The sulphur acts upon the carbonate of potassa, producing liver of sulphur," a mixture of the sulphide with the sulphate of potassa; this is suddenly oxidized by the decomposition of the nitric acid, and nitrogen gas is liberated. The experiment should be tried with a small quantity only, say as much as will cover the tip of a knife blade. (See Gunpowder.) -Pyroxyline. In the explosives classed above under gunpowder, the sulphur plays the part of a stimulant of chemical action, by its superior readiness to ignite. It is the nitric acid and the carbon which, forming voluminous gases, generate the explosive force; and these substances can be brought together in such ways as to form explosive compounds which have the' advantage of leaving no solid residues or smoke. Pyroxyline is the name given to the class of detonating substances produced by the action of concentrated nitric acid upon the cellulose of cotton, hemp, paper, sawdust, etc. Gun cotton was discovered in 1846 by Schon-bein, and also by Bottger. The conversion of cotton into gun cotton by the action of nitric acid scarcely changes its outward appearance. Chemically, it contains much hyponitric acid. It will ignite at 50° to 150° C, and leaves no residue after explosion.

Its effectiveness is variously estimated at from two to six (probably four) times that of gunpowder. According to the best modern formula, gun cotton is trinitro-cellulose, C6H7(NO2)3O5 . The products of combination are entirely gaseous. Karolyi gives the following, in 100 parts:

CONSTITUENTS.

By volume.

By weight.

Carbonic oxide............

28.55

28.92

Carbonic acid.........

19.11

30.43

Marsh gas.......................

1117

6.47

Binoxide of nitrogen................

8.83

9.59

Nitrogen.........................

8.56

8.71

Carbon..............

1.85

1.60

Aqueous vaper.........................

21.93

14.28

100.00

100.00

When burned under pressure, the nitric oxide reacts more completely with the carburetted hydrogen, and the result of this and other causes is a greater volume of evolved gases. The actual product of heat units as compared with the combustion of gunpowder is proportional, according to Dr. Craig, to the respective amounts of oxygen concerned in the two cases; but the greater volume of the gases from gun cotton renders their temperature lower and their mechanical effect greater. This material burns without explosion when ignited in the open air. Ordinary percussion sometimes ignites it-a source of peril in packing bore holes. The acid and aqueous gases which it evolves have prevented its use in ordnance; moreover, it is very hygroscopic and liable to spontaneous decomposition, sometimes leading to explosion, rendering its storage perilous. Many of these objections, together with that of bulk, have been removed by Abel's process of manufacturing gun cotton in compressed solid cylinders, which burn harmlessly, can be stored and transported with safety, and explode with great power when ignited under confinement by means of a detonating powder. The experiments of Gen. Lenk, in Austria, led to this improvement. The compressed gun-cotton is adopted in that country for artillery.

Gun cotton is used as a filter for strong acids, and also (dissolved in ether) as a varnish. (See Collodion, and Gun Cotton.)-Xyloidine is the white, pulverulent, and very explosive substance obtained by Braconnet in 1833, by treating starch with concentrated nitric acid. Lithofracteur is the name originally given to a white blasting powder, consisting of coarsely ground saltpetre and sulphur, with a third substance, supposed to be sawdust or bran, treated with nitric acid. The improved lithofracteur described below is a different substance.-Schultze's chemical powder, sometimes called wood gunpowder (introduced in 18G4), contains no sulphur; and the charcoal is replaced with wood which has been triturated, deprived of its acids, soluble salts, pro-teine, and albumen, and treated with concentrated sulphuric and nitric acid. These grains of wood are subsequently saturated with nitrate of potash or baryta, or both, and dried. The powder can be wet and dried again without weakening it; hence it may be kept or transported in a damp state with perfect safety. It is about one third as dense as gunpowder, is more powerful, and leaves but a trifling residue. But it seems to have been superseded by nitroglycerine compounds. Some inexplicable explosions have occurred with it.

The gases produced from it in mining have been complained of, possibly without good reason.-Haloxvline is a powder tried in Austria, which contains no sulphur, and in which the charcoal is apparently represented by woody fibre. Like the slow-burning Neumeyer powder, it gives comparatively little noxious gas, is hygroscopic, and works better in solid than in fissured rocks. It is asserted to burn harmlessly in the air; but like many other "harmless" powders, it has given rise to some strange and disastrous explosions. The above account of its composition follows the Ocsterreichische Zeitschrift (1866 and 1867); Wagner's Technology (1870) says it contains charcoal, nitre, and yellow prussiate of potassa.-Nitro-glyce-rine. This substance, known also as fulminating oil, nitroleum, trinitrine, glyceryl nitrate, and glonoine, and undoubtedly the most important explosive since gunpowder, was discovered in 1847 by Sombrero, then a student with Pe-louze in Paris. It is formed by treating glycerine with concentrated sulphuric and nitric acid. (See Glycerine.) Until 1864 it found no practical application, except as a homoeopathic remedy for headaches similar to those which it causes.

In that year Alfred Nobel, a Swede of Hamburg, began its manufacture on a large scale, and, though he sacrificed a brother to the terrible agent he had created, has persevered until in its later and safer forms nitro-glycerine has come into wide use and popularity. It is a clear, oily, colorless, odorless, and slightly 'sweet liquid, heavier than water and insoluble in it, but soluble in ether and methyl alcohol; crystallizes in long needles at 4° to 11° C. At -15° C. it becomes after a while thick; prolonged exposure to -2° 0. solidifies it. It detonates in the open air, under a strong blow or shock; ignites with difficulty when poured out in a thin sheet, and even then burns incompletely without explosion. It can be evaporated at 100° C, if boiling is avoided; but boiling, or the temperature of 180° O., causes an explosion. Confined or frozen, so as to permit the instantaneous transmission of an impulse through the mass, it will explode, sometimes under a very slight shock. It is usually exploded with a detonating fuse. When badly prepared or preserved, it is liable to decomposition, yielding gases which exert a pressure within the containing vessel and create a condition of perilous sensitiveness to external shocks.