half times, by weight, more gunpowder to produce the same effects, while the residue left by its combustion, and the action of the gases evolved upon the weapons, were not found to be appreciable.

The startling invention by SCHÖNBEIN, in 1846, of a process which converted cotton into a new compound possessing highly explosive properties, more generally known as gun-cotton, awakened a lively interest among the seekers after the long-courted substitute for gunpowder. In Germany, France, England, Austria, and in the United States, experiments were immediately instituted to ascertain its adaptability to military purposes. France, a special commission of inquiry was appointed, which for a period of six years pursued its investigations, manufac-. turing no less than five tons of gun-cotton, and applying it to the varied purposes of warfare: so that, apparently, no point connected with its proposed application seemed to have been left untouched.

In

In every country so many serious difficulties were found to exist against its adoption that, gradually, the efforts were relaxed, and finally abandoned, in all save Austria. Baron W. VON LENK, then a captain of Austrian artillery, applied himself to the removal of the obstacles which it presented, and to perfecting its method of manufacture, until success has so far crowned his attempts as to present the spectacle to the world at this time of thirty-six batteries of rifled artillery in the Austrian service fully equipped with gun-cotton ammunition.

At a recent meeting of the British Association at Cambridge, a committee appointed for the purpose laid before the meeting an elaborate report of the progress of the improvements made in Austria, to which additional interest was imparted by the presence of General VON LENK, under the permission of the Austrian Government, and fully authorized to furnish drawings and samples of his own gun-cotton, manufactured at the imperial factory at Hirtenberg. The specimens submitted were found to differ from gun-cotton as ordinarily made by their complete conversion into one uniform chemical compound, invariable in composition, and termed Tri-nitro-cellulose.

It has long been known that gun-cotton is prepared by the immersion of cotton fibre in a mixture of nitric and sulphuric acids, or in a mixture of powdered nitrate of potash and sulphuric acid; and to those acquainted with the details of the manipulation, and their want of uniformity, it is not a surprising matter to find a wide diversity in its chemical composition and resulting properties. This diversity arises from a variation in the strength of the acids employed, from the manner of mingling the acids, or the temperature the mixture attains, from the duration of the time of immersion, and from the more or less imperfect removal of the acids by repeated

washings in water. As each one of these causes possesses a wide range in diversity, a more or less imperfect transmutation of the elements of water and nitrogenization of the fibre must of necessity have resulted in as many varieties of gun-cotton as there have been attempts to make it.

To locate each variable cause of diversity at a proper fixed point, and to combine all the causes thus fixed in the preparation of gun-cotton, can alone insure uniformity in the resulting product. Every maker of gun-cotton for photographic purposes has encountered these difficulties; and it is only recently that they have been successfully overcome in that branch of the useful arts. The pertinacity and assiduity with which photographers have pursued their researches to find a variety of guncotton adapted to their specialty, has been followed by VON LENK, until the coveted substitute has finally been discovered by him, and proven to be admirably adapted to the purpose so constantly kept in view.

Knowing, as he did, the extent and results of the experiments in France, General VON LENK has displayed no inconsiderable degree of confidence in his ability to bring his attempts to a successful issue; and our regard for his efforts is further heightened by his success in devising rifled guns equally adapted to the use of gunpowder and the new agent. These guns, which now compose entire field-batteries in Austria, use the elongated projectile, the surface of which exhibits projecting ridges covered with malleable metal, which "take the grooves,' annulling windage, and insuring the rotation of the shot without injury to the bore. Experiments on a large scale have been conducted by the batteries attached to the Second Regiment of Austrian Artillery, near Wiener-Neustadt, in which one-half of the guns were charged with gunpowder, and the other with guncotton. The results obtained have satisfied the advocates of the latter that the time is not far distant when the supremacy of cotton will be claimed on other than commercial grounds.

General VON LENK has materially added to our first knowledge in the specialties concerning the preparation of gun-cotton. Thus: he causes the cotton to be thoroughly cleansed at the outset, and, using the strongest acids attainable, he completely saturates the fibre in the mixed acids; and then, to insure a perfect conversion, the cotton is steeped in a fresh mixture of acids for a period of forty-eight hours. In place of washing until the water exhibits no action upon vegetable blue, he subjects the cotton to a running stream of water for six or eight weeks, and finally immerses it in a solution of silicate of potash before drying. The agency of the latter is by no means demonstrated; but it is alleged that it retards the rapidity of com bustion and modifies its bursting effect.

