2,185,000 horse-power, had been made by 1880. In every important industry in which water power is largely employed, a relatively greater amount of steam power was in use at the end of the decade than at its beginning. The causes which have led to this result form an interesting study in themselves, but their discussion will not be attempted in this paper.

MEETING 358.

The Bessemerizing of Copper Mattes.

BY DR. E. D. PETERS, JR.

The 358th meeting of the SOCIETY OF ARTS was held at the Institute on Thursday, February 24th, President Walker in the chair.

After the reading of the minutes of the previous meeting, the President introduced Dr. E. D. Peters, Jr., of Walpole, who spoke on the "Bessemerizing of Copper Mattes."

Dr. PETERS said: Despite the technicality of my subject, the process that I am about to describe has a claim to the attention of the general public as being a close counterpart of the steel Bessemer process which has so entirely revolutionized the iron industry.

But before you can at all appreciate the advantages possessed by this new method of treating copper ores, it is absolutely necessary that you should have a tolerably clear idea of the ordinary methods. in use all over the world.

[Here the speaker gave a brief description of the ordinary furnace processes used in smelting copper ores. following the metal to the stage of blister-copper, which is the same product as that derived from the Bessemerizing method.]

Having now some idea of the long and complicated operations required to produce metallic copper from its sulphide ores, you can better appreciate the rapidity and simplicity of the new method.

I will not go into the history of this invention. Many noted metallurgists have had a strong faith in the possibility of applying the

same process to copper mattes that has been so successful in the manufacture of steel, and some have approached a successful termination. But I think no candid person can dispute me when I say it was reserved for M. Pierre Manhès to make the Bessemerizing of copper mattes a metallurgical and commercial success in his works in France, whence it was brought to this country by the president of the Parrot Copper Company, and is yet successfully practiced in their works at Butte City, Montana. My own part in the matter was simply to build that portion of the smelting plant to treat the copper ores, and produce them in the shape of a matte (a fused sulphide of copper and iron) ready for the Bessemer process. This latter portion of the plant was built and conducted by pupils of M. Manhès, and I simply describe what I saw as a spectator.

The results of blowing a column of air through a vessel of molten iron are much simpler than when copper matte is substituted therefor. In the first instance we have a metal already ninety-five per cent fine or over, and containing only a few fractional percentages of impurities, such as C, Si, S, P, etc., most of which are also volatile. Therefore, little slag is formed, and when the operation is completed the volume of metal has sunk but little. But when air is blown through a copper matte of average grade, say thirty per cent, we have some seventy per cent of impurities to remove, one-half of which is iron and non-volatile. This encumbers the surface of the bath with enormous quantities of sticky, tenacious slag, consisting of subsilicate of iron, and when the blowing is finished we have left only some six hundred pounds of metallic copper, an amount too small to manipulate. [It should be understood that practical reasons have thus far limited a converter charge to two thousand pounds of matte.]

A still more important difference between iron and matte is that the latter is not a homogeneous substance; or rather does not remain so after the operation has proceeded so far as to oxidize all the iron and a portion of the sulphur present, so that the molten charge is a pure subsulphide of copper. It will be readily seen that as each additional particle of sulphur is volatilized, a particle of metallic copper is set free and sinks to the bottom of the converter, where it is met by the blast and so churned about and driven through the matte and slag that it is impossible to attain a clean metallic product.

This difficulty has been ingeniously conquered by M. Manhès by

placing the tuyères in a horizontal circle, two inches above the bottom of the converter, so that an opportunity is given for the metallic copper to collect in an undisturbed pool, below the influence of the blast, which still continues its oxidizing duties until the last particle of sulphide is decomposed, and the metal just reaches the level of the tuyères, when it is poured into moulds.

This horizontal placing of the tuyères was virtually the key to success, and after enumerating these few modifications there remains but little to describe to those familar with the genuine Bessemer process.

The difficulties arising when treating low-grade mattes, from the excessive formation of slag and the minute volume of the metallic product, are simply met by dividing the operation into two stages.

Assuming a twenty per cent matte to be under treatment; it is melted in a small cupola and run into the converter, where it is blown until its grade is increased to about sixty-five per cent, the slag being poured off once during the blowing, if it threatens to become trouble

some.

