The mining and metallurgical laboratory, is a place in which mechanical and chemical working-tests are made on ores, fuels and furnace materials. It is of quite recent origin. The first laboratory of this kind to be used in connection with teaching was put into operation at the Massachusetts Institute of Technology. The laboratory was given from the first into the charge of Prof. R. H. Richards, who, by improving its methods and enlarging its scope, has brought it to the position which it occupies to-day as the leading representative of its class. Private laboratories for making tests upon ores had previously existed here and there, especially on the Pacific coast, for silver and gold ores; but in the educational field the Massachusetts Institute of Technology was the pioneer. Today there is hardly a school of mines in this country that has not a more or less complete mining and metallurgical laboratory & equipment. In European mining-schools there is very little laboratory-teaching. Most of them are located in mining-districts, where the students can personally see and engage in the practical work of mining, concentrating and smelting. Those which are in large cities, at a distance from mines, labor under a great disadvantage. The student only sees practical work when he makes an occasional visit to mining regions, and is otherwise left entirely to theory. It must not be inferred, however, that the location of a school in a mining district can make the laboratory superfluous. On the contrary, one who, like the present writer, has received his training in such a school, sees clearly afterwards how one-sided becomes the teaching in a mining district without the addition of such laboratory-work. The instructor is only too liable to give most, if not all, of his time to elaborating unnecessary details of the local methods, past as well as present, and to pass over with amazing celerity those branches of the subject not represented in his district. Yet even as regards local work, upon which he puts such undue stress, he is likely to be too theoretical, because, not being practically engaged in it, or able to apply such tests as are furnished in the laboratory, he necessarily falls into too abstract a way of viewing the whole subject. The result is that his instruction tends to produce theorists, who speak with unwarranted assurance concerning the most difficult problems which the engineer has to solve; but who, if confronted with a simple, concrete question, are at a loss what to do.

That this lack of laboratory training in German technical schools (which are among the foremost in Europe) is beginning to be realized as a defect was evidenced by the intense interest and careful study bestowed upon the subject by the commissioners who came to the Columbian Exposition two years ago. They did not hesitate to praise our system and to express the hope that it might be adapted to meet their necessities on the other side of the Atlantic.

The mining and metallurgical laboratory, then, as developed in this country, maybe considered a necessary adjunct to every school of mining engineering. In it the lecture instruction is illustrated with practical experiments, carried out by the students themselves. But it has also a larger scope. By the method of experiment, the student learns how to take hold of each problem as it presents itself and carry it through the different stages until it is, or the reason is discovered why it cannot be, satisfactorily solved. He is thus taught to observe closely, to make careful notes, to compare the results obtained and draw his own inferences and conclusions, and, finally, to report what he has done in a clear and accurate language.

In fitting up a laboratory, we have to consider only the departments of mechanical concentration and metallurgy. Practical mining can be taught only in the mine. Some schools (for instance, the one at Ballarat, Victoria, Australia) are provided with a model of full natural size, showing a shaft with the lode, cross-cuts, etc. While this, apart from the question of expense, is an improvement on the small models formerly so extensively found at schools, it cannot but give a false impression of what a mine really is. The practical study of mining, in this country at least, is carried on today in “ summer schools.” The students spend some time in mines, going systematically through the different kinds of work, and thus becoming sufficiently familiar with mine-operations to listen understandingly to lectures on the subject. It is the merit of Prof. H. S. Munroe, of Columbia College, to have given to the summer school of mining such an impetus that today there is hardly an American mining school without this auxiliary course.

Before discussing in detail the equipment of a laboratory, it is desirable to consider the relation which the laboratory plant should bear, as regards general arrangement and the kind and size of apparatus, to the large-scale working plant of actual practice. A commercial concentrating-works, for example, must treat daily a considerable quantity of ore and must work cheaply, which can only be done if the machines are so connected with one another that the ore shall receive a minimum amount of handling after the work is once underway. In the laboratory, on the other hand, the work, being purely experimental, must be carried on, step by step, in a deliberate and tentative way; and it is, therefore, essential that the operator shall be able to inspect the material under treatment before and after every operation. Consequently, the machines must be separate, that they may be easily accessible for starting, stopping, accelerating, and retarding, and may be connected at will; in short, that the work may be modified indefinitely under the immediate eye of the experimenter. A laboratory in which this principle is neglected carries in it the germ of failure. The writer was once connected with such an establishment, in which a full-sized ore-dressing plant had been erected according to the plan followed in commercial work, viz., the crushed ore was raised by a bucket-elevator to a set of screens placed in a line step-wise, one discharging into the other, and the sized products falling directly upon the jigs and the table below. Of course, a few tons of ore were quickly disposed of; but when the products obtained were examined after the experiment, the observer did not know very much more than he had known before. Such a working plant may be of some value for obtaining more accurate quantitative results after all the necessary details have been determined by the use of detached machines, but it will do little more than substantiate what has already been sufficiently proven.

There are two opposite views concerning the kind and size of machinery proper for laboratory use. One holds that it should follow as closely as possible that of a working plant. The other maintains the superiority of somewhat different and smaller apparatus as better suited to experimental purposes and also more economical. Having tried both kinds, the writer decidedly prefers the latter, especially for educational purposes, and is of the opinion that there are few mechanical questions to which a machine smaller than the commercial size cannot give a satisfactory answer. In addition to the economy, convenience, and other considerations, the saving of physical strain upon the student secured by the smaller apparatus is of importance. Fatiguing operations, especially for those unaccustomed to the work, exhaust the powers and unfit the student for mental effort.

The best size for the single machine can only be arrived at by repeated trials, which have now been made for almost all given cases, as will be shown later on.

In the discussion of the details of a laboratory, it will be more profitable to start from the basis of an actual working laboratory, whatever may be its defects, than from an imaginary perfect one. The laboratories of the Massachusetts Institute of Technology, shown in plan in Fig. 1, may well serve this purpose.

