inferior iron for this purpose, and its employment inevitably led to a loss of character in the structure, and danger to the public.

CRYSTALLINE STRUCTURE OF IRON INDUCED BY VIBRATION.

The spontaneous change forged and rolled iron undergoes when submitted to continuous vibration, is productive of so much critical danger, especially in the case of railway machinery, that an investigation into the best means of remedying the resulting evils has been viewed as an engineering question of vital importance. Among others, Mr. Schimmelbuch, of Liege, has undertaken the subject, and the following is an epitome of his investigations: A bar of pure unalloyed iron was struck by a hammer three times in a minute for six consecutive weeks; at the expiration of this time it broke into three pieces. Before the experiment the bar was a good specimen of fibrous iron; after, on the contrary, its fracture exhibited a brilliant crystallized structure, resembling that of antimony.

A bar of iron alloyed with nickel, submitted to the same treatment, underwent no change.

A very simple means exists of recognizing this changed condition of iron, so dangerous in its consequences. Pure iron, when magnetized by contact, loses its magnetic properties immediately the needle is detached. On the other hand, iron combined with minute quantities of some foreign body, such as carbon, oxygen, sulphur or phosphorus, remains magnetized. The efficacy of this simple test has been established by repeated experiments.-London Photographic

News.

Under the patronage of the Austrian government M. Bourville has also recently instituted a course of experiments with a view of throwing some additional light on the subject of the induction of a crystalline structure in wrought iron through vibrations.

M. Bourville's apparatus consisted of a bent axle, which was firmly fixed up to the elbow in timber, and which was subjected to torsion by means of a cog-wheel connected with the end of the horizontal part. At each turn the angle of torsion was twenty-four degrees. A shock was produced each time that the bar left one tenth to be raised by the next. Seven axles were submitted to the trial. In the first the movement lasted one hour, 10,800 revolutions, and 32,400 shocks being produced; the axle, two and six-tenths inches in diameter, was taken from the machine and broken by a hydraulic press, and no change in the texture of the iron was visible. In the second, a new axle, having been tried four hours, sustained 129,000 torsions, and was afterward broken by means of a hydraulic press; no alteration of the iron could be discovered by the naked eye on the surface of rupture, but, tried with a microscope, the fibres appeared without adhesion, like a bundle of needles.

A third axle was subjected, during twelve hours, to 338,000 torsions, and broken in two; a change in its texture and an increased size in the grain of the iron were observed by the naked eye. In the fourth, after one hundred and twenty hours, and 2,588,000 torsions, the axle was broken in many places; a considerable change in its texture was apparent, which was more striking toward the centre,

and the size of the grains diminished toward the extremities. In the fifth, an axle submitted to 23,328,000 torsions, during seven hundred and twenty hours, was completely changed in its texture; the fracture in the middle was crystalline, but not very scaly. In the sixth, after ten months, during which the axle was submitted to 78,732,000 torsions and shocks, fracture produced by a hydraulic press showed clearly an absolute transformation of the structure of the iron; the surface of rupture was scaly, like pewter. In the seventh and final case, an axle submitted to 128,304,000 torsions presented a surface of rupture like that in the preceding experiment; the crystals were found to be perfectly well defined, the iron having lost every appearance of wrought iron.

PROPERTIES OF A MIXTURE OF CAST-IRON AND NICKEL.

Meteoric iron, as well known, is the most ductile of all varieties of iron, and it is recorded by travellers that the Esquimaux have instruments made from it so ductile that they may be made to bend round the arm. All meteoric iron contains a small percentage of metallic nickel, and it has been suggested by chemists that by mixing iron and nickel artificially, an alloy of iron as strong and ductile as meteoric iron would be obtained. With a view of testing this theory, and with a hope of obtaining a metal of great tenacity, suitable for the casting of cannon and heavy ordnance, Mr. Fairbairn, the celebrated English engineer, has recently instituted a series of very carefully conducted experiments of mixing a certain proportion of nickel with cast iron. The result, however, has failed entirely to realize expectation, inasmuch as the ingots prepared were found to have less than one-half the power to resist impact that similar ingots of pure iron possessed.

"It is uncertain what might have been the results had the castings produced been treated as cast steel, and hammered out until they were rendered malleable and magnetic. This process was not, however, attempted, as, judging from the appearance of the fracture, they were more likely to crumble under the hammer than attain malleability."

