The Rationale

The smokelessness of the modern powder is the consequence rather than the direct aim of certain ends for which the chemist and the ordnance engineer were working. Smoke, as every one knows, is evidence of incomplete combustion; and, when the old black or brown powders were used, but a trifle over onethird of their bulk was consumed in the generation of propelling gases: the twothirds remaining were represented in smoke and inert or ineffective residue, which, together with the projectile, had to be driven out of the gun by the effective or active one-third. In other words, could the chemist find a properly combustible propellant-one that would be regularly and completely consumed within the gun-one pound of such an ideal powder would in effect be nearly equal to three pounds of the old brown or black powders. Apart from this sav

with absence of the fouling common to all smoky powders. The solution of the puzzle lay in the adaptation of gun-cotton as a basis for a new propellant-the substitution of a homogeneous substance for the mechanical mixture of the past.

Gun-Cotton the Basis

Gun-cotton, as most of us know, is the cotton of commerce made explosive by soaking it in a mixture of nitric and sulphuric acids, and then, by subsequent mechanical treatments, made into one of the safest and at the same time most powerful of explosives.

The propellant used in our Navy's ordnance is what is technically known as a "gun-cotton powder;" but the term "powder" is decidedly a misnomer, the units being perfectly-formed grains of varying size instead of the shapeless particles characteristic of a "powder" properly so called.

Soluble gun-cotton is that containing less than 12.75 per cent of nitrogen. This, when treated in a mixture of ether and alcohol, becomes a jelly-like substance which, after the solvent has been withdrawn or dissipated, becomes a hard, tough, translucent mass. Pressed into the form of grains, this substance will burn regularly and without smoke. It cannot be detonated by shock, and requires an ignition temperature of 185° C., which, while lower than that of the old powders, is misleading, for the substance is really less inflammable than the latter, and actually requires a starting or ignition charge of black powder. The small amount of smoke now seen at the time of discharge of our guns, is due almost entirely to the ignition charge of black powder.

Processes of Manufacture-Nitration

So much for the reasons and the results. Now for the manufacture. Cotton-seed waste, lint cotton, and card waste, after a proper cleansing in a caustic bath, and a thorough drying, are the materials used. This stuff is soaked for half an hour in a mixture of sulphuric and nitric acids-one pound of cotton to fifty pounds of acid mixture.

During nitration, a certain percentage of water is liberated, which, if not absorbed, would weaken the nitric acid and gradually lower the degree of nitration. The mission of the sulphuric acid is to absorb the water and thus maintain the strength of the nitric acid at its proper standard. The strength of the acid mixture, its temperature, the duration of the soaking, the initial dryness of the cotton, and even the condition of the minute mass of fibers as to their agglomeration, all bear directly upon the resultant product, both as to its nitration and as to its solubility. The nitration takes place in a centrifugal wringer, which, after the proper period of quiescence, is put in motion and drains the bulk of the acid from the mass. After this, the gun-cotton-for such it has become-is put in a large tank and washed or "drowned" in fresh water, and after that again washed in fresh water in another centrifugal wringer.

Every effort is now made to remove the least trace of residual acid, for it is this that most affects the stability or keeping qualities of the subsequent socalled powder. To this end, the gun-cotton is put into large vats and boiled for a couple of days, during which several changes of water are made. After this. the material is put in pulping machines

just like those used in a paper mill, where it is ground for fifteen or twenty hours, the water again being continually changed, and sodium carbonate added from time to time to neutralize any free acid still remaining in the cotton. From the pulpers, the cotton or pulp is moved to big, circular vats called "poachers," and is then steamed and stirred for a period of forty-eight hours. Fresh water is added frequently, and, after a proper time, the mass is allowed to settle and the top water drained off. By successive washings, settlings, and drainings, all traces of alkali are removed, and the pulp is then tested by heat for stability.

