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The dressing of these ores has been fully treated in the second volume of the Metallurgical Review.

The great bane of mining in Lake Superior is surface improvements. Many of the mines owe their want of prosperity or even their failure to this cause alone. Money which should have been put into the mine has been spent on the surface. The stockholders consequently often find themselves in serious difficulty, and sometimes with no workable mine and no capital. In most cases, if the surface improvements had been temporarily dispensed with, and the money spent in the mine, it would in time have paid for what was done at the surface. Lake Superior is not the only mining country where this has happened, but much of the failure charged to other causes is due to this alone. When, however, it is taken into consideration, that this country was settled as the result of wild speculation, that mines were opened without sufficient exploration, and then abandoned without any real development, and, in some instances, before it could be known whether there was value in the property or not, it is scarcely to be wondered at that capital did, for a time, shun Lake Superior altogether. Some of the best examples, however, both of mining and milling, as well as of management, can be found in the copper regions of Lake Superior. Very striking examples of the extremes, both of success and of failure, make marked contrasts with each other in different parts of the Lake. The half-ruined town of Rockland and the very quiet city of Ontonagon would hardly lead one to suspect their former activity and wealth, while the villages of Calumet and Red Jacket are notable examples of prosperity and of the enlightened and liberal policy of the directors of the Calumet & Hecla mines. There is nothing which foresight and an enlightened philanthropy could suggest but has been here carried into effect for the benefit of the mining population.

On the whole, Lake Superior cannot be said to be a prosperous mining country. Capital, which was tending towards it, was paralyzed by the panic of 1873, and some rude examples of want of capacity, or want of honesty, together with the fall in the price of copper from $0.26 in October, 1873, to $0.17, October, 1877,* have not tended to attract it there. The difficulty of the region does not lie in the want of copper, for there is an abundance of it, nor in mining, for, in general, it is skilfully done, but in the dressing. The following assays of tailings from the washers, yielding the different grades

* The price, while this article is passing through the press, is $0.15 to $0.15.

of copper, I made in the winter of 1875-6. The samples were taken from a mill whose ore yielded less than two per cent.

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Much of this copper is attached to small pieces of rock and is carried off with it. This has led to restamping the tails, as is done in the Calumet & Hecla; this produces other rich tails, and a large loss in float copper. If the price of copper should ever rise, or even if at the present time any one could or would take the time and make the experiments to solve this problem, he would be a benefactor to the country. Every one now is working in the same way; the type of one mill is the type of them all; they differ only in the intelligence of their management. A new element will have to be introduced before the losses decrease, and should the price of copper fall lower, or even remain as it is, the outlook for the country is gloomy.

In conclusion, I beg to express my thanks to the officers of the Allouez Mine, who have allowed me to publish a large amount of information gained in an official examination of that mine; to Captain Parnell, of the Phoenix, for great courtesy in giving information, both at the mine, and since by letter; and to Captain Robert, of the Atlantic Mine, for a rough sketch of the mine skip.

THE MECHANICAL WORK PERFORMED IN HEATING THE BLAST.

BY PROF. B. W. FRAZIER, LEHIGH UNIVERSITY, BETHLEHEM, PA.

(Read at the Wilkes-Barre Meeting, May, 1877.)

THIS interesting application of the laws of thermodynamics to metallurgical practice has not been discussed by any writer, within my reading, except the late Prof. Callon of Paris. In his Cours de Machines,* Prof. Callon has given a short but lucid discussion of this subject in the admirably clear style for which he was remarkable. Although the interest attached to the subject is rather theoretical than practical, I have thought that an attempt to explain the mechanical action exerted in the hot-blast oven might not be entirely devoid of utility, especially in the suggestions which it involves.

The statement, that the mechanical work performed in heating the blast is, when high temperatures are produced, considerably greater than the work performed by the blowing-engine, may seem incredible to many who are practically acquainted with the subject, appearing, as it does, to conflict with the results of their experience.

It is, nevertheless, literally true, and I shall attempt in this paper to prove it, and to explain why it has not rendered itself palpably manifest in practice.

Before proceeding to the mathematical demonstration, it will be well to recall to mind the definitions of some terms employed by writers in mechanics and thermodynamics.

The actual energy of a moving body, as defined by Rankine, is the work which it is capable of performing against a retarding resistance before being brought to rest, and is equal to the energy which must be exerted on the body to bring it from a state of rest to its actual velocity. The value of that quantity is the product of the weight of the body into the height from which it must fall to acquire its actual velocity.

Vol. I, chap. x, 24, p. 312.

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The intrinsic energy of a fluid, according to the same author, is the energy which it is capable of exerting against a piston, in changing from a given state as to temperature and volume to a state of total privation of heat and indefinite expansion. In the case of atmospheric air, which may be considered a perfect gas, the algebraic expression for this quantity is

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the intrinsic energy of the air.

Po the normal pressure of the atmosphere.

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Vo =

V。 the volume of a given weight of air, when its pressure and temperature are p。 and To respectively.

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the absolute temperature of melting ice.
= 273°.

In the Centigrade scale To

In the Fahrenheit scale T. 493.2°.

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Tthe absolute temperature of the air. The value of this may be obtained from t, the temperature as recorded by the thermometer, by adding to it the absolute temperature of the zero of the scale.

In the Centigrade scale the absolute temperature of the zero of the scale is the same as that of melting ice, i. e., 273°.

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In the Fahrenheit scale, the temperature of the zero of the scale is 32° less than that of melting ice.

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7 the ratio between the specific heat of air at constant pressure and that at constant volume. The numerical value of y is 1.408.

The relations between the volume, pressure, and absolute temperature of air are expressed by the following equations :

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In case the change in the conditions of the air be made without accession or loss of heat, the following equations permit the determination of the variation in any one of these quantities, when we know the corresponding variation in either of the others:

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If, during the change in the conditions of the air one of these quantities remains constant, the following equations express the relations existing between the others:

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In order to simplify the discussion, I shall make the following assumptions:

1st. The absolute temperature of the air drawn into the blowing cylinder is To, and its pressure is po

2d. The blast loses no heat during its compression and its passage from the blowing cylinder to the hot-blast oven.

3d. The back pressure before the tuyeres is equal to the atmospheric pressure, P.; that is, we will neglect the excess of pressure over that of the external atmosphere which always exists in the hearth of a blast furnace while the blast is on.

4th. We will neglect all losses of pressure due to the friction of the air in the pipes, also to bends, sudden changes of section and leaks in the pipes, as well as the loss of pressure corresponding to the amount which is absorbed in producing the velocity of flow of the air through the pipes.

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