clean water, more dirt separating. This is repeated two or three
times, as it is most important that no extraneous matter should be
retained in the gutta-percha, because it would interfere with perfect
insulation, and so place in jeopardy the lives of several men. It is
again steamed and put into a “masticator” consisting of a fluted roller
working in a steam jacket; here it is “chawed up” for about six hours,
until it arrives at a proper consistence; it is then passed between
two smooth cylinders heated by steam, and transferred thence into a
cylinder, where it is pressed through gauze wire, under a pressure of
four tons to the inch. Being thoroughly cleansed, it is then steamed,
masticated and pressed between the cylinders, and is ready to cover
the copper wire. Five wires at a time, horizontally parallel to one
another, are passed through a gun metal mould with a disc at the
further end perforated with five holes but little larger than the wires
themselves, placed at the base of an upright cylinder. The gutta-percha
is inserted in the top of this cylinder, and a pressure of 95 tons is
put upon it by means of a screw, when it is pressed into slots in the
mould surrounding the wires, which are then drawn from the holes in
the disc, through a trough of water 80 feet long, and back again: it
is then wound on drums ready for use. The “leading” wire receives two
coatings, separate discs having larger bores being attached to the
brass cylinder.
A house is attached to the factory, for the foreman and his family.
Perfect system pervades this factory, and is absolutely necessary in
the manufacture of Nitro-Glycerin, to ensure safety. The steadiest men
possible are selected for the work, and the foreman of the gutta-percha
department, Mr. Robert Wallace, who has charge of the machinery, is a
skilful machinist and a thoroughly trustworthy Scotchman. He has four
sons employed, of whom one takes charge of the works at Maysville,
Kentucky, another, is foreman of the Nitro-Glycerin factory.
Three men are employed in the acid house, working in three shifts
of eight hours each, but they do not actually work more than seven
hours; every movement is like clock work, every man has his place and
special duty, which he is expected to perform at the proper time. In
the morning, at 7 or 7½ A. M., two men dump the carboys of acid into
the soapstone tank and mix them, while a third is filling the glass
jars with glycerin. This operation takes about an hour. One draws the
acid, another weighs it, and a third carries it to the troughs. After
an interval during which the acids cool, three men attend closely to
the converting of glycerin into Tri-Nitro-Glycerin, knowing that their
safety, and the safety of every man on the works, depends on themselves
alone, during this process. After the Nitro-Glycerin is dumped into
the water tank, two men are employed in washing it, down stairs, while
two wash the stone pitchers with water; more water, temperature about
60°, is swilled on the floors so as to keep them scrupulously clean and
perfectly free from atoms of Nitro-Glycerin, which, stepped upon while
the men are at work, might send them to eternity, and the building to
smithereens. The room is then prepared for next day’s operations, and
by about one or two o’clock, after six, or at most seven hours’ work,
the day’s task is done. Mr. Wilson, in charge of the purifying process,
canning, and preparing for shipment, has now been over four years at
this work.
Making exploders is a distinct operation, requiring great precision.
The materials of which the priming for fuses is composed, are prepared
in my private laboratory, and consist of sulphide and phosphide of
copper with chlorate of potash. Considerable nicety of manipulation
is required to prepare the former of these compounds so as to obtain
homogeneous, uniform sulphides and phosphides, and, from the failure of
several chemists—and some of our best have attempted the manufacture—to
prepare them, I attach great importance to this work, invariably
making them myself. For, if prepared with the above ingredients, no
accident can occur from atmospheric electricity, friction etc., a
contingency which all other primings now in use are liable to. The
priming is then taken to the warehouse where from three to four hands
are employed in making it up into exploders. Two insulated wires from
4 to 12 feet long, are inserted in the smallest end of a wooden tube,
previously dipped in boiled paraffine, ¾ inch long and ⅛ inch diameter
at one end, and 3/16 at the other, to which they are fastened by a
shoulder of gutta-percha. Immediately before the priming is inserted,
an electric spark is passed through and between the wires where the
priming is put so as to ascertain that the insulation is perfect, and
to guard against the possibility of a miss-fire. This being proved,
the priming is put in at the other end of the tube, and a small paper
plug boiled in paraffine inserted; then a copper cap, ¾ inch long and
⅜ inch diameter, receives 20 grains of fulminate of mercury, on the
top of which a varnish is poured which prevents any of the fulminate
from being shaken out by accident, or affected by vibration. This
copper cap is then placed in a larger wooden cap 1½ inch long, the fuse
inserted about ¼ inch, when it fits tight, the wooden part painted with
asphaltum varnish around the joints, and the exploder is complete and
ready for service. Three hands employed ought to make 1,000 a day of
these exploders.
Having thus given a full account of the manufacture of Nitro-Glycerin
and its appurtenances, I will conclude with the remark that there is
no danger in the manufacture when due precaution is used; but, to
paraphrase the language of Professor Tyndall, in his preface to “Hours
of Exercise in the Alps”: “For rashness, ignorance, or carelessness,
Nitro-Glycerin leaves no margin; and to rashness, ignorance, or
carelessness, three-fourths of the catastrophes which shock us are to
be traced.”
[Illustration]