The following are the different rooms, pieces of apparatus, etc., referred to by numbers in Fig. 1. In the present paper numbers enclosed in brackets are to be understood as referring to this figure.

These laboratories are located in the basement of the Rogers building, in the main building of the Institute, and comprise the entire department of mining-engineering and metallurgy, with the exception of the lecture rooms and collections. While at first all the metallurgical work, including dry-assaying, was done in the room marked [48] and the milling-work in the space now covered by machines [13] and [16], there are today a separate furnace-room [48], an assay- and balance-room [37, 44], a milling-room [1] and a blowpipe room [69]. To these may be added two storage rooms [46, 47], a toilet-room [79], a library [73], and the private laboratory [64] and office [77]. Upon closer inspection, it will be seen that the apparatus is pretty closely crowded. Although there is some “ space to grow” [33, 63, 75], and there are places near [1] and [38] still open, there is little room for additional permanent machinery, the available space being necessary for erecting temporary apparatus and giving room to move about in. A laboratory built today with a liberal allowance of space and of funds would probably be planned somewhat differently as regards general arrangement, and would also possess a larger amount and variety of apparatus. The work in it would be easier and could be more conveniently and quickly, but not better, done.

In discussing the machines and furnaces, sufficient data will be given to enable the reader to form a clear idea of the relation which the laboratory apparatus bears to that used in large-scale work.

The apparatus of the laboratory is best classed under three heads, corresponding with its purposes :

A. Concentrating.
B. Sampling and assaying.
C. Metallurgical.

Concentrating Equipment

Coarse Crushing

Coarse-crushing is represented by the Blake Challenge rock-breaker [2], with a receiving-capacity of 4½ by 5 inches, and the Gates rock-breaker [4], with a receiving-hopper 12 inches in diameter. The machines are at a sufficient height above the platform to allow a wheelbarrow or bucket to be placed below the discharge. A pipe, connected with a small suction fan, serves to carry off the dust, if desirable. The Blake is used for crushing lump-ore, the jaws being set 1¼ inches apart; the Gates for smaller sizes, the liners being set at ½ inch. The Dodge and Lowry crushers may be added to the plant if it is desired to crush ore more uniformly than can be done with the Blake or the Gates type; but this will hardly be necessary for the testing of ores, although it might be useful for illustrating class-work. The small Taylor hand-crusher [20] is very convenient for breaking up specimens.

Fine-Crushing

For fine-crushing, there are a pair of Cornish rolls, a stamp battery, a non-discharging ball mill, sets of pans, a sample grinder, and bucking plates.

The Cornish rolls [3], 9 inches in diameter and 9 inches in face, are of chilled iron, without the outside shell so common for large-scale work; are driven by direct- and cross-belt, and make 70 revolutions per minute. The pressure on the sliding- box is maintained by springs. The rolls have a large feed- hopper, with an adjustable discharge slot, holding about 100 pounds of quartzose ore. The crushed ore is directed by three converging pieces of sheet-iron (a short, steep one at the back, and a long, flatter one on each side) towards an oblong opening, 5½ by 27 inches, through which it drops into an oblong sheet-iron box, 14 by 36 inches, of No. 22 iron, with sides 6 inches and ends 4 inches deep. The upper edges of all sheet-iron boxes or vessels used in the laboratory are bent around a ¼-inch iron rod to give them strength and are painted with asphalt- varnish. If the ore is to be screened, an oblong wooden screen- frame, 54 by 11 inches inside dimensions, made of 2½- by 7/8- inch wood, and closed at the upper end, is suspended in a slightly inclined position from four iron (5/16-inch) hooks from the wooden frame of the rolls, and oscillated by an excentric of 1-inch throw and 200 shakes per minute, driven from the main shaft below. The ore drops upon a piece of sheet-iron, 11 by 12 inches, in the upper end of the frame, passing over which it comes to the screen (54 by 12¾ inches). Through this, the finer parts fall into a sheet-iron box, while the coarser ones are carried over into another which adjoins the first. The screens are fastened to the lower sides of their frames by means of angle- hoop-iron and screws.

The crushing capacity of the rolls per hour is 600 pounds of quartzose ore to ¼-inch size, or 300 pounds to 1/8-inch, or 150 pounds to 1/16-inch. While they serve their purpose for fine-crushing, as a preliminary operation in ore-dressing, yet, if ore is to be rolled previous to chloridizing and leaching, Krom rolls are very desirable for finishing, the Cornish rolls serving in that case as roughing-rolls.

Roller-mills, such as the Huntington, Griffin, and Tustin, or discharging ball-mills, such as the Bruckner, while doing satisfactory work in dry- and wet-rolling, are better suited for the mill than the laboratory, on account of the difficulty of cleaning up.

The stamp battery [14 and Fig. 2] is of the California pattern. It has the usual single-discharge mortar for wet-crushing, but only three stamps; the weight of the stamps is 228 pounds; the mortar-bottom is 19¾ by 6 inches; the depth 5 inches; the discharge surface 20 by 10½ inches; the screen-frame 21½ by 13 inches; and the screen-surface 18 7/8 by 9¼ inches. The cams permit the lifting of the stamps to a height of 8 inches. The rate of crushing Nova Scotia gold-quartz with a 7-inch height of discharge, a length of drop of 5¼ inches and 98 drops per minute is 3353 pounds in twenty-four hours, or 1 pound for every 4198 foot-pounds developed. With a 7½-inch drop and 60 drops per minute, it is 2117 pounds, or 1 pound for every 5816 foot-pound. The coarsely-crushed ore is fed to the battery by a Hendy Improved Challenge Ore-Feeder [13]. A double-discharge mortar, of which one side can be closed by an iron plate, will soon replace the old mortar, so that in the laboratory it will be possible to do both dry- and wet-stamping. In planning a new mill a battery with three stamps would not be chosen. The choice would lie between a 5-stamp battery of light stamps, say 300 pounds each, a 1- or 2-stamp battery, the stamp weighing 750 pounds, and a steam stamp. The 5- stamp battery has the advantage that the same number of stamps is used as in common practice. It would not be feasible to have a full size 5-stamp battery, as it entails too much work and requires more ore than is convenient and suitable for experimental work in the laboratory. The 1- or 2-stamp battery with 750-pound stamps dropping in a narrow double-discharge mortar, one side of which could be closed at will, the discharge to be on a level with the base of the die and to be raised by chuck-blocks to 16 inches, and the stamps to have a length of drop of from 4 to 10 inches, would be very acceptable. The results obtained with it would resemble very closely those of large scale work. As to the desirability of a steam-stamp for laboratory use, the writer feels himself at present unable to express an opinion.