Mixing

The pulp must now be thoroughly dried and all water removed before subjecting it to the ether-alcohol. Large centrifugal wringers remove 75 per cent of the water; after which the pulp, like a thick paste, is fed onto a wide blanket belt and led through rollers that turn out the "pyro," as it is called, in flakes which feel not unlike slightly dampened crackers. In this flaky condition, the "pyro" is carried to the dehydrating press. Into the cylinder of this press is put fifty

pounds of the damp cotton; and, under a pressure of 200 pounds per square inch, the major part of the residual water is forced out, the material being at the same time formed into a compact cylindrical mass. The piston is withdrawn; twentyfive pounds of alcohol is poured in, on top of the cotton; the cylinder is closed; and air, under a pressure of 100 pounds, is turned in, on top of the alcohol. The result is that the alcohol is forced through the mass, driving the water before it. After most of the alcohol is out, which is not until the cotton has been subjected to a further pressure of nearly 3,000 pounds to the square inch, the remaining 25 per cent leaves the cotton in just the proper condition for the admixture of ether, which is added to the amount of half the weight of the mass, to provide the proper solvent.

In order to insure a thorough mixing, the cotton is next put in a "mixer"—the double of the mechanical kneader used in steam bakeries. There, after an hour, the solvent becomes thoroughly mixed with the cotton, and the mass looks and feels like damp, coagulated corn meal. From the mixer, the material is put into a press, and is formed into cakes weigh

ing about fifty pounds each. To the touch it is like crude rubber, and in appearance looks not unlike syrup-soaked maple sugar. Technically, the substance is now termed "colloid," and it actually is smokeless powder; but there are still a number of processes to be gone through before the material becomes the completely finished product.

To make sure, lowever, that the solution is complete, the rubbery mass is forced through a thick steel strainer under a pressure of two and a-half tons. It comes out in long cords of a pale straw

end of each wire being free-as there are to be perforations in the grain. The colloid is now forced through this die, backed by a pressure of from 4,000 to 6,000 pounds, depending, of course, upon the size of the grain. The colloid comes out in a continuous rod like an interminable, pale yellow snake, with a number of symmetrically disposed longitudinal perforations. As this rod passes to the end of the table or trough, it is run into a "cutter" which clips off the grains in proper lengths. The object of the longitudinal perforations is to admit the flame

to the interior of the grain, so that, as the exterior decreases under the attack of the gases, the interior surface of attack increases. The result is the maintenance of a uniform total area of combustion, and a consequent uniform development of propulsive gases. The result of this, in turn, is that the shot, during its run from breech to muzzle, receives a gradual increase of velocity as its inertia is overcome, and leaves the weapon with a much higher velocity than it is possible to secure on a given weight, with safety, by using black or brown powder-the rate of burning of which is either spasmodic,

as in the case of the black, or only relatively regular, as in that of the brown variety of the older propellants.

Drying

After the colloid has been made into grains, the next steps are devoted to drying it. The first of these processes is one of economy. At this stage the powder retains a large percentage of the solvent ether-alcohol, and to recover this is important. This is done by heating the powder, and reclaiming the volatile solvent by condensation. After this, the powder is put in drying houses, where the temperature is maintained uniformly throughout long periods. For the largesized grains, it takes about six months to dry out all but about 3.5 per cent of the solvent. During the process of drying, the grains change in color from a pale yellow to a deep golden brown, and by the time they are used in service the color is even darker.

Testing

At various stages of the manufacture, the chemist steps in and most careful analyses are made. Even after the powder has passed all these tests, a sample lot is stored away in a surveillance magazine, where, day by day, it is watched, and, should it be found lacking in stability, the ships carrying it are at once so informed and proper measures of safety taken. This, however, owing to the thorough and careful methods of governmental manufacture, has not been necessary for a long time.

That the powder is uniform in its working, must be determined by firing tests, in which the developed pressures are carefully checked; this is one of the duties devolving upon the United States Naval Proving Grounds, and the details of the work must be reserved for treatment in a separate article.

Smokeless powder, even with the improvement it represents over the old propellants, brings with its use its own problems. One of these, as we have seen from the recent accident on the battleship Missouri, is based on the presence of residual gases in the gun after discharge, and the danger of their ignition on the opening of the breech and the admixture of oxygen. The size and the shape of

A National Enterprise

When the government factory was established, there was a howl from the private manufacturers of powder; and, as the plant has increased, these private interests have persistently opposed it, but Congress has continued the necessary appropriations.

The economic results of the establishment of the plant have been many. The price of manufacture by private concerns is declared to have been unreasonably high-making due allowance for all business interests-and the Government demanded and secured a reasonable reduction. The quality of the product is maintained, and all of it chemically and ballistically tested, both that manufactured at the government plant and that made by private manufacturers. Moreover, improvements have been discovered and initiated, which private enterprise might