MAY 29, 1891.]

where stability begins. But here it leaves the ascending branch because it takes less strength of field to hold them in this position than it required to put them there. This state continues until the field is of nearly zero strength, when two or three magnets turn, giving the small drop at e. A slight negative increase turns many more, and another reverses every remaining magnet except four, which are almost exactly opposite to the direction of the field. In fig. 1 the

Top.

Middle.

683

case of steel, fig. 5 represents soft iron-that is, the case in which there is a less intimate connection of the molecules in their respective groups.

At b a small cycle was superposed upon the main cycle, as shown by the small loop. At e the loop returns to the main curve. If one of these minor cycles be performed at a point like d, which represents a stable position of the magnets, the curve merely retraces itself, illustrating the fact that there is no hysteresis without passing through a position of instability. On the contrary, at a point like e, where nearly half of the magnets have just turned, the area is very large. It is interesting to note that the curve took a new track at g instead of returning to e.

These are a few of the curves which have already been obtained from the model. They are necessarily very imperfect, largely on account of the relatively small number of magnets used. They suffice to show, however, the close resemblance of the model to actual magnetic metal, as far as the most important properties are concerned, which was all that was originally expected.

Bottom.

THE

Direction of magnets corresponding to the curve in fig. 2.

FIG. 4.

increase from f to g turned these four, but in,fig. 2 they were not affected by the strongest current that could be used. Consequently the curve of fig. 2 is almost horizontal between f and g. The difference was probably due to a slight change in the position of the plate which supported these magnets. Completing the cycle, the upward branch of fig. 1 is seen to consist of two main steps, while fig. 2 has three, and both curves are to the right of the origin.

These curves may possibly represent one group of molecules in a steel bar. Since the mean density of steel is nearly the same as that of iron, it appears that the large hysteresis of the former is due to the molecules in individual groups being nearer, the groups themselves being further apart than in soft iron. To diminish the hysteresis of the model, the magnets

must be placed further apart in order to lessen the stability of their positions. The area of the curve can thus be decreased indefinitely. The curve of fig. 5 was taken with the magnet centres 2 inches apart-that is, with the magnet ends inch apart at the closest. In this curve the cycle was performed in the opposite direction to that of the others. The last downward branch is dotted to distinguish it from the first. The area of the curve suggests at once that if figs. 1 and 2 represent the

ELECTRICAL

TRANSMISSION AND CONVERSION OF ENERGY FOR MINING OPERATIONS.†

By H. WARD LEONARD.

THE transmission and conversion of energy is, above all others, the question of importance in every kind of engineering work, and in mining engineering this is most conspicuously true.

Until quite recently all practical methods of transmitting and converting energy involved the actual transfer of sensible matter over the distance in question and this matter necessarily possessed such qualities as weight, magnitude, temperature, inertia and other qualities common to all matter.

It is, therefore, not surprising that all engineers, and particularly mining engineers are watching with the keenest interest the development of methods for transmitting and converting energy by means of electricity, for, in electrical problems, the many considerations and restrictions due to the inflexible characteristics of matter may be entirely disregarded and the possibilities of mining engineering are correspondingly increased.

The transmission and conversion of energy by water, steam, cables, compressed air, and so forth, we are all familiar with, and we know to our sorrow the limited distance, the low efficiency or the tremendous first cost which has hampered our engineering work at every turn.

With the utilisation of electricity for the transmission and conversion of energy we absolutely reverse these conditions and are enabled to operate at practically unlimited distances, with extremely high efficiency and very low first cost.

The invention of the incandescent lamps marks the commencement of an era upon whose threshold we now stand and in which the possibilities of engineering will be extended to a degree we can, at present, have no adequate conception of. Until the Edison lamp was invented and introduced, all distribution of electrical energy was by what is known as the series system, which did not lend itself readily to the development and use of electric motors. With the Edison lamps came the system of distribution on the multiple arc plan, and the commercial possibility and development of electric motors dates from that time.

The stationary electric motor supplied from the lighting circuit was naturally the first on account of the number and simplicity of its applications; then the motor was applied to propelling street cars, and the modern electric street railway system was rapidly evolved. The electrical engineer, in his search for "new worlds to conquer," next turned his attention to the mining field.

