Page images
PDF
EPUB

similar) still inculcate the necessity of adopting some effective process of deoxidation.

Before adverting to the experiments, it will be necessary briefly to state the opinions of several manufacturers, to whom the ores were submitted for inspection, and to whose sound practical views the country is indebted for many valuable improvements in the chemical as well as the mechanical process of the art.

To the iron-maker and engineer, a minute chemical analysis is of less importance than a knowledge of the methods used in the treatment of similar ores, derived from experimental and practical research. It is true, that none of the iron ores of this country will bear a comparison, in point of richness, with those of Turkey, excepting, probably, the red ores of Lancashire and Cumberland, which, although varying in their chemical compounds, are in other respects comparative, and exhibit (with the exception of the magnetic properties) characteristics of a very similar description.

According to Dr. Colquhon, of Glasgow, the Ulverstone ore contains

[blocks in formation]

This, by calculation, would give an average of 62 per cent. of iron, of nearly the same degree of richness as the ores of Samakoff, which, from Mr. Watson's analysis, yields 63.72.

Dr. Colquhon, in his inquiry into Mr. Clay's new process for making malleable iron direct from the ore, states, "that the red ores of Lancashire and Cumberland (which are a species of hæmatite) are exceedingly pure," and from an average sample, made up with great care, he found its constituents composed "of 63 per cent. of iron, 8 per cent. of earthy matter, and minute quantities only of lime and magnesia." In other respects the ores were entirely free from phosphorus, arsenic, and sulphur.

From this statement it is obvious that the Ulverstone ores, operated upon by Dr. Colquhon, do not widely differ from those analyzed by Mr. Watson; and viewing their other properties, they may be considered to approximate, irrespective of the quantity of metal produced

in each.

Concerning the other iron ores of this country, unfortunately none of them are analogous to those of Turkey, either as regards their chemical constituents, or the process by which they are reduced. It is the opinon of all the practical iron masters who have been consulted, that in smelting, the latter would require a different treatment VOL. X. 3RD SERIES-No. 3.-SEPTEMBER, 1845.

17

from that pursued with the ores of this country; but in making malleable iron, they are all agreed as to its fitness for Mr. Clay's new process, and that large quantities of the finest quality might be made direct from the ore, at a moderate rate of charge.

On these points there is but one opinion, but the manufacturers are somewhat startled at the idea of a new process of preparation; the smelting being considered a work of difficulty, from the expense and trouble which must be incurred, before the preparatory process of roasting can be accomplished. In fact, these opinions would infer that the whole must be looked upon, for some time to come, as an experiment, and that more particularly as the material to be worked upon is entirely new, and may present features of an exceedingly obdurate and refractory character. To a certain extent these views may be correct, as an excess of silex might prove exceedingly troublesome, and even with every care in the process of smelting, instead of a carburet, (by which the melting pigs of this country are so well known, and so justly appreciated,) a silicate of iron might be the result. It is true, that a flux of lime and a certain proportion of aluminous clay might remove, or in a great degree neutralize, the effects: but that can only be determined by experiment, and with such obstacles in advance, it will be necessary to guard against them, and to arrange future operations with a view to their removal.

But supposing them to be overcome either by this, or by the cleansing process already alluded to, or by such other means as may be deemed expedient, it is then to be considered how the minute particles of the ore are to be retained in the furnace, during the application of a strong and intense blast. It is clear that some process of calcination must be adopted, in order, not only to deprive the ore of part of its oxygen in the first instance, but to effect its carburation, and to hold it together until it is fused. For these objects the following experiments were entered upon, under the directions of Mr. Clay and Mr. Hague.

The first operation was to convert one of the cupola furnaces (4 feet diameter) at the Canal Street Works, Manchester, into a blast furnace; this was effected by lining it with fire-bricks to a height of 15 feet, leaving a hearth of 18 inches square, and 18 inches deep; it was made 2 feet 6 inches diameter at the boshes, and tapered to 18 inches at the top; with this furnace, and a moderately good fan blast, the experiments were made.

Previous to making the experiments at Manchester, Mr. Hague had tried the ores in various ways, and had subjected them to analysis and experiment. The first was made with only

oz. of iron ore,

oz. of chalk,

4

4

3

oz. of bottle glass,

oz. of charcoal,

oz. of clay.

12 oz.

which, having been deoxidized in a close vessel, and melted in the

crucible, produced a super-carburet of good No. 1 pig iron, and which worked freely under the chisel and file.

The next experiment was on a larger scale, and consisted of

30 lbs. of iron ore,

10 lbs. of bottle glass,

8 lbs. of clay.

48 lbs.

This, after being roasted, was pulverized, and mixed with water; it was then formed into bricks, and subsequently melted, with a limestone flux, in the cupola, by a fan blast, and produced a hard white iron, of a quality varying between No. 3 and No. 4 pigs.

The last experiment was repeated, with the addition of 2 lbs. of clay and 2 lbs. of common salt; 10 lbs. of scoria from the last melting being substituted for the bottle glass. The produce of this mixture was a white No. 3 iron, nearly the same as the last.

Other tests of a similar kind were made, with nearly the same success, but no change of any moment occurred in the quality of the iron, until experiments on a more extended scale were adopted. These are given in the words of the experimenter.

To be Continued.

An Account of the cause of the Colors in Precious Opal. By SIR DAVID BREWSTER.

