Pyroxylin or Gun Cotton. It has been about five years, I think, since the distinguished German chemist, Schonbein, made known to the world his discovery, that the action of a certain combination ot acids converted cotton and other ligneous fibre into a substance possessing explosive qualities of a highly interesting character. This discovery elicited much observation for several months. Numerous trials of its qualities were made in Europe and America, and among the results arrived at were, that it possessed thrice the projectile strength of gunpowder,—its combustion attended by a scarcely appreciable amount of smoke, that it may be kept any length of time without change, and that it is not permanently injured by becoming moist. These most important qualities would have secured it at once a permanent victory over all rivals, but for certain objectioiis which were deemed so serious as to cause its total abandonment as a substititute for gunpowder. These may be summed up under the following general heads:—1st, Its expensiveness ; 2nd, Its inconvenience ; 3rd, Its danger ; 4th, That it created a moisture on the inside of the pieces. Now I think that I can satisfy any one who who will make the necessary observations and .experiments, that these objections are well nigh, if not totally, unfounded, but before I undertake to make this appear, I must give a formula for its preparation, as this is a key to the answer I have to make. Take of dry nitrate of soda, 1 pound ; commercial sulphuric acid eight fluid ounces. Mix and distil as long as the acid comes over in profitable quantity. Of this (nitroso nitric acid) take four fluid ounces, commercial sulphuric acid two ounces, good picked cotton one ounce —mix the acids and pour them gradually upon the cotton in a wide shallow dish (I use a pudding dish), turning it over and over all the while that the atmosphere may have free access to it, otherwise it is liable to be injured or to take fire ; press the cotton together that the acid may penetrate the whole mass, then (as soon as convenient) press out as much of the acid as possiale and put it away to be returned to the retort for another distillation ; let it remain in this condition for several hours, then wash it thoroughly in cold water until no acid can be detected by the taste. (After this I usually wash in a solution of sal soda and again in cold water). Express all the water from it that can be done, and subject it at once to carding with coarse cards, which will facilitate its drying greatly. Expose it to a current of air to dry, after which have it well carded and made into rolls. As a last step, manufacture it into a loonely doubled and twisted cord of a size to suit the calibre of the price for which it is intended; clip into suitable lengths for cartridge, and it is ready to be used as such without further preparation. It will now be found to weigh one and a half ounces. It is thus more cheap-ly made into cartridge than gunpowder, and in this state is as convenient as it or any other substitute. Its bulk is so much reduced that fifty charges for a fowling piece maybe carried in the vest pocket. It is not mord liable than gunpowder to burst the gun, and I iiave satisfied myself completely that it does not heat the piece appreciably. It has been long known that it does not soil the gun, nor will it explode except by a spark or a temperature above 212 Fahr. As to the charge that it produces a moisture by its explosion, I have only to say that I have endeavored by frequent and rapid firing; to ascertain the fact, but have not done so except in an early experiment with an indifferent article, in a screw-barrel pistol, in which the ball was not driven out. Finally as to cost,—1 recollect that when this discovery was first promu gated, that some distinguished authority asserted that it could be produced at a cost of fltty cents per pound. This estimate was, however, thought to be greatly too low, both by those who undertook to prepare it, and especially by those who purchased it. Now, however, I feel well assured that it will be sold (as soon as it comes into general use) for considerably less than this. In lact this cost is scarcely exceeded in that manufactured in my office, where I have nothing but an apothecarys pestle, with which to express the acids, and where, consequently, two-thirds of itare washed and thrown away. I have not, as yet, prepared but a single ounce at one operation, but have no doubt that a pound may be prepared at a time with nearly as great facility, the only precautions necessary being to pour on the acids gradually in a large cool vessel, and to keep the mass turning over all the while. Marstons breech-loading fire-arms appear to be admirably adapted to the use ot this article. J. V. H.