Page:Popular Science Monthly Volume 58.djvu/509

Rh explosive as Maximite has an enormous advantage over explosives heretofore in use.

Maximite cannot be exploded by ignition. If a store-house filled •with this material were set on fire, there would he no danger of explosion. Melted cast iron may be poured upon a mass of Maximite without the least danger of exploding it. When heated, it melts, and if the heating be continued, it will evaporate like water, without producing an explosion. Lyddite, the high explosive adopted by the British Government, is said to be simply picric acid. This substance is melted for filling the shells, which are preliminarily heated to about the fusion point of the material to prevent too rapid setting. The melting point of picric acid is 122° C. The melting point of pure Maximite is exactly one-half of that of picric acid. That is to say, it is 01° C. The low melting point of Maximite enables it to be fused over the ordinary water bath, but owing to the impossibility of exploding it by heat, the water bath is not used, for it may be melted over an open fire in the same manner that asphalt is melted in the street cauldrons, and with equal safety. It is not necessary to heat the shells beforehand when filling them with Maximite.

On the other hand, great care has to be taken in the fusion of picric acid, because, if it becomes ignited in quantity before fusion, while in granular form, it will detonate, and also if it be heated very much above the fusion point, it will detonate.

The high fusion point of picric acid renders it necessary to employ a special lining material for protecting the shells against the erosive effect of the acid, while Maximite has very much less erosive action upon metals, and owing to its low fusion point an ordinary coating of shellac or similar substance is all that is necessary to protect the shells.

It has been found from the experiments made by the Government that, although a high explosive may be so sensitive as to safely with 1 stand the shock of acceleration in the gun. it may still be dangerous to fire, owing to the rapid rotation given to the projectile by the rifling of the gun, which is a rate of about 7,000 turns a minute. As a result, the projectile revolves upon the explosive before the latter has time fully to participate in its rotation. The great heat generated by this friction is apt to set fire to the explosive, causing a detonation.

Maximite requires so little heating for fusion that there is but slight contraction of the molten substance in reaching the point of solidification or freezing point. Maximite, furthermore, possesses the peculiar quality of expanding on solidifying, in the same way that Mater does on freezing. This causes it to set very firmly upon, and to