This gem is intersected in all directions with colorific planes, exhibiting the most brilliant colors of all kinds. The cause of these colors has never, we believe, been carefully studied. Mineralogists, indeed, have said that they are the colors of thin plates of air occupying fissures or cracks in the stone; but this is a mere assumption, disproved by the fact that no such fissures have ever been found during the processes of cutting out, grinding, and polishing, which the opal undergoes in the hands of the lapidary. In submitting to a powerful microscope specimens of precious opal, and comparing the phenomena with those of hydrophanous opal, Sir David Brewster found that the colorific planes or patches consist of minute pores or vacuities arranged in parallel lines, and that various such planes are placed close to each other, so as to occupy a space with three dimensions. These pores sometimes exhibit a crystalline arrangement, like the lines in sapphire, calcareous spar, and other bodies, and have doubtless been produced during the conversion of the quartz into opal by heat under the peculiar circumstances of its formation. In some specimens of common opal the striature is such as would be produced by a kneading of crystallized quartz when in a state of paste. The different colors produced by these pores arise from their different magnitude or thickness, and the colors are generally arranged in parallel bands, and vary with the varying obliquities at which they are

seen.

Athenæum.

Experiments with Iron Targets at the Arsenal, Woolwich. The following experiments were undertaken lately, to determine the effect of shot upon the hull of an iron vessel, and also with the view of providing means for stopping the passage of water through a shot-hole near the water line. This latter object is sought to be effected by packings of various kinds fixed behind the sheathingplates, which by their elasticity will close over the hole after the passage of the shot through them.

The gun used in these experiments is a 32 pounder, placed at the distance of 30 yards from the target, and was loaded with the full charge of 10 lbs. of powder, and also with 2 lbs. and 1 lb. to produce the effect of a spent shot.

The initial velocity of the ball with the full charge is about 1800 feet per second, and with a 2 lbs. charge, 1000 ft. The diameter of the shot is 6 inches.

Target No. 1 is made of three thicknesses of 4 inch plates rivetted together by double rows of rivets arranged in rectangles of 24 inches x 14 inches. A shot fired through this with the full charge made a clean hole of its own diameter, with very little tearing or raising of the edges, and no rivet head started near the hole. The round piece cut out by the shot is broken into angular splinters of one, two, or three inches long, which diverge from the hole in all directions and with great violence. When the full charge is used no disturbance in the plate or the rivets round the hole is observable.

This target was not stiffened with angle-irons.

No lining is placed behind this target.

Target No. 2 is formed of single inch plates, flush jointed, singlerivetted, with frames 9 inches deep attached by double angle iron 6 x 3 inches. The frames are 33 inches apart.

One half of this target is lined at the back with pure India-rubber, and the other half with a mixture of India-rubber and cork-dust, containing 25 per cent. of the latter by weight; it is 12 inches thick. These linings are held to the sheathing by 1 inch screw-bolts with square heads outside, and nuts with washers of inch plate, & inches square inside, the washers completely covering the elastic lining. The bolts are in the centre of each square, or 8 inches apart.

Through the India-rubber and cork-dust, five shots were fired, all striking as was intended between the heads of the bolts. Two shots with the 10 lb. charge made clean perforations through the outer plate and passed through the lining without shattering it much, but each shot knocking off four or five of the back plates with great violence. The splinters from the outside plate all passed through the lining and radiated as before mentioned. After the passage of the shot, the elastic lining closed completely over the hole, so as to become impervious to light and apparently to water.

Several proportions of India-rubber to cork-dust have been tried, but the proportion before mentioned is considered the best. Three other shots were fired through this lining with the 2 lb. charge of powder, and were purposely made to strike within a circle of 12

inches diameter, so that the three holes joined; still the lining closed over the holes so as to exclude light, or prevent the passage of a thin walking-stick through it in any direction, which was considered very satisfactory. Of course, a great many of the back plates, about eight, were torn off.

With the small charge of powder the sheathing-plate suffers much more than with the full charge, the plate being considerably drawn into the hole, raising the edge inside, and stripping off the rivet heads near it. A shot fired with one pound of powder produced this effect in a greater degree, but in all cases the ball seems to carry with it a part of the outside plate torn from the hole, the piece increasing in size with the velocity of the cannon ball.

During an experiment with this target on the 3d June, a splinter struck a sentinel on duty at about 200 yards distance, passing entirely through the calf of his leg. It was a flat piece about the size of a penny, and must have glanced from the target at a very obtuse angle, and returned by the resistance of the atmosphere to where the man was standing, which was some way in advance of the horizontal line of the target.

A weak shot was passed through the lining of solid India-rubber, (12 inches thick,) which completely closed over the hole, apparently excluding the passage of water, and even air. This shot caused a great dislocation of the plates at the back, a number of which were driven off by the breaking of the nuts, consequent on the pressure thrown upon them by the tenacity of the India-rubber. The targets are 6 feet square.

Target No. 3 is formed of double inch plates rivetted together, and no frames. Half of this target is lined with solid India-rubber 8 inches thick, and held on by screw bolts and square washers as before. One chief objection to India-rubber as a lining for ships is its great expense. It would be also difficult to confine it in warm climates, as it assumes a kind of semi fluid motion when acted on by its own gravitation. The other half of this target is lined with a mixture of India-rubber and cork-dust, 12 inches thick, held on as before. In this case the cork-dust (which is cork chopped very fine) was in too large a proportion for the India-rubber, and consequently the hole formed by the shot did not close, and the lining itself was very much shattered.

Target No. 5 is formed of two plates, having a space of 10 inches between them, half of this space being filled in with felt, and half with India-rubber and cork-dust introduced in small pieces through hand-holes cut in the ceiling-plate between the frames, (which are 15 inches apart.) The outer sheathing-plate is inch thick, and the inner inch. The felt proved of no use in stopping the hole, and by its pressure it tore away a large portion of the ceiling-plate, about two square feet, where the ball passed through. This large piece was quite detached from the plate in various fragments which seem to have broken off quite short. A similar effect was produced in the ceiling-plate by the passage of the ball through the lining of Indiarubber and cork-dust, and the latter from being introduced in small

« PreviousContinue »