The other fine-crushing apparatus, such as the ball-mill, the pan, the sample-grinder, the bucking plate, etc., will be discussed under the heads of sampling and metallurgical apparatus.

Laboratory Particle Analysis Equipment

The sizing or sifting of ore is more tedious in the laboratory than it is in the mill, because the screening surface is necessarily smaller, and all sifting has to be done without the use of water. If there is only a moderate quantity of ore, the sizing is best done by hand on a platform covered with an iron plate [6]. Sieves with wooden frames from 24 to 18 inches in diameter, and iron or brass wire-gauze having from 4 to 20 meshes to the linear inch, are well suited for this purpose. With very small quantities of ore, nests of sieves with metal frames, 8 inches in diameter, and wire-gauze ranging from 20- to 120-mesh are convenient; the screenings to be caught in a metal pan. With large quantities of ore the sifting has to be done by machinery, and the shaking sieves referred to above, are used for this purpose. There are fourteen of these, representing the sizes 2-, 4-, 5-, 6-, 8-, 10-, 12-, 16-, 20-, 30-, 40-, 50-, 60- and 80-mesh. They sift per hour about 2000 pounds of 8-mesh ore, 1000 pounds of ore ranging from 14- to 30-mesh, 300 pounds of 50-mesh, and about 150 pounds of 60- to 80-mesh material. As this work is somewhat slow, it is better to do it in separate sizing boxes. Two inclined boxes having screens of 3-, 10-, 18-, 30- and 60-mesh, and 4-, 8-, 14-, 24- and 50-mesh respectively, are satisfactory for the purpose. They are made of ½-inch pine, are 90 inches long, 18 inches wide and 5 inches deep, and have wooden covers screwed down on a felt band. They are oscillated 200 times per minute by an excentric and connecting rod, which gives them an end-shake. The ore is fed into the hopper at the upper end, and drops on a piece of galvanized iron, whence it passes on to the first (the coarsest) sieve. What is too coarse to pass strikes a dam at the opposite end and is discharged into a vertical spout at the side, to which a cloth bag is attached, through which it passes into a pail. It would seem as if the Coxe gyrating screen, which does such excellent work in sizing all sorts of minerals, might well be suited for laboratory purposes, either in the form of a single screen or a nest of screens. The trommels, as commonly employed in large scale working plants, are out of place in a laboratory. If a trommel is to be used, the polygonal form seems the most suitable, as the different screens could be easily adjusted and removed. It would be necessary in all cases to house the trommel.

Laboratory Hydraulic Classification Equipment

Hydraulic grading is done at present in the Institute laboratory only in an ascending current of water. Grading in a horizontal current of water, or Spitzkasten, will shortly be introduced, as it has been proved to be indispensable for the successful working-up of fine slimes. Now, the fine sands and slimes are only settled, but not graded. Hydraulic classification is practiced with small samples of finely-pulverized ore, as a preliminary test before working small lots. The samples are treated in the Richards pointed tube, where the mixed sands, held in equilibrium by an ascending stream of water are, by slightly slackening the current, drawn off slowly into the glass bulb, which, when filled, is exchanged for another. The contents of each bulb are then separately sifted through a nest of graded sieves, and weighed and examined, to find out just how effective the work has been, and what will be the best sieve-size for the trial-test. In working, the material, after it has been crushed to the proper size, is passed through the automatic feed-trough [8], or the Cornish feeder [7], into a Richards Spitzlutte [9], when the discharge of the spigot will go to the jigs [10 and 11] and the overflow either to the vanner [16] or the slime-table [12], or first to the former, and, as tailings, to the latter. It is proposed to have the overflow, when worked directly on the slime-table, run first over a Spitzkasten, and then to feed separately the spigot-discharge, thus insuring better work. Another way of using the Richards Spitzlutte is to feed only carefully-sized ore, when the spigot, in many cases, will give clean heads and the overflow clean tailings, provided there are no included grains. The capacity of the Spitzlutte with a ½-inch spigot, is about three-quarters of a ton of sized material to 1 ton of mixed material per hour.

The automatic feed-trough and the Cornish feeder serve to convert dry pulverized ore into liquid pulp, delivering it to the Spitzlutte, the jigs or the slime-washers. The feed-trough is of wrought-iron, 10 inches wide at the top, 3 inches at the bottom and 7 feet long, and is placed in an inclined position on a wooden trestle. On the inner side the trough is marked off, so that the same quantity of ore may be washed down by the travelling jet in the same interval of time, which is usually one minute. The travelling jet is a ¾-inch iron pipe, pointed downward and fixed in a wooden truck, having two of its wheels on one edge of the trough and the other on a rail 3 inches away from the opposite edge. The pipe is connected by a rubber hose with the water-main. The carriage is pulled up the inclined trough by a weighted cord, running over a pulley at the upper end of the trough to a shaft near the roof, around which it is wound once or twice and kept taut by the weight. To this weight is fastened a second cord, running over a pulley near the roof to the lower end of the trough, which serves to raise the weight, and thus to lower the carriage. In order to prevent the rubber hose from obstructing the upward travel of the carriage and the even flow of the water, it is suspended from the rail by small grooved wheels, and the loops are replaced by 6 iron-pipe return-bends. Thus the suspended hose shows three zigzags, which are close together when the carriage is at the lower end of the trough, and separate as it travels upward, but are held together at the upper ends by strings, which do not allow them to get more than 24 inches apart.

