Nitroglycerin

English

In 1846, the same year that Schönbein was creating nitrocellulose, the Italian chemist Ascanio Sobrero was also working with the mixture of sulfuric and nitric acids known to add nitro groups (NO2) to organic molecules (like cellulose, sugar, starch, and others).

The son of a doctor, Sobrero studied medicine in Torino (Turin), and had been authorized to practice as a physician in 1834, when he was 22 years old. Following his father's example of a physician who taught at the university, Sobrero took the examination to be a teacher, but due to political differences, he was classified as unsuitable.

Disappointed, he decided to leave medicine for the study of chemistry. He worked for about four years as an assistant in an Italian laboratory of general chemistry, and then a laboratory of pharmaceutical chemistry. His uncle, Baron General Carlo Rafaele Sobrero, was the general director of the Chemical Laboratory of the Arsenal in Torino, and had studied chemistry at Paris at the Ècole Polytechnique. His uncle had become acquainted with several famous European chemists, such as Thèophile-Jules Pelouze and Jöns Jacob Berzelius.

With a letter of recommendation from his uncle, Sobrero left for France, where he studied under Thèophile-Jules Pelouze, and became his assistant in the Frenchman's private laboratory, from 1840 to 1843. Pelouze had experimented with nitrating cellulose in 1838, and was still actively investigating the action of nitric acid on organic substances during the time Sobrero was assisting him.

Sobrero left Paris in 1843 to study under the famous German chemist Justus Freiherr von Liebig at the University of Giessen. Liebig has been called one of the greatest chemistry teachers of all time. He was instrumental in developing the study of organic chemistry, and the modern laboratory-based teaching of chemistry. For a chemistry student interested in teaching, this was a perfect opportunity.

Having been away from Italy for three years, Sobrero returned to Torino, where he worked again as a general chemist. In 1845, he received the appointment to the chair of chemistry at a new school.

Sobrero had been working with nitric acid and glycerin to produce oxalic acid, and had added nitric acid to the oil from birch trees, following work he had done with Pelouze. When Schönbein published his results with guncotton, Sobrero tried the new recipe (two parts sulfuric acid to one part nitric, a mix where the sulfuric acid acts as a catalyst for the nitration reaction) on glycerin. He also successfully made explosive compounds by nitrating the sugars mannose, sucrose, and lactose.

He reported his findings in a letter to Pelouze in Paris, who read the letter to the Acadèmie des Sciences there in 1847, a year after the discovery. In the letter, he cautioned about tasting the new chemical, since when he (and others in the lab) tried this on several occasions to test its toxicity, they all got severe headaches. As a vasodilator, nitroglycerin dilates capillaries in the brain, causing the headaches. By the end of the century, nitroglycerin was being used by physicians everywhere to treat the pain of severe angina, and is still used by heart patients today.

When Sobrero added the acids to glycerin, he saw a violent reaction take place, with lots of red fumes. However, if he carefully added the glycerin to the acid instead, while stirring it in an ice bath at o° Celsius, the glycerin dissolves. When the acid solution with dissolved glycerin is then added to water, nitroglycerin precipitates out, sinking under the water to the bottom of the dish.

Nitroglycerin

He washed the oily residue in more water, and then dried it in a vacuum over sulfuric acid (which has a great affinity for water, and thus helps desiccate things). The result was something with the appearance of olive oil (pure nitroglycerin has no color). In a paper he later presented at the Ninth Italian Scientific Conference in Venice, he describes the new compound:

It detonates when brought into contact with metallic potassium, and evolves oxides of nitrogen on contact with phosphorus at 20° to 30° C, but at higher temperatures it ignites with an explosion... When heated, nitroglycerin decomposes. A drop heated on platinum foil ignites and burns fiercely. It has, however, the property of detonating under certain circumstances with great violence. On one occasion a small quantity of an ethereal solution of nitroglycerin was allowed to evaporate in a glass dish. The residue of nitroglycerin was certainly not more than 2 or 3 centigrams. On heating the dish over a spirit lamp a most violent explosion resulted, and the dish was broken into atoms.

...The safest plan for demonstrating the explosive power of nitroglycerin is to place a drop upon a watch glass and detonate it by touching it with a piece of platinum wire heated to low redness. Nitroglycerin has a sharp, sweet, aromatic taste. It is advisable to take great care in testing this property. A trace of nitroglycerin placed on the tongue, but not swallowed, gives rise to a most violent pulsating headache accompanied by great weakness of the limbs.

Sobrero thought that one of his nitrated sugars, nitromannite, might make a good explosive for use in percussion caps. But in 1853, an explosion of 400 grams of the material in a laboratory at his uncle's arsenal caused such damage that he stopped pursuing the project. This may have also led to him not pursuing nitroglycerin as a commercial explosive.

That job ended up with Alfred Bernhard Nobel.

Nobel's father, Immanuel had, after several failed business attempts, finally done well as a manufacturer of machine tools and explosive mines, after moving to St. Petersburg, Russia from his native Sweden. The now prosperous family could afford private tutors for Alfred and his brothers. By age 16, Alfred was a knowledgeable chemist, having been tutored by chemist Nikolai Zinin (known as the father of Russian chemistry, who also taught Mendeleev) and fluent in five languages.

