CHAPTER V.
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 safedistance 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 fractureof 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 theamount 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.
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 wateryvapor, 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 7½a. 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, invariablymaking 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.”