138

GUNPOWDER.— Materials. Charcoal.

680°

C80 to 698

698 to 716

112 to 1472

Violette further examined several varieties ofcharcoal, all of which were prepared at 572° by boththe foregoing methods ; they inflamed between 680°and 710°, but in no case did they take fire at a lowerheat than 680°. He observed that t^e charcoalsfrom light woods generally ignited a little before theproduct from the harder kinds, with the exceptionof one, which is remarkable, namely, the charredproduct of the fungoid excrescence of the willow tree(agaric de saule). The latter was observed to takefire in one instance at a temperature so low as 572°,and in every experiment at 608°. Hence it is themost inflammable of all species of charcoal; and asthe above-named investigator remarks, had it beenprepared at 500° instead of at 572°, doubtless itsspontaneous combustion would take place at a lowertemperature than even that given. It may well beinquired to what may this peculiarity be attributed ;and doubtless, as Yiolette suggests, the organicmolecular state of the substance might exercise someinfluence whereby its rapid ignition is induced.

To sum up these results, it will be seen—

1. That the ignition of the most inflammable of allwood charcoals ('agaric de saide') takes place at 572°.

2. That the charcoals from different kinds of wood,when prepared at a constant heat of 572°, spontane-ously ignite between 698° and 734°, according to thenature of the wood producing them ; but that theproduct from the lighter burns quicker than that ofthe denser woods.

3. That charcoals from the same wood, but pre-pared at increasing temperatures, spontaneouslyundergo combustion at very unequal degrees ofheat, as already shown.

After attentively considering these results, verylittle doubt will remain as to the best means of car-bonizing the wood. To a certainty the temperatureof the charcoal, as prepared by most of the methodsindicated under the charring of wood, and alsounder Acetic Acid , exceeds the limits laid downby Violette ; and therefore it follows that evi-dently the choice should be decided in favour ofthat method which furnishes the charcoal at thelowest degree of heat. There are three methods inordinary use by which the charcoal for the powdermanufacturer is prepared, namely, the pit, the fur-nace, and the closed retort. When pits areselected, they are made smaller than those described

260°

—

500°

340° —

270

—

518"

280

—

536

340

to

3G0 —

290

—

554

300

—

572'

310

—

590

320

—

608

330

—

026

■

360

to

370 —

340

—

644

350

—

662

432

—

819 J

1023

1873-6 1

1250

1300

—

2282

2372

i

600

to

800 —

1500

—

2732

j

Charcoals made")

at temperatureswhich fuse pla-

J-1250

2280

tinum, .

•J

in the foregoing articles, and the walls and sides,together with the apertures for the introduction ofair, are constructed with more care; the wood isalso arranged in them with greater caution, and thecombustion watched so that during the operationthe whole may be completely acted upon, and nohalf-burned material left. In the general particulars,however, no difference exists between the methodsalready alluded to and this, so that it will be need-less to repeat the description. The product amountsto 26 or 27 per cent, of the wood. If the carboniza-tion is effected in furnaces, the quantity of the pro-duct will not bo so large ; besides the consumptionof fuel will be greater than in the preceding case. InEngland, however, the charcoal obtained by the dis-tillatory process in closed retorts is always preferred.

The wood is now converted into charcoal by heatingit in iron cylinders, and the combustible gases passunderneath the cylinders of an adjoining set, andconstitute the greatest part of the fuel. In thecylinder house of Messrs. John Hall and Sons thegases are so thoroughly economized by the methodwhich they have originated that, whereas in 1869; 1cwt. of coal was required for every burning, at thepresent time (1877) fifty burnings can be effectedwith 56 lbs. of coal. The amount of charcoal isgenerally 20 per cent, of the wood employed. Afterthe charcoal is taken from the cylinders, it is placedin iron coolers provided with tightly-fitting lids, andallowed to stand for twenty-four hours, by whichtime it is quite cold, and it is then shot into storebins. A. F. Hargreaves has found by experimentthat charcoal ground within two days of carboniza-tion absorbs mechanically within its pores a largequantity of oxygen from the atmosphere ; now as thecondensation of all gases liberates heat, and char-coal being a bad conductor, the heat cannot escape :this becomes a source of danger. The maximumamount of oxygen (about 6‘9 per cent.) is absorbedwithin the first two weeks, and after this no changetakes place beyond those due to atmospheric agencies.

Good charcoal should submit to three tests. Itought to act as little as possible mechanically, evenon copper ; no salts should be extracted from it bytreating it with boiling distilled water ; and it oughtto give out no smoke when heated. The latter testis indicative of its being thoroughly burned.

Before entering upon the description of the pro-cess for compounding the substances which constitutegunpowder, it may be well to give a few additionalfacts relative to the circumstances which affect themutual decomposition of those bodies as they existin this article, and render the phenomena of its ex-plosion more easy of comprehension. Already someexperiments of Proust have been adduced, whichelicit comparative data of the explosiveness of certainvarieties of charcoal when mixed intimately withsaltpetre; but they do not afford any real knowledgeas to the degree of heat required to bring aboutsuch a metamorphosis, although they indicate thatsome kinds of charcoal form more inflammable mix-tures with nitrate of potassa than others. Theinvestigation of Violette upon the temperature at