The Cornish automatic feeder is a four-sided truncated pyramid of sheet-iron. It is 24 inches high, and the bases are 18 and 12 inches square. To the smaller base are attached four legs, on which it stands in a sheet-iron box, 16 inches square and 6 inches deep, contracted at one end into a spout. The legs (pieces of angle-iron) firmly connect the hopper and the box, leaving a distance of ½ inch between them for the ore to pass through. This is charged into the hopper and washed down the spout by a jet of water playing usually between the walls of hopper and box, but occasionally (if especially quick feeding is desired) upon the ore in the hopper.

Laboratory Jigging Equipment

The jigs in use for water-sorting are plunger-jigs and movable sieve-jigs. The former are represented by two Collom jigs [10 and 11 and Fig. 3], used for ores ranging from 30- to 5-mesh, the latter by a Richards jig [17] for sizes larger than 5-mesh.

The Collom jigs are two-compartment machines. They are supported by a V-shaped iron frame on each end. The screen-frames are 12½ by 18½ inches. The length of stroke is adjustable to ¾-inch and the number of strokes can be varied by the use of three step-pulleys, 8, 10 and 12 inches in diameter, from 130 to 180 per minute. The ore coming from the feed-trough, the feed-hopper or the spigot of the Spitzkasten travels over the jig, while the tailings at the opposite end are collected and unwatered in a sheet-iron box. From this they are drawn at intervals, while the water which overflows goes into the water- tanks [18]. The jigs have no automatic discharge for concentrates ; since, for the purposes of instruction and experiment, it is better to stop them every little while and skim off the different layers formed. The manner of working, therefore, is the same as that of large scale one-compartment jigs. The reason for having a two-compartment jig is that “ every machine as far as practicable, should have its guard.” Any middle product not remaining on the first sieve will be collected on the second sieve and thus prevented from passing off into the tailings. The Collom jigs here described were put in to replace two three-compartment Harz jigs formerly in use, the screen-frames of which, 6 by 12¾ inches, were much too small to do satisfactory work. The reciprocating motion was derived from an eccentric adjustable to 2 inches; and the number of strokes could be varied from 100 to 200 per minute by four step-pulleys, 6, 7½, 9 and 10½ inches in diameter. The jigs had an automatic side-discharge for heads.

The movable sieve-jig serves to illustrate the lectures, to work ore coarser than 5-mesh and to do the water-sorting in graded crushing and jigging. The sieve-frame is 14 inches wide, 22 inches long and 12 inches deep; the ore-bed can reach a depth of 10 inches. The rods of the screen-frame, ¾ inch in diameter, are divided into two parts to facilitate taking the machine apart. The two lower or jigging-rods, 48 inches long, are forked at their lower ends and have an eye at the top through which passes a connecting-rod, ¾ inch in diameter, suspended from the upper or excentric rods, which are 25 inches long. The excentrics are adjustable to 2 inches, the excentric-shaft is 51 inches long and 1 5/8 inches in diameter. It has a conical pulley with seven steps, its smallest diameter being 6 inches, its largest 8¼ inches. The number of strokes per minute ranges from 100 to 200. The counter-shaft is placed 14 inches above the excentric-shaft; and the whole is attached to a strong wooden frame. The water-tank in which the ore is jigged is 33 inches long, 27 inches wide and 22 inches deep. Small boards extending from the sides into the tank serve as guides for the screen frame. The hutch-work is drawn off at the sides; the tank rests on a wooden box and its top is 36 inches from the floor.

Slime-Washing

Of the different machines in common use for working slimes [i.e., material not coarser than 30-mesh] only two are represented in the laboratory: a Frue vanner [16] and a convex continuous round table [12] ; a greater variety being excluded by the lack of space.

The Frue vanner is of normal size, i.e., it has an inclined rubber surface 4 feet wide and 12 feet long. Either plane or corrugated belts are used. The normal adjustment for full work in the laboratory [inclination of belt 3½ inches in 12 feet, travel of belt 32 inches per minute, and 195 shakes of 1-inch throw per minute] has to be changed, if the pulp flows directly from the light three-stamp battery upon the vanner, as the battery furnishes only about 1½ tons of pulp in twenty-four hours, while the normal rate of the vanner is 5 tons. The simplest way is to change the inclination to 2½ inches in 12 feet and to regulate the flow of water accordingly. If the vanner is to do full work, the pulp from the battery is collected in the settling- tanks and fed at the required rate and with the necessary water by the Hendy feeder of the stamp-battery. In order to permit this, the connecting-rod of the friction-plate is replaced by an excentric rod, the excentric of which has a 2-inch throw, and is on a small counter-shaft near the ceiling. The counter-shaft is driven from the upper shaft of the laboratory and makes 100 revolutions per minute. The ore which is fed by the carrier-plate is washed by a jet of water into a sheet-iron trough and conducted from behind the mortar into the ore-spreader of the vanner.

The convex continuous round table is 8 feet in diameter and has a slope of ¾ inch to the foot. It is of 1/8-inch sheet-iron, painted with tar, sanded and rubbed smooth, and is supported by an umbrella-frame. It receives its pulp from a fan-shaped distributor, which discharges against one side of a central cone, 14 inches high and 18 inches in diameter, and its wash-water on the opposite side from a horizontal curved pipe with perforations on the inner side. The three products, tailings, middlings and heads, flow into a circular launder. The compartments for heads and middlings are 12 inches wide and hopper-shaped; that for the tailings is 6 inches wide. The heads and middlings are drawn off at intervals into a pail; the water of the heads-compartment overflows into that of the middlings, and the overflow of these into the tailings-launder. The heads are washed off by jets of water; the middlings are sprayed in the usual way. The machine treats from 1 to 1½ tons of ore per day.