The great variety of the applications in this field, the distances from the mines to the principal cities where electrical developments have been most rapid, and the lack of knowledge as to the exact requirements have, until recently, made even the simplest applications of electricity to mining rather rare.

Perhaps the greatest stumbling block has been the percussion drill. Until recently, when a mine owner asked if we could transmit his power, light his mine and operate his pumps, hoists, tramways and mills, we could confidently reply "yes"; but when he asked if we could replace or operate his air drills we were obliged to say "not yet."

Since the drill is the most universal of all mining appliances operated by power other than hand power, it was not possible to make rapid progress until this deficiency was corrected.

The Edison General Electric Company has put upon the market in commercial form, during the past 30 days, three types of electric drills which will enable the mining engineer to accomplish all that he has been able to accomplish heretofore by other drills, and not only this but to accomplish far more than was heretofore possible and under conditions heretofore prohibitory.

Lord Rayleigh, Philosophical Magazine, March, 1887.

† Read before Association of Mining Engineers of the Province of Quebec, April 29th, 1891.

684

First in importance comes the electric percussion drill, the invention of H. N. Marvin, of Syracuse.

Following is a brief description of the principal features of the drill:

Fastened upon a suitable tripod or column is a piece of boiler tube 7 inches in diameter and about 24 feet long. In the forward half of this casing are placed two cylindrical coils of wire in the form of solenoids, each about 8 inches long, having an outside diameter of about 6 inches, so as to make a loose fit with the casing, and an inside diameter of about 24 inches. These two solenoids are placed so as to be against each other end to end in the casing. The bit plunger plays freely through the centre of these solenoids, and is supported by two bearings placed just beyond the outside ends of the two solenoids respectively. The back portion of the casing contains a spiral spring of the form frequently used for car springs. The plunger is composed of a central portion made of wrought iron, about 14 inches long, and both the forward and back portion of the plunger, which are made of aluminum bronze, are rigidly fastened to this iron portion. The forward portion is about 13 inches long, and carries the bit socket. The back portion is spirally milled for a length of about 9 inches, so that the cross section of this portion is hexagonal. At the extreme back end is a steel buffer which strikes against the cushioning spring.

The spirally milled portion of the plunger is similar to that used in other purcussion drills, and causes the drill to revolve upon its axis one-sixth of a complete turn with each stroke. The ends of the coils of wire are brought to contact pieces at the top of the adjacent ends of the two solenoids, where there is a socket for receiving the terminals of the cable and thus making electrical connection with the drill. There are three conductors leading from the generator to the drill, one of which is connected to one terminal of each of the solenoids, and the other two conductors are connected to the two remaining terminals of the solenoids respectively.

The generator is of the simplest kind, the coils on the armature having their terminals connected to two insulated collars on the shaft.

One collar is a continuous metallic ring, and upon this one rests a brush which is connected with the conductor, which is common to both solenoids. The other collar is metallic for half of the circle, and the remaining half is insulated from the armature wires. Upon this half ring rest two brushes diametrically opposite each other, and each brush is connected to one of the two remaining conductors leading to the solenoids in the drill.

If we now revolve the armature of our generator in a separately excited magnetic field, an electric current will flow, let us say, from the armature to the half ring, then through one of the two brushes which happens at the instant to be in contact with the half ring, along the corresponding conductor to one terminal of one solenoid, let us suppose the rear one. Then through the rear solenoid itself and back along the mutual wire to the continuous ring and then to the armature again.

This current in passing through the rear solenoid makes a powerful magnet of it, and this tends to pull the plunger back into a position such that the centre of its iron pection shall be in the centre of the rear solenoid.

When the armature moves forward a half revolution, the polarity of its wires is reversed, and the other brush with its conductor is now in contact with the half circle. Consequently, the current in the mutual wire will be in the reverse direction from that of the former wave, the rear solenoid and its conductor, formerly active, are now out of circuit, and the circuit is made through the other conductor and its corresponding solenoid, that is, the forward solenoid.