In a report on the above subject to the Manchester Philosophical Society, Mr. Fairbairn says in conclusion, "During the last two years, innumerable experiments have been made to produce a metal of increased tenacity suitable for the construction of heavy ordnance; but the ultimate result appears to be, that there is no metal so well calculated to resist the explosion of gunpowder as a perfectly homogeneous mass of the best and purest cast iron, freed from sulphur and phosphorus."

COMPARATIVE STRENGTH OF COLD-ROLLED

ROLLED IRON.

AND HOT

The following is the result of a series of experiments recently instituted by Mr. Fairbairn, the celebrated English engineer, upon the tensile strength of bars of wrought iron, rolled cold or hot:

"The first experiment was on a bar of wrought iron, in the condition in which it is received from the manufacturer (black). The diameter of the piece experimented upon was 1.07 in.; its area, 0.85873 square inch. The laying on of a weight of 46,426 lbs. produced an elongation

on a length of 10 ins. to the extent of 1.30 in.; and the laying on of 50,346 lbs. produced an elongation of 2.00, with a breaking weight per square inch of, in pounds, 58,628, and in tons, 26.173. The diameter at the point of fracture, after this experiment, was 0.88 in. The second experiment was on a bar similar to the preceding, but rolled cold. Diameter, 1.00 in.; area, 0.7854 square inch. With a weight of 64,255 lbs. laid on, it elongated rapidly, and the breaking weight was per square inch, in pounds, 81,812, and in tons, 36.523. The third experiment was also on a bar of iron rolled cold, with a diameter and area similar to the foregoing. The elongation of a length of 10 ins. was, in inches, 0.6, when a weight of 62,545 lbs. was laid on. With 69,295 lbs. laid on, the elongation was 0.79 in., and the breaking weight per square inch 88,230 lbs., in tons 39.388. The diameter after fracture was 0.85. The fourth experiment was on a bar of similar iron to the preceding, turned in a lathe. Diameter and area same as in the two foregoing. With a weight laid on of 30,910 lbs. the elongation was 0.15, and 2.20 with a weight of 47,710 lbs. Here the breaking weight per square inch was, in pounds, 60,746, in tons, 27.119. The diameter after fracture was 0.80. Thus it will be seen, that in an untouched or black bar the breaking weight was 50,346 lbs.; per square inch 58,628 lbs., or 26.173 tons strength, the untouched bar being unity, 1.000. That the breaking weight of a bar rolled cold was 69,295 lbs. ; per square inch 88,230 lbs., or 39.388 in tons strength, the untouched bar being unity, 1.505. The breaking weight of a turned bar was 47,710 lbs.; the breaking weight per square inch 60,746 lbs., or 27.119 in tons strength, the untouched bar being unity, 1.006. From this it is evident that the effect of consolidation by the process of cold rolling is to increase the tensile powers of resistance from 26.17 tons per square inch to 39.38 tons, being in the ratio of 1: 1.5, one half increase of strength gained by the new process of cold rolling. When, however, the iron rolled cold has repassed through the fire, many of the pores before consolidated must again be opened, there arising a consequent diminution of the strength previously gained. Experiments made at Woolwich on the metal of a monster wrought-iron gun showed a strength of 50,624 lbs. in the direction of the grain, but of only 43,339 lbs. when strained across the grain."-London Engineer.

From a paper recently read before the Liverpool Architectural Society, by Mr. Wm. Stubbs, we derive the following useful memoranda:

The first point to be ascertained by an architect with a casting of iron is to find out what it has to do. The practical man wants simple tools. Science is always consistent with successful practice, therefore simple rules are sufficient. The following for iron pipes of ordinary sizes answers well, and it never has been published before. It is based upon the fact that a 10-inch pipe one inch thick will stand the pressure of 100 yards head of water. The coincidence of one inch of metal to every 10-inch diameter and 100 yards pressure should be remembered. For every inch in the diameter of pipe, increase or deduct

one-tenth of an inch, and for every yard of pressure increase or deduct one-hundredth of an inch.

In calculating the strength of columns great care is necessary. The safe plan is to find the diameter of a solid column necessary to bear the compression, and then distribute the same area of metal in tube form as a hollow column. A solid column 10 feet long, and having an area of 10 square inches (good metal), will bear 10 tons pressure. This rule can be conveniently carried out, and it is safe and practical.

EXPERIMENTS WITH WIRE ROPE.