There are in the laboratory, of course, the ordinary implements for panning and vanning to check the work done by jigging and slime-washing, and to assist in amalgamating operations.

Electro-Magnetic Separation Equipment 

The magnetic separation of magnetite or of iron-ore rendered magnetic by a preliminary roasting is represented by a small Chase endless-belt machine placed near the tank [32]. This receives the waste-water from a 6-inch Pelton water-wheel which drives the concentrator. Many interesting data of magnetic separation are recorded in the journal of the laboratory. It may be incidentally remarked that a small Pelton wheel forms a most satisfactory motor for any apparatus that is to be driven independently in a laboratory having water under pressure at its disposal. Of course, a pressure-regulator is necessary to equalize the uneven flow obtaining in a city main.

Dry Concentration

There are no arrangements in the laboratory for dry concentration. To make tests that would be in any way satisfactory would require too much space.

Distribution of Power and Water

The machinery of the laboratory is driven by a 15 horsepower upright engine [24] having a common slide-valve. Its cylinder is 9 inches in diameter; it has a 9-inch stroke, and is usually run at 200 revolutions per minute. The main-shaft, 1¾ inches in diameter, is on the ground-floor and runs the entire length of the milling-room. Its position is approximately indicated by Nos. 1 and 3 in the plan (Fig. 1). It makes 240 revolutions per minute. Near the double ball-grinding mill [36.1] it is connected with the countershaft of the same diameter placed near the ceiling. This also runs the entire length of the mill-room along the centerline of the Frue vanner. It makes 200 revolutions per minute. Thus the different machines are set in motion either from the main- or the countershaft, the choice depending upon the location and direction of the belts.

The large dynamo [25], an Eddy shunt-wound machine of 50 volts and 50 amperes, is driven at the rate of 2200 revolutions per minute. It has a separate driving-shaft, 1¾ inches in diameter, making 550 revolutions per minute. The small dynamo [26], also an Eddy machine of 2 volts and 50 amperes, is connected with a counter-shaft, and makes 1400 revolutions per minute. Electricity has so far been used in the laboratory only for the separation of ores and for the deposition of metals. For electric fusion a differently wound dynamo would have to be added, in order to secure the necessary amperage.

The water required in the laboratory is received from the city main, but is not conducted directly to the different machines, since there would be no regularity in the flow. It runs into the end-compartment of the water-tank [18], from the bottom of which a centrifugal pump, 18 inches in diameter, delivers it into a 2-inch main pipe running along the upper platform, on which are placed the machines Nos. 13, 14, 18, etc. Two-inch tees supply the different machines from the top of the main. By the aid of separate pipes and 3-way cocks the overflow from the jigs can be pumped upon either the vanner or the round table, the overflow of the vanner upon the table, and the contents of the settling-tanks upon any of the washing-machines or into the sewer.

Auxiliary Lab Equipment

By referring to the plan (Fig. 1) and its legend, the different auxiliary apparatus used in ore-dressing and in metallurgical work can easily be seen. Prominent among these are, for instance, the steam drying-tables [19], on which the products are dried so as to permit comparison of the weights of ore before and after treatment.

The plan does not show the thirty-odd large bins, 4 feet wide, 4 feet deep and 4 feet high, for ores, fluxes, fuels and intermediary products. They are accessible from the furnace-room by two doors, and from the milling-room by one door.

Laboratory Sampling & Assaying Equipment

Ore-sampling is generally done in the laboratory by hand. If it is desirable to do mechanical sampling, only intermittent machines—those which take the whole of a stream of ore at stated intervals—are allowable. The small-size machines of Bridgman and Constant do good work. Ores are crushed in rock-breakers and rolls and pulverized in the Hendrie and Bolthoff sample-grinder [5] or on bucking-plates [20]. Samples for analytical purposes are ground fine in four Morrel agate- mortars [24.1]. The ores are all sampled by hand on the iron sampling floor [6] or on the sampling table [21]. Liquid pulp, fed upon or coming from washing machines, is passed through specially-constructed automatic samplers (see e.g., Fig. 2). Samples from alloys are taken by chipping, punching, sawing and boring [35]. In laboratory instruction, too little stress is apt to be laid on the sampling of ores and metallurgical products. It is a most important and necessary part of the work, the whole of which is really invalidated if the sampling is inaccurate.

Assaying, in its broadest meaning, includes the quick quantitative determination of any element or compound met within metallurgical work, embracing not only fire-assays but also what is known as analytical work on solids, liquids and gases. In the Institute metallurgical laboratory assaying is restricted to fire-work (except as regards the parting of dore silver buttons or chlorination assays). All analytical work is done in the chemical laboratories. The assay laboratory has two divisions: the assay-room proper [37], and the balance-room [44]. The assay room has eight pulp balances [39], weighing accurately to 1 milligram with a load of 60 grams, and six flux-balances, accurate to 0.1 gram with a load of 600 grams. They are distributed among the students’ desks [38], of which there are fifty. There are twelve crucible-furnaces [41] ; nine muffle-furnaces [40], three of which have lately been erected in “ the space to grow ” [63] ; and, lastly, an iron table [43] for hot crucibles, etc. Under the table is a shelf for crucible and scorifier moulds, and beneath this are small bins for fuels. Along the side of the table are four posts, with anvils for breaking crucibles, hammering buttons, etc. The crucible-furnaces are 27 inches high and 12 by 12 inches in the clear. They are inclosed in wrought-iron plates, and thus firmly held together. The top of each furnace is horizontal, and is covered by a fire-clay tile, around which is shrunk an iron band, with two hooks riveted to it. The cover is suspended from a wire cord passing over a pulley attached to the ceiling, a counterweight being at the other end.

