Nitroglycerin
2 of the 6 encyclopedias on this shelf carry an entry for Nitroglycerin. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a violently explosive substance, easily prepared by dissolving glycerin in a mixture of equal measures of the strongest nitric and sulphuric acids, previously cooled and pouring the solution in a thin stream into a large volume of water, when the nitroglycerin is precipitated as a colorless heavy oil (sp. gr. 1.6). It is advisable to add the glycerin to the mixed acids in very small quantities at a time, and to cool the mixture in a vessel of water after each addition. When the nitro glycerin has subsided, the water may be poured off, and the oil shaken several times with water, so as to wash it thoroughly. The formation of nitroglycerin resembles that of guncotton, three ng removed equivalents of hydrogen being remo from the glycerin by the oxidizing action of the nitric acid, and three equivalents of nitric peroxide introduced in their place. This oil is far more violent in its explosive effects than guncotton, more nearly resembling the fulminates, though not so easily exploded. For blasting rocks the nitroglycerin is poured into a hole in the rock, and exploded by the concussion caused by a particular kind of fuse charged with a little gunpowder. It has been stated to produce the same effect in blasting as 10 times its weight of gunpowder, and much damage has occurred from the accidental explosion of nitroglycerin in course of transport. A drop of nitroglycerin is said to cause very violent headache, and in arger doses is decidedly poisonous.
Aiton's Encyclopedia (1910)
ni-tro-glis'er-in, a powerful explosive agent. It is a light yellow, oily liquid produced by the action of nitric acid and sulphuric acid on glycerin. It is 1.6 times as heavy as water. When struck a quick, hard blow, or heated rapidly to 306 deg. F. It explodes with terrific violence. It is a poison, but may be administered in minute doses as a remedy for heart failure. It was discovered in 1864. Pound for pound, it has about three and one-half times the force of powder, but it acts so quickly that it is more effective than powder in blasting large masses of rock. Nitroglycerin is too dangerous for ordinary use. See Dynamite
What Has Changed in the Last Century
Aiton's 1910 entry dates the discovery to 1864, the year Alfred Nobel began manufacturing it; in fact Ascanio Sobrero made the oil in Turin in 1847, and 1864 is better remembered as the year an explosion at Nobel's works killed his brother Emil. Both accounts treat it chiefly as a blasting agent "too dangerous for ordinary use"; today nitroglycerin-based dynamite has been almost wholly displaced in mining and quarrying by ammonium nitrate mixtures (ANFO) and emulsion explosives, which are far more stable and cheaper. The medical use Aiton mentions in passing, "minute doses as a remedy for heart failure", is now the larger story: nitroglycerin tablets and sprays remain a standard treatment for angina, and the "very violent headache" Collier's noted in 1921 was the clue to why. It works by releasing nitric oxide, which relaxes blood vessels ott, Ignarro and Murad shared the 1998 Nobel Prize in Physiology or Medicine for working that out.
Written for this edition, 2026.