The magnetic action of this solenoid now tends to make the plunger move forward so that the centre of the iron portion shall be in the centre of the forward solenoid.

Thus we get a reciprocating action of the plunger, and every revolution of the armature of the generator will cause a complete stroke of the drill. By varying the speed of revolution of the generator we can make the drill strike any number of blows per minute we choose. In usual practice 600 blows per minute is found to give excellent results. The spiral spring, it will be observed, stores up the energy of the back stroke and returns it to the forward stroke, assisting the magnetic impulse and greatly increasing the strength of the blow.

In order that we may form an unbiassed judgment of this drill, I will quote the opinion of Andre, perhaps the best authority on power drills, and who many years ago stated the requirements of a first-class power drill to be as follows:

1. Simple in construction, strong in every part.

2. Few parts, especially moving parts.

3. As light in weight as can be made strong.

4. Take up little space.

5. Striking part of relatively great weight and strike directly.

6. Piston alone exposed to shocks.

7. Piston capable of variable length of stroke.

8. Sudden removal of resistance should not injure any part.

9. The rotary motion should be automatic.

10. The feed of machine, if automatic, should be regulated by the advance of the piston as the cutting advances.

11. Should be capable of working with moderate pressure. 12. Should be readily taken to pieces.

It may be sufficient to say that the Marvin drill possesses every one of the good qualities Andre specifies, and in a most marked degree; but, in describing the good qualities of this drill, we can, if necessary, add considerably more than Andre specifies, for example:1. It is simple in construction and strong in every part. 2. It has a minimum of moving parts, that is one.

:

3. It is very light in weight for its strength, this being possible because of the perfect cushioning at both ends of the stroke. 4. It takes up very little space.

5. The striking part is of relatively great weight and it strikes directly.

[MAY 29, 1891.

6. The length of the stroke is variable at will. 7. The drill cannot damage itself by its own blow. 8. The rotary motion is automatic.

9. It has very few parts.

10. It can be entirely taken apart and put together again inside of ten minutes.

11. There are no joints to be fitted or packed.

12. It is not affected by heat or cold.

13. It can be operated at great distances from the source of power. 14. It has a much higher efficiency than other drills. 15. It is independent of the action of any valve.

16. The rate of striking is independent of the kind of material it strikes.

17. It will operate in the open air without striking anything, and hence can be made to strike an extremely light blow at its full rate, which is very important in starting holes, and so forth.

18. It can be rapidly moved from one position to another at a great distance, since the energy is transmitted through flexible cables. 19. No loss is suffered due to elbows, bends, valves, and so forth, in the conductors.

20. The conductors can be carried on very light supports, both because of their light weight and because the transmission of energy through them does not tend to distort their position.

The importance of the above characteristics will be apparent to any one who is familiar with the operation of the steam and air drills. It is interesting to note that in driving the Hoosac Tunnel the average life of the power drills, before sending them to the shop, was 50 hours. Even to-day, after a development of 25 years, we find that it is common practice to have in the shop one half the total number of drills employed.

In pushing engineering work it is frequently of paramount importance that the work be done quickly. Therefore, any means of greatly increasing the rate of drilling is extremely valuable. To increase the rate of drilling, we must either increase the strength of each blow or else we must increase the number of blows per minute. A limit to the rate of striking is soon reached when a valve of considerable weight must be moved from rest by the concussion of the previous blow, and when a material substance, such as air or steam, must then fill the space back of the piston and raise the pressure to the working pressure. Also the strains and shocks caused by the valve and the air or steam soon become troublesome as we increase the rate of striking. With the electric drill the speed of rotation of a perfectly balanced cylindrical armature of small diameter has no such limitations, and there is apparently no limit to the rate of striking, except the magnetising and demagnetising of iron, which is already done in daily commercial practice at the rate of 10,000 times per minute with the highest efficiency.

With 800 blows per minute we have already drilled, at the rate of 4 inches per minute, a hole 1 inches in diameter in the hardest Quincy granite, and that with an expenditure of energy not exceeding 3 horse-power.