In 1850, at the age of 17, he spent a year in Paris studying chemistry at the laboratory of Thèophile-Jules Pelouze; three years after Pelouze had read Sobrero's paper to the French Academy. He then traveled in Italy, Germany, and the U.S., where he worked for John Ericsson, the Swedish engineer who later built the ironclad ship Monitor for Union forces in the Civil War.

When the Crimean War broke out in October of 1853, Immanuel Nobel's company in Russia was making a new type of underwater mine, experimenting unsuccessfully with the newly invented nitroglycerin, but succeeding with gunpowder. These mines were used in the Baltic to defend Russian ports from the combined French and British fleets. Alfred had returned to St. Petersburg in 1852, and worked with his father during the war. Regarding nitroglycerin, he later recalled:

The first time I saw nitroglycerine was in the beginning of the Crimean War. Professor Zinin in St. Petersburg exhibited some to my father and me, and struck some on an anvil to show that only the part touched by the hammer exploded without spreading. His opinion was that it might become a useful substance for military purposes, if only a practical means could be devised to explode it... My father tried to explode it during the Crimean war, but completely failed to do so... My father's later experiments with gunpowder mixed with nitroglycerine were all on a small scale.

When the war ended in 1856 with Russia's defeat, the bottom fell out of the Russian exploding mine business, and by 1859, Immanuel Nobel was once again bankrupt, and left Russia to return to his native Sweden. Alfred and two of his brothers remained in St. Petersburg, doing mechanical engineering work. Alfred carried on experimenting with nitroglycerin in St. Petersburg. He finally got nitroglycerin to explode underwater, by surrounding a glass tube full of the liquid with gunpowder in a zinc can, and using a fuse to set off what was basically a firecracker.

In 1863, he left St. Petersburg to rejoin his father in Stockholm, where he continued his experiments with nitroglycerin. He obtained a patent for improvements in the method of producing nitroglycerin as an industrial explosive, and for the blasting cap.

In 1864, the small shed he used for manufacturing the blasting oil exploded, killing his younger brother Emil, and several others. Undaunted, he continued his research. In 1865, he improved on the blasting cap, and moved the company to Krümmel, near Hamburg, in Germany, but the plant in Krümmel also exploded. Taking his experiments onto a raft in the river Elbe, he found that a highly absorbent diatomaceous earth could hold so much nitroglycerin that it will still explode, even when the earth still has the form of a powder. He calls his invention dynamite. Later in that year, he starts the United States Blasting Oil Company in the U.S.

In Nobel's 1866 U.S. patent application for his blasting powder, he not only describes the substance, and how to make it, but also how to use it, and detonate it. He even inserts a plug for his other invention, the blasting cap:

TO ALL WHOM IT MAY CONCERN:

Be it known that I, Alfred Nobel, of the city of Hamburg, Germany, have invented a new and useful Composition of Matter, to wit, an Explosive Powder.

The nature of the invention consists in forming out of two ingredients long known, vis, the explosive substance nitro-glycerine, and an inexplosive porous substance, hereafter specified, a composition which, without losing the great explosive power of nitro-glycerine, is very much altered as to its explosive and other properties, being far more safe and convenient for transportation, storage, and use, than nitro-glycerine.

In general terms, my invention consists in mixing with nitro-glycerine a substance which possesses a very great absorbent capacity, and which, at the same time, is free from any quality which will decompose, destroy, or injure the nitro-glycerine, or its explosiveness.

It is undoubtedly true, as a general rule, that nitro-glycerine, when mixed with another substance, possesses les concentration of power than when used alone; but while the safety of the miner (to prevent leakage into seams in the rock) prohibits the use of nitro-glycerine without cartridges, which latter must of course be somewhat less in diameter than the bore-holes which are to contain them, the powder herein described can be made to form a semi-pasty mass, which yields to the slightest pressure, and thus can be made to full up the bore-hole entirely. Practically, therefore, the miner will have as much nitro-glycerine in the same height of bore-hole with this powder as with nitro-glycerine in its pure state.

This is the real character and purpose of my invention; and in order to enable others skilled in the art to which it appertains (or with which it is most nearly connected) to make, compound, and use the same, I will proceed to describe the same, and also the manner and process of making, compounding, and using it, in full, clear, and exact terms.

The substance which most fully meets the requirements above mentioned, so far as I know or have been able to ascertain from numerous experiments, is a certain kind of silcious earth, or silicic acid, found in various parts of the globe, and known under the several names of silicious marl, tripoli, rotten-stone, &c. The particular variety of this material which is best for my compound is homogeneous, has a low specific gravity, great absorbent capacity, and is generally composed of the remains of infusoria.

So great is the absorbent capacity of this earth, that it will take up about three times its own weight of nitro-glycerine and still retain its powder-form, thus leaving the nitro-glycerine so compact and concentrated as to have very nearly its original explosive power; whereas, if another substance, having less absorbent capacity, is used, a correspondingly less proportion of nitro-glycerine will be absorbed, and the powder be correspondingly weak or wholly inexplosive.