The Hirtenberg gun-cotton cannot be distinguished at sight

from ordinary cotton, and even under the microscope no difference in the appearance of the fibres is discernible. ments are harsh to the touch, and crepitate when pressed between the two hands. It is unalterable in water, however long immersed, recovering its properties when dried, and is without odor or taste. A portion held between the thumb and finger, and drawn through the dry, closed hand, becomes highly electric, readily attracting and repelling light substances. It explodes at a temperature of 377° F., and, under a blow from a hammer on an anvil, scattering, without igniting, the portions not struck. If a quantity be placed on a small heap of gunpowder, it may be exploded without igniting the latter, or even in the palm of the hand without injury to the skin. A roll, grasped by one end, may be exploded without igniting the portion held in the hand. Exposed to a moist atmosphere, it is not permanently impaired, as is the case with gunpowder. Placed in a bell-glass over water, it absorbed only two and a half per cent. of moisture in forty-eight hours, and this, by subsequent exposure for a few minutes to the air, was dispelled, and the specimen recovered all its original properties. It does not dissolve in ether, or alcohol, or in a mixture of the two substances named, and is, therefore, useless for the preparation of collodion.

While the properties thus enumerated were to a great extent common to the early varieties of gun-cotton, uniformity among them seemed to many experimentalists so impracticable as to establish at the outset a belief that the difficulties presented could not be overcome. It is not a little remarkable that whatever degree of uniformity was insured in the proportions of guncotton, made in our first experiments, it was found to be confined to those which it was most desirable to avoid. Among these was the evolution of gases arising from its combustion, which were innocuous to respiration and corrosive in their action upon the metal of the arms wherein it was employed, and the self-decomposition which the cotton underwent in time, despite all the efforts made to prevent it.

The new Hirtenberg gun-cotton has been subjected to a careful analysis by Lieutenant Von Karolyi, who, after an explosion by an electric wire, in an exhausted ten-inch shell (under circumstances analogous to those which attend its explosion in firearms), collected the products, and they were found to consist of

A glance at these constituents will show that, while many of

them are combustible, as in the case of the combustion of gunpowder, they are not deleterious under the circumstances which attend their evolution, and they are further characterized by the absence of the vapors of nitrous and hyponitric acids, of a residual solid deposit, and of a cloud of smoke to impede the sight of a soldier or betray his position. After forty rounds of Hirtenberg cotton were fired from a steel rifle barrel, the bore of the latter was left bright and polished as the surface of a mirror.

The self-decomposing influences to which the early varieties of gun-cotton were subject are not found to exist in the Hirtenberg product. Specimens made in the years 1856, 1860, and 1862 have been subjected to a careful chemical analysis, and they presented no greater diversity than is found to arise whenever the same material is submitted to a quantitative analysis. A parcel of General Lenk's cotton, after lying for weeks in a pond, was deposited a long time in a running stream of water, and then exposed for a month to the air, subject to all the various influences of dew, rain, and sun, night and day, without its original explosive qualities being in the least degree impaired.

The same is true for specimens which have been stored for twelve years in the magazines in Austria; while the Austrians themselves recognize to-day in gun-cotton a substitute for gunpowder, possessing many great advantages which the latter, from its nature, can never possess.

I cannot close this paper without expressing my abiding conviction that the coveted substitute for gunpowder will yet be found in gun-cotton. If the same spirit for improvement and determination to adapt it to war-purposes be followed which photographers have displayed in forcing it to supply to them a vehicle for the production of sun-pictures, gunpowder will yet bear the same relation to gun-cotton that the old metallic daguerreotype now holds in relation to the "cartes de visite" of the present day. For half a century the application of steam to locomotion was impeded by unbelievers; for years phosphorus was pursued to supplant the tinder-box in the production of light; for years the sewing-machine was resisted as a visionary undertaking; and not until recently has the supremacy of the percussion lock over the old flint been universally acknowledged.

It is true that some of these improvements are mechanical, and tangible things which involve but little familiarity with the origin and composition of the materials; but let the same number of minds and hands operate on gun-cotton as have been engaged in bringing to a successful termination the experiments on coal oil and coal-oil lamps, or manufacturing candles from lard, both of which substances have existed since the days of Adam, and the utility of which, for illumination, dates back scarce twenty years, and further attempts to improve gunpowder or furnish a substitute will be regarded as needless an undertaking as an tempt would now be to improve a friction match.

A METHOD OF DETERMINING A PLANE OF DEFILEMENT.

BY LIEUTENANT JAMES R. WILLETT,

(38th Regiment, Illinois Infantry, Engineer Department, Nashville, Tennessee).

THE following method was the result of necessity; and there is nothing contained in the following article but what I have applied in practice. It is believed to be original, and is certainly so, as far as my knowledge extends.

Having found this method to give accurate and in every way satisfactory results, and easy in its practical application, it is now submitted, in the hope that it may prove useful to officers engaged on engineering duty.

Let it be desired to construct a fortification at a given point F, and to defile it from the hills in front, H', H2, H3, H1, H3, Ho, H', and H8.

Find the courses to the hills, and the vertical angles to their summits; plat the courses, and on them mark the points P1, P2, P3, P4, P5, P6, P', and Ps, where the lines from the point F to the several summits would pierce a horizontal plane taken at any assumed distance above the point F; then the points P1, P2, P3, P, P5, P6, P', and Ps will all be of the same elevation, they being situated in the same horizontal plane.

The plane passing through any two of these points P1, P2, &c., and also the point F, will be the rampant plane of those points and the point F; and, further, the plane that passes through any