I firmly believe that in a comparatively short time we will be furnishing percussion drills whose rate of striking will be several times as much as that we now employ, and that with no more and no heavier drills than are now used, the rate of driving a heading will be increased many times. The importance of rapid driving of work is practically illustrated by the fact that in driving the Sutro Tunnel. Mr. Sutro offered the men at work, in addition to their regular wages, the following bonus :

For every foot per month over 300 and under 400

400 500

$5. 500 $10. $20.

A bulletin from the Census Department, under date of March of this year, shows that in granite quarrying the cost of labour is 64 per cent. of the total cost of production; and in Massachusetts, where the output is much greater than in any other State, and where the longest experience and most approved methods are met with, the labour is 82 per cent. of the total cost. It will be evident that any labour-saving device in such a field will be extremely valuable.

Another drill of great value to the mining engineer is the diamond drill. The Edison General Electric Company have, during the past thirty days, put upon the market an electric diamond drill which they have been developing for the past two years. The drill is the invention of I. E. Storey, of Denver. It presents a great many advantages over the diamond drills heretofore used, as will be evident from the following description of it :

The drill weighs complete 239 pounds. The average power er consumed about 13 H.P., and with this expenditure of power the drill will bore a hole of 14 inches diameter in hard rock at the rate of 2 inches per minute, taking out a core of of an inch. The drill rod is rotated at the rate of 400 revolutions per minute without any load, and when drilling at full load the speed is practically the same.

The drill rod is geared by a single set of gears to an electric moter which revolves at 1,600 revolutions under conditions of full load The motor has four poles, and the keeper joining the poles is in the shape of a surrounding cylindrical shell, which thoroughly protects all the parts of the motor and other parts of the machine.

Upon the drill rod is placed a rotary pump which supplies the drill with the necessary water.

In using the diamond drill the following points are of great importance:

1. The speed should be uniform and automatically controlled very closely, so that removing the load quickly will not permit the drill to

REVIEW

4. The drill should be as light and compact as is consistent with the requisite strength.

5. The drill should be capable of being readily and rapidily moved considerable distances, and put into operation again with the least loss of time.

Up to the present time diamond drills are operated by reciprocating engines, and the engine is fastened upon same frame as the drill rod to which it is geared by suitable gearing. The engine usually has two cylinders of the oscillating type to reduce the vibration as much as possible and eliminate the dead points. With these small engines it is practically impossible to automatically get the close regulation of speed which is desirable, and hence the speed is governed entirely by hand throttling, and the engines cannot be run at very high speed because of the vibration they would produce, and because of the rapid depreciation of such engines at high speed. It, therefore, becomes necessary to gear to the drill rod by gearing which is oftentimes objectionably larger and would become even more so if a higher speed upon the drill rod were attempted, as is desirable. The space occupied by the drilling machine is quite as large as the engine gears, and so forth, occupy much space. This is a great objection in cases of operation in tunnels, shafts, and so forth."

With the electric drill the motion is free from any jar, as there are no reciprocating parts, and the speed can be made absolutely constant under any condition of load up to the full load. The speed of the drill rod can be made anything desired up to several thousand revolutions per minute if desired, and under any conditions of speed above 1,600 per minute there would be no gears whatever. weight of the electric diamond drill is for the same power much less than that of the steam diamond drill, and the space occupied is in a direct line with the hole and is extremely small in amount.

The

The drill can be operated from any existing electric light circuit, and the current for it can be supplied at two miles distance from the source of power by wires of size 10 B.W.G. having a diameter of about 4th of an inch. The drill can be carried whenever a man can

carry 35 pounds, which is the weight of the heaviest single piece, and hence can be set up and operated in the most inaccessible places.

It will be evident that for prospecting work, when a certain territory is to be explored, this drill is particularly adapted.

Starting from a convenient and economical source of power, we can, if desirable, lay our wires along the surface of the ground, and in a very few hours can be operating our drill miles off. We can then reel up our wire and lay it again in an exactly opposite direction, and again be in operation at perhaps five or ten miles off in the course of a few hours more. In laying the wire a couple of horses yoked abreast and carrying a reel is all that is necessary. For operating at a distance of one mile in any direction, the diameter of the wire necessary is but th of an inch, and the total weight of the wire only 340 lbs.