When the charge has become nearly a pure subsulphide of copper (sixty-five to seventy per cent), the converter is turned down, and its entire contents poured into a large iron kettle on wheels. The slag, which forms a cake on top, and contains one or two per cent of copper, makes a most welcome flux for the ore smelting, while the cone of rich matte is laid one side till 20 or 30 tons accumulate, when it is remelted in a cupola, again run into the converter, and blown till it becomes blister-copper,- ninety-six to ninety-nine per cent.

An ordinary "blow" takes from twenty to forty minutes, so that allowing for changes, delays, etc., 25 to 30 blows of 2000 pounds each are made in twenty-four hours.

The converters are, of course, very much smaller and lighter than those used in steel manufacture, which hold 6 to 10 tons, and are lined with crushed quartz, to which is added just sufficient plastic fire-clay to make it hold together. After putting in a bottom several inches thick, an ordinary oil barrel is placed erect upon it, and the mixture rammed about this pattern, thinning out to almost nothing at the throat.

A battery of converters consists of three, of which one is in use, one undergoing repairs, and the third drying, ready for use.

When the operation is divided into two stages, as explained above, five converters are found sufficient for the purpose.

When the product of the blowing is an enriched matte, no extraneous fuel is needed to keep the converter at the proper temperature; but in running for blister-copper, the vessel gradually cools, until after the third or fourth blow it is found necessary to throw some 25 pounds of coke into the empty converter, which, being burned by a light blast, soon restores the lost heat.

This is not the place to go into questions of comparative cost, but it is evident to the meanest capacity that a great saving in plant and a great simplifying of operations must arise from the adoption of such a short cut to metallic copper. On the other hand, a constant large supply of matte is necessary to keep the plant properly at work, and a staff of highly trained workmen must be kept under regular pay.

The most evident saving is that of fuel, so that the economy of the new process is most marked where the price of fuel is the highest.

Under present conditions, one would hardly think of adopting it where coal was cheap and good, though it is quite within the bounds of possibility that, by greatly enlarging the converters and substituting machinery for man power in the manipulation of the same, the improved Bessemer operation may eventually be found the most economical under all conditions.

Since the electrolytic methods for the treatment of argentiferous blister-copper have become commercially successful, the field for the introduction of M. Manhès invention has been considerably enlarged; for now it is feasible to adopt his method on silver and gold bearing copper ores, and, by concentrating the precious metals in the blister-copper, obtain a product that can be separated with economy, whereas formerly it was necessary to separate the silver from the copper while in the condition of a matte, thus producing residues that could not be treated by Bessemerizing.

Another advantage gained by the employment of this process is the more or less perfect elimination of arsenic and antimony from the matte treated. M. Manhès claims that the elimination of these metalloids is perfect, no matter how great their quantity; but without expressing any opinion on such a very strong claim, I can testify that a blister-copper absolutely free from arsenic, and of most excellent. quality, is produced without difficulty from matte containing enough

of these impurities to seriously impair the quality of the refined copper made from it by ordinary methods.

At pres

The future of the Bessemerizing process depends largely upon the policy of those who claim to control it in this country. ent, it is only used at the Parrot company's works in Montana; but we are informed that great improvements have been made, and it is probable that before long efforts will be made to introduce it at other points, where expensive fuel and low-grade sulphide ores demand something cheaper than the ordinary methods.

Prof. T. Egleston has published a paper in The Columbia College Quarterly Magazine, giving about all details that are yet known regarding the practical working of this process.

The meeting closed with a vote of thanks to the speaker.

MEETING 359.

Coal Mining.

BY MR. STUART M. BUCK.

The 359th meeting of the SOCIETY OF ARTS was held at the Institute on Thursday, March 10th, Mr. H. M. Howe in the chair.

After the reading of the minutes of the previous meeting, the chairman introduced Mr. Stuart M. Buck, of West Virginia, who read a paper on "Coal Mining; with a review of the more recent experiments on the action of dust in colliery explosions."

Mr. Buck first described the different kinds of coal, giving their chemical composition, physical properties, etc. He then took up the general system of working coal mines, illustrated by blackboard sketches. The entries to the mine are driven in pairs for the sake of ventilation, and they are usually from eight to twelve feet in width, and separated by pillars of solid coal about 30 feet thick. These pillars are broken through by narrow cross-cuts, at intervals of from 100 to 150 feet (the old break-throughs being closed as soon as new ones