The muffle-furnaces are of different kinds and sizes. Five are Judson coke-furnaces, two with muffles, 4 by 7 inches, closed at one end, and three with muffles 8 by 16 inches, open at both ends; also, three coke-furnaces, with sheet-iron housing and fire-brick lining, having muffles 7 by 12 inches, closed at one end; and, lastly, one two-muffle furnace for bituminous coal, with muffles, 6 by 13 inches, open at both ends. Oil- and gas furnaces are not used. The draft for all the furnaces is furnished by one main chimney [42], 2 by 3 feet, and about 80 feet high.

The balance room contains one analytical balance and nine button balances [45]. The principal aim has been to have the leading makers, such as Ainsworth, Becker, Oertling, Troemner, and others, represented. The balances are accurate to 0.01 milligram, with a maximum load of 0.5 grams.

Metallurgical Laboratory Supplies

While the various operations of the concentration of ores and fuels can be carried on in a school- or general experimental laboratory so as to give practical results, the case is likely to be somewhat altered -when it comes to metallurgical processes. If we take, e.g., a leading process—that of smelting in the blast-furnace, we cannot reduce the operations to a laboratory scale and obtain results that will serve as a guide for practical work. Nevertheless, smelting in the blast furnace ought to be a part of the laboratory work, on account of its educational value. If a student receives for treatment a batch of ore, examines it mineralogically and chemically, makes the necessary analytical determinations of his fluxes and fuel, calculates his charge, smelts it and sums up his results by weighing, assaying, and analyzing the products, he learns more about smelting than any amount of lecturing or cursory visiting of works can ever teach him. Only by taking hold himself and carrying a process through to the end, can he learn how to think metallurgically, and thus become really qualified to listen intelligently to what is taught in the classroom.

There are, however, many metallurgical processes—such as roasting, amalgamating, leaching, electro-deposition, and other operations—which can be performed in the laboratory on a small scale with trustworthy economic results. In fact, the engineer is guided, in the planning of amalgamating- and leaching-mills, by the results obtained in such laboratory experiments. This class of work should therefore have a prominent place in the laboratory. From what has been said, it will be evident that most operations relating to the metallurgy of iron and steel must be excluded. Attempts have been made to imitate large-scale iron and steel work in the laboratory. For instance, the Sheffield Technical School, in England, has a small open-hearth steel-furnace; the Polytechnic School of Aix-la-Chapelle, Germany, has a small puddling-furnace; but the writer, though not acquainted with the results obtained, is much inclined to doubt whether they will be found to justify the large outlay of time and labor involved. We must always keep in mind that it is not the province of an engineering school to perfect the student in any one branch of his profession, so much as to ground him in the fundamental principles upon which he is, later, to build for himself in detail.

In the laboratory of the Institute, the processes chosen for instruction are those involved in the treatment of lead-, copper-, gold- and silver ores and the ores of some of the minor metals, although it should be added that crucible-work and other small-scale heat-treatment of iron and steel, especially with regard to their physical properties, are not excluded.

The furnace-room [48] contains apparatus enough of various kinds to carry on all the necessary operations, so arranged as to occupy as little space as possible. This forces a crowding of the furnaces; but as the work can be so laid out that adjoining furnaces need not be used at the same time, fewer inconvenience results than might be at first supposed. The necessary draft is furnished by a stack [84] 2 by 3 feet and about 80 feet high. A horizontal main flue, 3 by 3 feet, running along three sides of the room—sometimes near the ground, sometimes near the ceiling, according to the height of the furnaces —collects the gases. Each furnace, however, can be shut off from it by a damper in its branch-flue. Too much stress can hardly be laid upon the necessity of securing a strong draft. The main and branch-flues should be large, and the stack of ample section and sufficient height, so that it shall be possible to run each of the furnaces alone or any number or all of them together. With a well-fitting damper, it is an easy matter to cut off too much draft; if it is too little, the result is fatal.

Laboratory Roasting Equipment

For this purpose, there are three reverberatory furnaces and one stall.

The large hand-reverberatory [56] covers 8 feet 2 inches by 5 feet 7 inches and is 4 feet 8 inches high. Its hearth is 4 feet 2 inches long and 3 feet wide and lies 9½ inches below the top of the fire-bridge, which is 9 inches wide. The height of the 9- inch side wall is 11 inches to the spring of the arch, the height of the arch 5 inches. The furnace has one working door, 14 by 9 inches in size, and 2 feet 10 inches from the ground. The gases pass off through three openings, 9 by 9 inches, in the roof, into a branch flue running across the furnace and ending in the main flue. The fireplace, 2 feet 3 inches by 1 foot 9 inches, lies 16 inches below the top of the bridge, which is 8 inches below the roof. It has a door 12 by 9 inches in size, and 2 feet 6 inches from the ground. The furnace treats charges of about 250 pounds of pyritic ore.

The outside dimensions of the small hand-reverberatory [60] are Length, 8 feet; width, 2 feet 8 inches; height, 5 feet. The hearth is 2 feet square and 6½ inches below the top of the bridge, which is 3 inches wide. The height of the 4½-inch sidewall is 8 inches to the spring of the arch, and that of the arch is 5½- inches. The working door is 9 by 6 inches, and 2 feet 10 inches from the floor; the flue running over the furnace is 5 inches square. The fireplace, 1 by 2 feet, is 10 inches below the top of the bridge, which is 7 inches below the roof; and its door, 9 by 6 inches, is 2 feet 6 inches above the floor. The furnace works small charges of, say, 25 pounds of pyritic ore.