The facility with which prospecting and also drilling in permanent works, such as mines, can be done with this drill will no doubt lead to its rapid and general use.

There is every reason to expect that with the electric diamond drill the speed of the rotation of the drill can be very greatly increased with consequent increase in the rate of drilling, which is of the greatest importance.

The Edison General Electric Company have a third kind of drill, which is a rotary high speed drill, having a solid steel bit, and this drill is used for drilling coal and similar comparatively soft materials and also for drilling metals, where it will have an extensive use in the construction of steel ships and bridges and similar works, where the drill has to be taken to the work rather than the reverse.

With the three drills which I have described, the Edison Company is now able to do any class of drilling desired, and these drills are likely to lay an important part in the future of mining engineering. The electric mine locomotive and the hoists, pumps, ventilating fans, crushes, stamps, and so forth, operated by electricity are instances of the application of electricity to mining which have already proved themselves entirely successful. The under-cutting of

coal by electricity is an important field in which the Edison Company has made great strides, the machine being of two entirely distinct types, which becomes necessary in order to properly comply with the conditions met with in practice in different mines.

The electric refining of metals, especially of copper, is an extremely interesting subject to the mining engineer. The Edison Company have established the majority of the plants of this nature in the United States; and I need only say that the results are highly economical and most satisfactory in every way.

The electrical transmission and conversion of energy at great distances is destined to come up in nearly every mining problem in the future. Mines are usually in a mountainous country and it is seldom that a water power cannot be found within a few miles of a mine. The mining engineer in the immediate future will develop this water power, convert its energy into electric energy, in which shape he will transmit it to the distant mine, when it will be again converted into the various forms of energy which he may have occasion to require.

Among the applications will be the following:

1. The lighting of the mines and the buildings and grounds by arc and incandescent lamps.

2. The operation of any machinery in the mill, such as crushers,

stamps, and so forth.

3. The operation of the drills.

4. The operation of the hoists.

5. The operation of the pumps.

6. The operation of an electric tramway in the mine.

7. The operation of ventilating fans.

8. The heating of the buildings when fuel is scarce.

9. The refining of copper and recovery of gold and silver in certain

conditions of highest economy and minimum first cost; and some years ago I investigated these questions and deduced formulæ expressing these laws.

These formulas are given in tabular form in the accompanying Sheet I. I have also expressed the laws governing the conditions of minimum initial cost graphically in Sheet II.

It may be interesting to note here in passing, a fact which you will observe by examining the formule given, namely: If we pay proper attention to the laws governing the highest efficiency and the least first cost, the cost of the conductors for the plant will depend solely upon the initial E.M.F. and the distance. Thus under practical conditions to-day, if we are to operate with 2,000 volts E.M.F. at a distance of 5 miles, the minimum first cost would be realised when we operate with a loss of 20 per cent. in conductors. The cost of copper (at 20 cents per bl.) for each horse-power delivered at the motor brushes under those conditions would be $7.47. This simple but invariable law, which is embodied in the formulæ given herewith, you will find of great assistance to you in considering questions of electrical transmission.

You will also notice that the formulæ show that, for any given

percentage of loss, the electrical pressure to be employed will vary directly with the distance. Thus, for 20 per cent. loss the cost of copper being $11.20 per horse-power delivered at motor brushes, the E.M.F necessary for transmission of 16,000 feet will be 1,500 volts. at 32,000 feet we should use 3,000 volts, and at 8,000 feet 750 volts In order to secure the 160 H.P. necessary at our various devices in and about the mine, we must deliver 300 H.P. to our main motor in the form of electric energy in the conductor at the brushes of the motor. With 25 per cent. loss in conductors this will mean 266 H.P. at the generator brushes or 300 H.P. delivered by the water wheels For the sake of reliability and economy we will use two generators instead of one, each being of 133 H.P. At the mine there will be two main motors of 90 H.P. each, wound for 900 volts and 89 ampères producing a total of 180 H.P., which will drive the drill generator of

17 H.P., and a generator of 250 volts and 300 ampères for operating the incandescent lamps, the arc lamps, the locomotive, the hoist, the pump, the diamond drills, and the heating. The main motors will also supply the milling machinery with the necessary 30 H.P.

