tance y, and the force in the first orbit at the same

ບ

Cor. 3. If instead of (1), be supposed=force

R

in the first orbit at the distance r, it will easily appear that the compound force in the other orbit, at G2 F2 v2 p2

the distance y, will = +

Ry

the same expression that is found after a very diffe

rent manner, PRINCIP. book 1st, sect. 9th.

109

Observations on Iron and Steel.

BY JOSEPH COLLIER.

READ NOVEMBER 18TH, 1796.

After examining the works of different authors, who have written on the subject of making iron and steel, I am persuaded that the accounts given by them of the necessary processes and operations are extremely imperfect. Chemists have examined and described the various compound minerals containing iron with great accuracy, but have been less attentive to their reduction. This observation more particularly applies to steel, of the making of which I have not seen any correct account.

It is singular to observe, how very imperfectly the cementation of iron has been described by men of great eminence in the science of chemistry. Cit. Fourcroy states the length of time necessary for the cementation of iron to be about twelve hours; but it is difficult to discover whether he alludes to cast or to bar steel: for he says, that short bars of iron are to be put into an earthen box with a cement, and closed up. Now steel is made from bars of iron of the usual length and thickness; but cast steel is made according to the process described by Cit. Fourcroy, with this essential difference: the operation is begun upon bar steel and not bar iron.

Mr. Nicholson is equally unfortunate in the account given in his Chemical Dictionary. He says, that the usual time required for the, cementation of iron is from six to ten hours, and cautions us against continuing the cementation too long; whereas the operation, from the beginning to the end, requires sixteen days at least. In other parts of the operation he is equally defective, confounding the making of bar with that of cast steel, and not fully describing either. In speaking of the uses of steel, or rather of what constitutes its superiority, Mr. Nicholson is also deficient. He observes, that " its most useful and advantageous property is that of becoming extremely hard when plunged into water." He has here forgotten every thing respecting the temper, and tempering of steel instruments, of which however he takes some notice in the same page.

Plunging into water" requires a little explanation: for if very hot steel be immersed in cold water without great caution, it will crack, nay, sometimes break to pieces. It is however necessary to be done, in order to prevent the steel from growing soft, and returning to the state of malleable iron; for, were it permitted to cool in the open air, the carbon which it holds in combination would be dissipated.*

*It is the opinion of some metallurgists, that a partial abstraction of oxygen takes place, by plunging hot metal into cold water.

I shall, at present, confine my remarks to the operations performed on iron in Sheffield and its neighbourhood: from whence various communications have been transmitted to me by resident friends, and where I have myself seen the operations repeatedly performed.

The iron made in that part of Yorkshire is procured from ores found in the neighbourhood, which are of the argillaceous kind, but intermixed with a large proportion of foreign matter. These however are frequently combined with richer ores from Cumberland and other places. The ore is first roasted with cinders for three days in the open air, in order to expel the sulphureous or arsenical parts, and afterwards taken to the furnaces: some of which are constructed so that their internal cavity has the form of two four-sided pyramids joined base to base; but those most commonly used are of a conical form, from forty to fifty feet high. The furnace is charged at the top with equal parts of coalcinder and lime-stone. The lime-stone acts as a flux, at the same time that it supplies a sufficient quantity of earthy matter to be converted into scoriæ, which are necessary to defend the reduced metal from calcination, when it comes near the lower part of the furnace. The fire is lighted at the bottom; and the heat is excited by means of two pair of large bellows blowing alternately. The quantity of air generally thrown into the furnace is from a

thousand to twelve hundred square feet in a minute. The air passes through a pipe, the diameter of which is from two inches and a quarter, to two and three quarters, wide. The compression of air which is necessary is equal to a column of water four feet and half high. The ore melts as it passes through the fire and is collected at the bottom, where it is maintained in a liquid state. The slagg, which falls down with the fused metal, is let off, by means of an opening in the side of the furnace, at the discretion of the workmen.

When a sufficient quantity of regulus, or imperfectly reduced metal, is accumulated at the bottom of the furnace (which usually happens every eight hours), it is let off into moulds; to form it for the purposes intended, such as cannon or pig iron.

Crude iron is distinguished into white, black, and grey. The white is the least reduced, and more brittle than the other two. The black is that with which a large quantity of fuel has been used; and the grey is that which has been reduced with a sufficient quantity of fuel, of which it contains a part in solution.

The operation of refining crude iron consists in burning the combustible matter which it holds in solution; at the same time that the remaining iron is more perfectly reduced, and acquires a fibrous texFor this purpose, the pigs of cast iron are taken to the forge; where they are first put into what

ture.