Pure Nitro-Glycerin is nearly colorless; usually, however, owing to coloring matter contained in the Glycerin used in its manufacture, it is of a light yellow-tinted color, oily, without odor, but having an aromatic taste, Sp. Gr. 1.6 at 60°F, very insoluble in water; mixes with alcohol (one part to four parts) and ether; it separates from the alcoholic solution by the addition of water. A vinous taste is perceptible to the tongue, the maxillary glands are stimulated, and in a few minutes the individual who has tasted it from a pin’s point for the first time, is conscious of a persistent, throbbing headache. Slightly touching, it with the hands produces a like effect; after a few days of frequent handling, however, the system becomes less susceptible to these effects, and workmen constantly employed in its manufacture are not affected by it. It is poisonous, a small quantity being sufficient to kill a dog, (Sobrero). It decomposes at 320°F, giving out red vapors, and explodes at a higher temperature, or by concussion or percussion, crashing the containing vessel; it ignites by flame, and burns without explosion, yielding a light ethereal flame of considerable volume.
Pure Nitro-Glycerin may be kept for a year unchanged, (De Vrij). The writer has exposed it to frost, sun and rain, for three years, and found it unchanged. Unless perfectly pure, however, it rapidly changes, becoming of an orange yellow color, evolving fumes, and seems to become a wholly differing compound, being difficult, when thus changed, to congeal, except at a much lower temperature than 45°F, and is more readily exploded.
It very easily decomposes by drying in a warm room with rarefied air, (Williamson).
It is instantly decomposed when dissolved in alcohol, by adding an alcoholic solution of caustic potash, the reaction being so violent as to eject the mixture from the test tube.
Nitro-Glycerin in contact with the following salts: nitrates of lime, cobalt, soda, barytes and potash; chlorides of calcium, of barium; perchloride of iron, carbonate of lime, sulphates of potash, lime and soda, was found unchanged after a year’s exposure.
Incompatibles: nitrate of silver precipitates black oxide of silver; nitrate of copper gives a precipitate of peroxide of copper, the Nitro-Glycerin remaining, however, bright and apparently unchanged. In a solution of nitrate of mercury, there appears a white film, a bubble of protoxide of azote, apparently adherent to the Nitro-Glycerin. Muriate of ammonia seems to divide the Nitro-Glycerin into two liquids, a light film supernatant, and the heavier liquid subjacent. The action of chloride of mercury (calomel) is but very slight. Protochloride of tin forms a precipitate of peroxide of tin, the residuary Nitro-Glycerin reflecting light powerfully, and as brightly as a diamond. Bichromate of potash is partly reduced to chromate. Sulphate of copper forms a very slight precipitate of oxide of copper, with apparently no change in the residuary Nitro-Glycerin. Sulphate of iron decomposes it, giving a voluminous precipitate, with evolution of nitrous fumes. Sulphuret of ammonia decomposes it, with precipitation of sulphur. Acetate of lead, chlorine water, ferridcyanide of potassium, cyanide of potassium, sulphocyanide of potassium, and of mercury, nitroprusside of sodium decompose it, also the sulphurets of iron, and potassium.
The action of tin, iron, and lead, slowly decomposing the Nitro-Glycerin, especially in the presence of an acid, indicates that metals having an affinity for oxygen, are the most active in promoting decomposition, evolving at the same time nitrous fumes, or protoxide of nitrogen, whilst the residuary Nitro-Glycerin does not seem to be affected; with sulphuretted hydrogen, as with sulphuret of sodium, potassium and ammonium, the action is prompt, and if these reagents be added in sufficient quantity, the Nitro-Glycerin is wholly decomposed, sulphur being precipitated.
Ascagne Sobrero, the discoverer of Nitro-Glycerin, says: it may be prepared by slowly introducing syrupy Glycerin into a mixture of two volumes concentrated sulphuric acid to one volume of nitric acid, Sp. Gr. 1.4, dropping it in and rapidly cooling. It seems to dissolve in this mixture without any noticeable reaction, and by pouring it into water, the so formed Nitro-Glycerin separates from it. It is then washed several times in water, is next dissolved in ether, and after evaporation (dangerous work this) is finally purified over sulphuric acid.
De Vrij recommends dissolving 100 grammes of Glycerin Sp. Gr. 1.262 in 200 c. c. of hydrated nitric acid cooled to 14°F, taking care that the mixture never exceeds in temperature 32°F. When a homogeneous mixture has been obtained, 200 c. c. of strong sulphuric acid are added very gradually, taking especial care that the temperature of this mixture never rises above 32°F. The oily Nitro-Glycerin which floats on the surface is separated by a tap-funnel from the acid liquid (which yields more Nitro-Glycerin on being diluted with water) and is now dissolved in the smallest possible quantity of ether; this solution is shaken with water, until the water no longer reddens litmus; the ether evaporated (here take care!) and the remaining Nitro-Glycerin heated over the water-bath till its weight remains constant. Merck, of Darmstadt, the eminent operative chemist, found in following De Vrij’s method, whilst evaporating the ethereal solution, and before the temperature had reached 212°F, it was accompanied by a terrible explosion. An accident from the same cause occurred in the laboratory of Dr. E. Von Gorup-Besanez, and we find in “Comptes Rendus” an account of the effects of the explosion of only 10 drops of Nitro-Glycerin, which, by one of the pupils of that chemist, in his laboratory, were put into a small cast-iron saucepan, and heated with a Bunsen gas flame. The effect of the explosion was that the forty-six panes of glass of the windows of the laboratory were smashed to atoms, the saucepan was hurled through a brick wall, the stout iron stand on which the vessel had been placed was partly split, partly spirally twisted, and the tube of the Bunsen burner was split and flattened outwards. Fortunately, none of the three persons present in the laboratory at the time were hurt. When Nitro-Glycerin is caused to fall drop by drop on a thoroughly red hot iron plate, it burns off as gunpowder would do under the same conditions; but if the iron is not red hot, but yet hot enough to cause the Nitro-Glycerin to boil suddenly, an explosion takes place.
Nitro-Glycerin is decomposed by evaporation, even in vacuo, over sulphuric acid at ordinary temperatures (Railton), and when left to itself, frequently undergoes spontaneous decomposition; but when well purified, it may be kept for a long time without alteration (H. Watts); exhibits different properties, according to the manner in which it is prepared (Gladstone).