The drawback of roasting in such small reverberatories is that the charge is liable to become too much cooled near the working door. If there had been more room, both roasting- furnaces would have been constructed, like the reverberatory smelting furnace, with the working-door at the end and the flue just above it; the air necessary for roasting being admitted through the hollow bridge. It might also be an improvement to have the hearth built in an iron pan, and so arranged as to permit its being removed, cleaned, and examined after an operation; although this is not so necessary in roasting as in smelting.

The third reverberatory roasting furnace, the Bruckner cylinder [54 and Fig. 4], gives an opportunity to study the behavior of ore on a revolving hearth. The outside dimensions are: Length, 6 feet, and diameter 2 feet 8½ inches. The cylinder is of 3/16-inch boiler-iron and has a 2½-inch fire-brick lining. The throat is 12 inches, and the charging-hole 8 inches in diameter. The cylinder, the axis of which is 3 feet 5 inches above the ground, revolves on two iron friction rings (35 inches in diameter) which rest on four 12-inch carrying rollers. One of the carrying-roller shafts (2 7/16 inches in diameter) is rotated by a worm-gear (62 teeth of 1-inch pitch) at the rate of 20 revolutions per hour. The fire-box is detached and rests on castor wheels. By moving the box backward or sideways, the amount of air admitted can be increased. An additional improvement would be to make the throat of the fire-box muffle-shaped, leaving that of the furnace circular. In order to have complete control over the flame, the grate (18 by 24 inches) is laid 20 inches below the bridge. The carbonic oxide gas generated is burned by warmed air entering the furnace just above the bridge, after having been forced through five flues in the side-wall and roof of the fire-box. The ash-pit, 8 inches deep, is closed and connected with a blast-pipe. This furnace treats charges of about 200 pounds.

The stall [57], which completes the roasting apparatus, is commonly used for treating coarse copper-bearing pyrites previous to smelting in the blast-furnace. It is 3 feet 3 inches deep, 2 feet 3 inches wide and 3 feet 7 inches high to the spring of the arch. The arch is 6 inches high. The walls are 4 inches thick and well anchored. The ore is roasted on a temporary grate of wrought-iron bars. The front is bricked up half-way, the upper half being closed by an iron plate with peep-hole. The charge varies from 1500 to 2000 pounds, and a roast lasts from two to three days. The results in desulphurization are very similar to those in large stalls. The management of the stall affords a splendid lesson in the regulation of draft.

Laboratory Smelting Equipment

Smelting is carried on in the blast-furnace, the reverberatory furnace and the crucible-furnace.

The blast-furnace [52 and Fig. 5] has had to undergo several changes before it reached the present satisfactory form. The first furnace, 18 by 15 inches at the tuyere level, was built of brick. It had one tuyere at the back, run with a “ nose,” the ore being charged towards the back and the fuel towards the front. It would last one day, or perhaps two days, and then had to be relined. The next furnace, 18 by 16 inches, with three ordinary tuyeres, and charged in horizontal layers, burned out in less than a day. When provided, however, with one water-cooled tuyere at the back, projecting 8 inches, it was run successfully, and had to be relined only once a year. With this furnace ores were smelted for about six years, until, in 1884, the present one replaced it. This is a water-jacket furnace, resembling the circular copper-smelter in common use to-day. The height of the furnace, 6 feet 6½ inches, is divided as follows: height of four hollow cast-iron columns, 17½ inches; thickness of annular collar, 1 inch; distance to tuyeres, 1 foot; diameter of tuyeres, 2 inches, and height to feed-door, 3 feet 10 inches. The diameter at the bed-plate is 1 foot 5 inches; at the tuyeres, 1 foot 6 inches; at the throat, 1 foot 11 inches. The furnace has a conical hood 2 feet 9 inches high and 25 and 11 inches in diameter, which ends in a vertical flue leading into the main flue. The feed-door is 13 inches high, 14 and 9¾ inches wide. The water jacket is of 3/8-inch boiler iron and has a 3-inch water space. The feed-water is supplied from the city main through a ¾-inch pipe near the top, the overflow pipe being tapped into the upper flange. There are four tuyere- holes, lined with solid bored blocks of bronze. The tuyere- pipes are of wrought-iron steam-pipe; the horizontal arm has at one end a conical turned bronze nozzle, at the other a T, the vertical leg of which is connected by a pipe with the tuyere- bag, and the horizontal leg, reduced in diameter by a bushing, is closed with a cap having a glass-covered peep-hole. The bustle pipe is 4 inches in diameter. The bottom of the furnace is closed by a wrought-iron plate clamped to the collar of the four columns. The crucible is lined with brasque tamped in solid from above to the level of the tuyeres and then cut out from below into the desired shape, the lining reaching up to the tuyeres.

In tapping the melted masses from the furnace different methods were tried before the present one was adopted. With an internal crucible and separate metal- and slag-taps the metal easily became cool; with an external crucible and continuous flow, it cooled even more quickly. The present practice is to tap the melted masses into a small cast-iron overflow-pot, having the form of an inverted pyramid, 6 inches deep, 12½ inches square at the top and 2½ inches square at the bottom. This retains the metal, matte and foul slag, and is removed after every tapping by means of iron hooks inserted through rings on either side. The clean slag overflows into an ordinary conical slag-pot, 14 inches in diameter and 16½ inches deep. A detached carriage serves to take away the full pots and return the empty ones. A Devereux slag-pot may in the future replace the arrangement now in use. The fumes from tap-hole and slag-pot are drawn off by a hood connected with a small fan. The furnace has a daily smelting capacity of about 6 tons of charge, not counting the fuel. It is not run, however, for 24 hours at a time. The furnace, warmed during the preceding day and night, is usually blown-in at 8 A.M. and blown down again about 4 P.M. This period is sufficient to give the student all the instruction that he can get from carrying on a smelting operation on such a small scale. Longer runs would mean greater physical exertion without corresponding benefits. When a run is completed, all the products are carefully separated and, if necessary, the matte adhering to foul slag or metal is separated by an additional crucible fusion, and thus a complete account of stock is taken. With the present arrangements, the loss of metal in flue-dust has to be arrived at indirectly by difference. It is proposed, however, to save the flue-dust, either by cooling or filtering or by wet condensation and thus to obtain direct figures.

