Nitro-glycerine (known also as Glonoin or Glonoin-oil) can be readily prepared by dissolving glycerine in equal measures of strong nitric and sulphuric acids and pouring the solution into water, when the nitro-glycerine becomes precipitated. Nitro-glycerine was discovered by Sobrero, a young Italian chemist at Paris, who in 1846 found that by the above process he could produce a highly explosive mixture. There was little idea at the time of the value of the discovery, which was treated solely as a chemical curiosity, until about fifteen years later, when Alfred Nobel, a Swedish engineer and chemist, perceiving the value of the unrecognised explosive and turning his attention to its development, rapidly introduced it as a blasting agent for industrial purposes. The new explosive was eminently satisfactory so far as blasting power was concerned; but a series of fearful accidents, notably that to the ship European at Panama in 1866—numerous expedients devised to render it safe in transit notwithstanding—called public attention to the danger inseparable from its conveyance, and in 1869 parliament, so far as Britain was concerned, placed its veto on nitro-glycerine.
The drawbacks which culminated in this prohibition led to the production of the nitro-glycerine compounds, now forming a large group, notably dynamite (see DYNAMITE, Vol. IV. p. 144), in which nitro-glycerine, absorbed by some inert porous substance, is thereby rendered safe from the dangers incident to the employment of nitro-glycerine without such treatment. Nitro-glycerine, as manufactured on a large scale for commercial purposes, is formed by the mixture of strong nitric and sulphuric acids, cooled by water, previous to being introduced into a large leaden vessel, the temperature of which is kept down by water circulating through coils inside. Glycerine is then injected by compressed air as a fine spray, and becomes immediately nitrated, considerable heat being evolved. On the completion of the nitration, as indicated by the fall of temperature, the mixture is run off into another leaden vessel and allowed to stand. In about an hour the separation is complete. The nitro-glycerine, after being thoroughly washed in water and subsequently in an alkaline solution to remove every trace of acid, is ready for manufacture into dynamite or other nitro-glycerine compounds.
The utmost care is exercised in the above processes, and any abnormal rise in temperature is strictly guarded against, or accidents would arise. For similar reasons the materials employed in the manufacture of nitro-glycerine are in every particular the best and purest attainable. Colourless when pure, but having as an article of commerce a pale brown colour, nitro-glycerine is a dense, oily liquid, having a specific gravity of 1.6. It is inodorous, but has a sweet, pungent, aromatic taste; a single drop, however, if placed on the back of the tongue, will produce headache and pain in the back lasting for hours. By those accustomed to handling this substance, no inconvenience whatever is experienced. Nitro-glycerine enters into medical prescriptions for certain diseases of the heart.
If ignited in the open air nitro-glycerine burns rapidly and with a brisk flame without any explosion; and if poured out in a thin sheet it ignites with difficulty and burns incompletely; but it explodes at once if it is exposed to a moderately strong blow or concussion, to the concussion due to the explosion of gunpowder, to contact with red-hot iron, and especially to the action of detonating mixtures and fulminates. It likewise explodes on exposure to a high temperature, the exploding-point for nitro-glycerine compounds being about .; but to . is sufficient to set up decomposition in the cartridge, and this will quickly raise the temperature to exploding-point. According to Dr Rudolf Wagner, nitro-glycerine, if chemically pure, may be cooled down to without becoming solid; that of commerce, however, becomes solid if exposed for a considerable time to a temperature of about to ., crystallising in long needles, which are most dangerous to handle, since they explode, even if gently broken, with much violence. In such condition the nitro-glycerine compounds should not be used for blasting, but can be readily thawed in a simple form of pan heated by hot water. At nitro-glycerine begins (according to Adriani) to decompose, giving off red vapours; and if the heat be suddenly applied, or slightly raised above this point, violent explosion will occur. For equal bulks nitro-glycerine is calculated to be thirteen times as strong as gunpowder, while for equal weights it is eight times as powerful.
Nitro-glycerine compounds have been employed in the largest blasts that have been made, notably those at Hell Gate (see BLASTING). The manufacture of nitro-glycerine compounds in Great Britain is strictly controlled by legislation, and carried on under government supervision. See Eissel, Handbook of Modern Explosives (1891).