By formulæ on Sheet I., we find that to transmit 180 H.P. 3 miles with 25 per cent. loss, and an initial pressure of 1,200 volts, there will be required a wire having a circular millage of 190,000 circular mils.; this is having a diameter of 436 thousandths of an inch, or a little less than half an inch.

We find that by other formulæ on Sheet I., that the copper will weigh 20,000 lbs., and will cost $4,000, which results check each other and prove the accuracy of the calculations.

We are now able to make an estimate for the total plant, as follows:

Estimate of cost of plant for transmitting 180 H.P. a distance of 3 miles, with a loss of 25 per cent in conductors, the plant to comprise the apparatus as specified.

Developing original water power and installing water
wheels of 300 H.P.

$15,000

...

2 generators, 100 k.w. each (1,200 v.-83 amp. each)

at $36 per k.w.

2 motors, 75 k.w. each (900 v.-83 amp.) at $36 per k.w.

7,200

5,400

Copper, 32,000 feet, 4000 B.W.G.

4,000

1 6-drill generator

1 generator of 250 v., 300 amp., 75 k.w. at $36

2,700

6 electric percussion drills

3,300

2 electric diamond drills

1,100

360 incandescent lamps and appliances

360

10 are lamps

220

THE paper on Electricity in the Production of Aluminium," read by A. S. Brown before the American Institute of Electrical Engineers, and published in our last issue, was followed by the following discussion:-

Prof. FRANCIS B. CROCKER: There are two points in connection with aluminium which I wish to consider particularly. The first relates to the properties and the second to the production of aluminium. I think that Mr. Brown spoke very truly in regard to the exaggerated ideas of the advantages of aluminum, but I do not think that he went quite far enough. The popular idea of aluminium is that all of the good properties of its alloys are attributed to aluminium itself. It is like one individual having all the good qualities of all his relatives attributed to him personally. This is, of course, an absurd fallacy. Nevertheless, it is one that is made in every newspaper article on the subject, and I am sorry to say that it is frcquently made in technical journals. The most common mistake of the kind is to attribute to aluminium itself the tensile strength of aluminium bronze, which exceeds that of wrought iron, and is about as high as good specimens of steel. It is really one of the most tenacious metals known, but its composition is about nine parts of copper to one part of aluminium; yet its tensile strength is almost invariably attributed to pure aluminium, having a specific gravity of 2-6, which is only one-third that of iron. They take the low specific gravity of pure aluminium and the high tensile strength of aluminium bronze. As a matter of fact, the specific gravity of aluminium bronze is higher than that of iron. Therefore, we do not have lightness combined with high tensile strength., Turning again to aluminium itself, its tensile strength is about 26,000 lbs. per square inch; in other words, about one-third that of iron. This just balances the difference in specific gravity, but still leaves the advantage in favour