Three reverberatory smelting-furnaces were once considered necessary to fill the wants of the laboratory for agglomerating lead and copper-ores, smelting lead-ores, cupelling base bullion, bringing forward matte, and refining copper. Two furnaces are sufficient. The English cupelling-furnace [59] serves for the last three operations; while the other two, formerly carried on in a reverberatory furnace (replaced today by the Bruckner cylinder) will be taken up again when the copper-refining furnace [55] has been rebuilt as a reverberatory furnace with movable hearth inclined from bridge to flue. The cupelling furnace is of the ordinary pattern. The test is 18 by 24 inches, and is wedged fast against the test-ring; the fire-place, 18 by 24 inches, is run with the under-wind; the grate is laid low, 20 inches below the top of the bridge, which is 9 inches wide and 15 inches below the roof. In order to burn the carbonic oxide gas formed, there is a special tuyere in the side of the furnace just above the level of the bridge. In addition to the tuyere at the back of the hearth, there is a second one in the roof connected with a U-shaped pipe passing through the flue. The hot blast comes into play when a quick raising of the temperature is desired. The different kinds of reverberatory work so far practiced in this furnace, such as liquating drosses on an iron plate, softening and cupelling base bullion on a hearth of limestone and clay, concentrating matte and refining copper on a hearth of a mixture of raw and burnt fire-clay or closely-fitted refractory tiles have been so satisfactory that the idea of a fixed hearth for laboratory-purposes has been entirely given up. In the furnace 150 pounds of base bullion, assaying about 150 ounces of silver per ton, are cupelled in 6 hours, or 200 pounds of black copper are brought through the different stages to tough-pitch copper in 7 hours.

The plan, Fig. 1, shows a small cupelling-furnace [61], which is used sometimes to refine impure silver from the English cupelling-furnace in quantities larger than can be satisfactorily treated in one of the muffle-furnaces. It has a small fire-place, 8 by 14 inches, and 15 inches deep, the flame rising from which strikes the fire-clay tile forming the roof, and is deflected so as to strike the silver (placed in an oval cupel-test, 8 by 14 inches, and 2 inches deep, filled with bone-ash).

Crucible work is of considerable importance in a metallurgical laboratory, as it is not only adapted for independent experiments but serves to bring into suitable form the different mixed products obtained in the processes carried out on a larger scale in the laboratory. Small crucibles are commonly heated in the assay-furnaces; for larger charges, there are two pot-furnaces [62, and Fig. 6], worked with under-wind. They are 14 inches square and 23 inches deep; the blast is introduced through the ash-pit door, and the ash-pit is 9 inches deep. A furnace holds conveniently a No. 35 graphite crucible.

Distillation and Sublimation

Both these operations are of subordinate importance in laboratory work. Distillation of mercury is carried on in half-pint and one-pint bulb-retorts, which are heated over four-tube Bunsen burners. The delivery pipe is cooled by suspending from it an iron trough filled with cotton waste, which is kept wet. Reduction of zinc oxide or sublimation of arsenic, realgar, and sulfur are rare operations, and no special apparatus is assigned for this purpose.

Crystallization

The principal process coming under this head is the Pattinson process, for which a cast-iron kettle [58] is used, 21 inches in diameter and 14 inches deep, covered with a hood and heated by a fireplace 21 inches square. This kettle is rather small for the Pattinson process; it is the one in common use for desilverizing argentiferous lead by the Parkes process, and for melting and liquating, in general, readily fusible metals and alloys.

Laboratory Leaching Equipment

The leaching of ores and intermediary products can be done in the laboratory in stationary vats by percolation, or by mechanical stirring, or in revolving barrels. For leaching by percolation, there are two forty-gallon vats (not shown in the plan, Fig. 1) of wood lined with lead. These will be replaced with sheet-iron vats poured with melted roofing pitch. For leaching in stationary vats with mechanical stirring there are three sets of 8-gallon vessels [28 and Fig. 9] of glazed earthenware, 12 inches in diameter and 14 inches deep. The wooden stirrers, with their iron driving shafts, make 75 revolutions per minute. For leaching in a revolving barrel the same apparatus is used as for amalgamation. Gold-, silver- and copper-ores are commonly, and zinc- and nickel-ores occasionally, treated by wet processes in the laboratory.

Electro-Metallurgical Work

Electricity has so far been used only for the refining of silver- and gold-bearing copper. The large depositing table [27] holds the electrolytic baths. They are of wood-pulp, poured with melted roofing-pitch, of glass or of earthenware, as the case may be. No definite sizes have been, so far, adopted, but electrodes are usually made 7 by 10 inches. The current is furnished by the dynamos already referred to; thermopiles and storage batteries are not in use.

It is somewhat difficult to estimate the cost of the laboratory- apparatus, because one thing has been put in after another, and alterations have been frequently made.

That it is conducted in connection with classroom work, and not independently, need hardly be mentioned. With the school- courses of the fourth year the students are thoroughly trained in the laboratory, their work there supplementing and illustrating the lectures. The last term is largely devoted to the working up of theses, which are always founded on laboratory-experiment. While the student does not handle every apparatus, he sees most of them in operation. Every Saturday each student makes, before the assembled class, an oral report of his laboratory-work during the past week, and its continuation for the coming one is discussed and laid out. The whole class thus gets the benefit of the work of each individual member. The time devoted to laboratory-work is 325 hours, and to classroom work, including preparation, during the same year, 225 hours. The most satisfactory arrangement would be to have during the entire year two days a week for laboratory-work. One of these should be uninterrupted for making a complete experiment, the other might be divided into two half-days.