Some experiments, important to all persons engaged in the manufacture of wire ropes, or who may be accustomed to use them, have just been made by Mr. J. Daglish, who has communicated the results to the North of England Institute of Mining Engineers. The conclusions arrived at were, that half the strength of the rope was lost by heating the wire; that the ordinary joint is much weaker than any other portion of the rope; that if a flat rope was well spliced it was not weakened thereby, but if the workmanship was bad, it lost from twenty-five to thirty-three per cent. of its strength. In either event, a round wire rope spliced became thirteen per cent. weaker than before. Round steel-wire rope will bear more than double the weight required to break iron-wire rope of similar diameter.

PROTECTION OF IRON AND STEEL.

Professor Vogel recommends, for the protection of iron and steel tools against rust, a solution of white wax in benzine. Moderately heated benzine dissolves half its weight of wax; and if this solution be carefully applied to the tool with a brush, the evaporation leaves a very adhesive and permanent coating of wax, which will preserve the metal even from the action of acid vapors. — Dingler's Polytechnisches Blatt.

AMERICAN ZINC.

At Bethlehem, Pa., about thirty tons of metallic zinc are now produced weekly from the ore yielded by the mines of the Lehigh Zinc Co., and when the furnaces are all in operation the production will be increased to two thousand tons per annum. All the articles required in the manufacture of the zinc are made upon the premises, as retorts, muffels, fire-bricks, etc., of ingredients brought from the surrounding country, no foreign material being used. This zinc is claimed to be equal to the best distilled zinc sold by manufacturing chemists.

Heretofore, we think, metallic zinc has not been produced in quantity in the United States.

SHEET ZINC FOR ROOFING.

A report of a committee appointed by the Central Society of Architects, in Paris, recommends "that zinc, which was at first rejected, but is now so generally used, should be applied with great

care, as certain precautions, very simple, but never to be overlooked, are indispensable. Thus, contact with plaster, which contains a destructive salt, is to be avoided; also, contact with iron, which is very injurious, and liable to cause a rapid oxidation. Eave-gutters should always be supported by galvanized brackets, and no gutter or sheet zinc should be laid on oak boards."

ON ETCHING.

The London Builder furnishes the following practical notes on the subject of "etching," with a view of especially commending the work to amateurs in ornamentation.

First, as regards copper plates,—which in many respects have an advantage over steel for the use of amateurs, - procure a thin plate, properly polished on the surface, at any of the regularly-established coppersmiths. These can be had of the size of several feet down to a few inches. The surface of the plate being bright and free from tarnish, remove all grease with great care by washing with spirits of turpentine and then rubbing with very fine whitening and washleather. Care must be taken not to scratch the plate.

Having got rid of all grease, fix a hand-vice to one corner or some other convenient part of the plate; it is then ready for the reception of the etching-ground-a preparation chiefly composed of asphaltum, pitch, and virgin wax; there is, however, a great art in making this sufficiently plastic, so as to admit of its being properly spread upon the plate when heated. It is better, for ordinary purposes, to purchase it at the coppersmith's or tool-shop, where a supply can be had for about one shilling. A dabber, for the purpose of laying the ground on the plate, is also necessary. This is of a mushroom shape, and composed outwardly of very fine silk or kid leather, free from grease; the inside is padded with wool. This can be readily made by any person who has seen one of them. In order to prevent any grit or impurity which may chance to be in the etching-ground, it is better to tie it in silk. For the purpose of heating the plate, a hot iron, or a spirit lamp, placed below an iron frame on which the plate may rest, or other contrivance, may be used. Care is to be taken to make as little dust as possible. The metal must not be allowed to get too hot, for that would burn the etching-ground, and prevent it from sufficiently resisting the acid. The plate being of a proper heat, by drawing the etching-ground over the face a small quantity may be lodged upon it. This in the first instance is uneven; but may be spread in a flat, thin, even manner. Every part must be covered by the ground, or else the acid would leave such places as are bare liable to be corroded into holes. The ground, when this is spread on the surface, is of a light brown color, so delicate that it is difficult to see any pencil outline which might be transferred, or properly to see the scratches made by the etching-needle. In order to darken this, it is necessary, while the plate and etching-ground are still warm, to smoke it by the flame of a wax taper or candle. The flame must be kept moving about, and not allowed to touch the plate so closely as to burn the ground.

These operations, although simple, require some little practice and