of iron, because one-third of the volume has the same strength and the same weight as a rod of aluminium. Now, the same exaggeration is applied to its other qualifications; for example, its chemical properties. Aluminium bronze is remarkably free from tarnishing. A bright surface of aluminium bronze may be exposed to the atmosphere for several months and retain its polish. That property is attributed to aluminium itself. Aluminium, as Mr. Brown said, is not particularly liable to corrosion, but if it is subjected to salt water or alkaline water, or even ordinary moist air, it does tarnish or oxidise rapidly. Salt water is quite hurtful to it. Therefore, freedom from oxidation is another property that is wrongly attributed to it; and the objection to all this is that it gives a very wrong impression in regard to what would otherwise be a good and legitimate object of admiration. I am not prejudiced against the metal aluminium, and would be very glad to see it used extensively, but I do not think its extensive use will be hastened-in fact, I feel quite sure it will be retarded-by absurd exaggerations of its good qualities, because when people do come to use it they will be greatly disappointed. This common idea, for example, that it has 100,000 lbs. tensile strength per square inch, and about one-third the specific gravity of iron would lead any one into serious difficulties. There are certain things that seem to have a glamour about them-a word which Mr. Brown uses, and which expresses the fact perfectly. Storage batteries and aluminium seem to be particularly favoured by the public, and it has occurred to me that a combination of aluminium and storage battery-that is an aluminum storage battery-would be simply irresistible. Now, taking seriatim the actual properties of the metal, and considering them as mechanical, chemical and electrical, we have under the mechanical head a specific gravity of about 26, which is almost exactly one-third that of iron, and its tensile strength is 27,800 lbs., according to Mr. Brown, which is again almost exactly one-third of ordinary wrought iron. Therefore, iron and aluminium have equal strength, weight for weight; but iron has, as I have said, the great advantage of one-third of the bulk for the same strength and weight. Furthermore, any metal which "can be easily cut with a knife" is not particularly good for structural purposes as a metal. In my opinion it is too soft altogether. It is very much such a metal as zine or tin. In fact, one can hardly tell the difference except by the weight, in filing or cutting it; and certainly tin or zinc are seldom used for structural purposes, and I do not think they would be, even if they were very much lighter than they are. Taking up the chemical properties-I have already alluded to the ease of oxidising, which, as I say, is not excessive, but still about equal to other metal, such as tin, zinc and iron. It is easily, in fact, eagerly, attacked by acids. It is not much affected by sulphur or sulphuretted hydrogen, which is a great advantage. It is very freely dissolved by alkalies, whereas most other common metals are not. In an ordinary alkaline solution, aluminium is dissolved, as most metals are, in acids, with the evolution of hydrogen. This is quite a serious disadvantage for a common metal, which is liable, for example, to have soap used upon it. We do not expect metals to be attacked by alkalies. As to the electrical properties of course conductivity is about the only one. The electrical conductivity is about twice that of copper of equal weight, and is about half that of copper of equal volume. Where it is important to have a light wire, and the size is not to be considered, you can use an aluminium wire, because you get an advantage of 2 to 1 in weight. But when you consider size, for instance, a wire which has to be covered with insulating material that is expensive, then you would have a disadvantage. The figures happen to be very simple in all these cases. In regard to the manufacture of the metal, that, I think, is an electrical monopoly, for the simple reason that I do not think anything else can successfully compete with electricity in the production of a metal the chemical affinities of which are as high as those of aluminium. Aluminium has great chemical affinities, ranking about half way between the ordinary metals and metals like sodium and potassium. These chemical affinities exhibit themselves when it is attempted to separate aluminium from chlorine or oxygen, for example. The ordinary smelting process does not seem to have ever been successful in the reduction of aluminium. So far as I know, aluminium has never been successfully reduced as iron or other ordinary metals are reduced by merely smelting in a furnace with coal. The nearest approach to this is smelting in presence of carbon, but with a very high temperature obtained by the electric current, higher than can be obtained by smelting. Therefore, even if we employ the process of smelting, we still have to employ electricity. In any electrolytic reduction of the metal, of course, we have to employ electricity. Such a process seems to be a very simple and effective method, i.c., the plain electrolysis of some compound of aluminium, the electrolyte being in a fused state between two electrodes. Now the fused state is necessary instead of the ordinary aqueous solution, because if you attempt to separate aluminium in an aqueous solution you will get hydrogen instead of aluminium. In other words, water is more easily decomposable than the aluminium compound. Then we have, as the only other likely substitute for these two clectrical processes, the ordinary chemical method of reducing, by means of metallic sodium, some compound such as the chloride or double chloride of aluminium and sodium. But even then I think we had better make our sodium by electricity; so it would still be an electrical process. So far as I can see, and exOperience in the past few years seems to corroborate this view, electricity is the only commercial means of producing aluminium at the present price. In the old days, when the chemical process was used, aluminium was $12 or $15 a pound. Now it is about $1, and I doubt if any chemical process could compete on this basis. Therefore, the reduction of aluminium seems to belong to electrical science, and it is certainly a very interesting and important application of electricity, and is, I think, destined to be perfectly successful.