For example, most chalk will take but about fifteen percent of nitro-glycerine and retain its powder-form. Twenty per cent, will reduce it to a paste.

Porous charcoal has also a considerable absorbent capacity, but it has the defect of being a combustible material, and also of less elasticity of its particles, which renders it easy to squeeze out a part of its nitro-glycerine.

The two materials are combined in the following manner:

The earth, thoroughly dried and pulverized, is placed in a wooden vessel. To it is introduced the nitro-glycerine in a steady stream so small that the two ingredients can be kept thoroughly mixed.

The mixing may be effected by naked hand, or by any proper wooden instrument used in the hand, or by wooden machinery.

Sufficient nitro-glycerine should be used to render the compound explosive, but not so much as to change its form of powder to a liquid or pasty consistency.

Practically, about sixty parts, by weight, of nitro-glycerine to forty of earth, forms a useful minimum, and seventy-eight parts, by weight, of nitro-glycerine to twenty-two of earth, the useful maximum of explosive power. The former has a perfectly dry appearance, the latter is pasty.

Between these two extremes the composition will be explosive powder, and will be more easily exploded, and its explosive power greater, as the relative proportion of the nitro-glycerine is greater.

The proportions, by weight, of seventy five of nitro-glycerine and twenty-five of earth, gives a powder as well adapted to ordinary practical purposes as that from any proportions I am now able to name, and can be easily compressed to a specific gravity nearly equal to that of pure nitro-glycerine.

When the mass has been intimately mixed and thoroughly incorporated by stirring and kneading, it is rubbed through a hair, silk, or brass-wire sieve, (iron corrodes) and any lumps which may remain are rubbed with a stiff-bristle brush till they are reduced and made to pass through the sieve.

The powder is then finished and ready for use.

The fineness desired for the powder will determine the fineness of the sieve to be used.

The chief characteristic of this powder is its nearly perfect exemption from liability to accidental or involuntary explosion.

It is far less sensitive than the nitro-glycerine to concussion, and contained in its usual packing, (a wooden cask or box) the latter may be smashed completely to pieces without any danger of an explosion.

Unlike gunpowder, in the open air or in ordinary packing, (a wooden cask or box,) it burns up, when set fire to, without exploding. It can, therefore, be handled, stored, and transported with less danger than ordinary gunpowder.

When confined in a tight and strong enclosure it explodes by heat applied in any form when above the temperature of 360° Fahrenheit. Under all other circumstances it may be exploded by some other explosion in it or into it.

The most simple and certain method known to me of exploding it is as follows:

The end of a common blasting-fuse is inserted into a percussion-cap, and the rim of the cap crimped tightly and firmly about the fuse by nippers, or other means, so as to leave the fulminating-powder of the cap and the end of the fuse tightly and firmly enclosed together. The end of the fuse, with the cap attached, is then embedded in the powder — the more firmly, the more certain the explosion.

In blasting, the powder is pressed tightly about the cap and fuse, and tamping, of sand or other proper material, added, and pressed but not pounded in. A tamping firmly pressed is as good as if rammed in the most solid manner.

The fuse explodes the cap, and this explosion explodes the powder.

I will add here that by carefully packing the end of a good fuse amidst the powder of a charge enclosed, like a blasting charge, in a tight place, the fuse alone will explode the powder, especially if the powder is strongly charged with nitro-glycerine. But this method of explosion requires too much care, and is too uncertain to be depended upon or generally used.

As before stated, the more strongly the powder is charged with nitro-glycerine the more easily it explodes. If, therefore, the powder contains a low proportion of nitro-glycerine, it is necessary to employ in its explosion a correspondingly long, strong, and heavily-charged percussion-cap, made especially for the purpose. For the sake of certainty of explosion it is better to use such a cap in all cases.

If the fire from the fuse comes into contact with the powder before the cap is exploded, which is liable to occur if the fuse is leaky and the cap extends too far into the powder, a portion of the powder will be burned before the explosion takes place. To guard against this, the cap should only be fairly inserted into the powder, and poor fuses wound next to the cap firmly with strong glued paper or hemp, or otherwise secured.

The bore-holes, as a practical but not absolute rule, should be about one-half the size, and the charge should be one-fifth to one-tenth the quantity ordinarily used in gunpowder-blasting.

A very convenient form in which to use the powder is to pack it firmly in cartridges of strong paper.

Having thus described my invention, what I claim is new, and desire to secure by Letters Patent, is —

The composition of matter, made substantially of the ingredients and in the manner and for the purposes set forth.

ALFRED NOBEL

Although the addition of diatomaceous earth to nitroglycerin made the product, dynamite, much safer to use, store, and transport, it was not perfect. It still contained 25% inert material that did not aid in the explosion, and took up space in the mining boreholes, thus making it less powerful than nitroglycerin. In addition, after prolonged storage, some of the nitroglycerin would wick out of the paper cartridges, where it was once again subject to explode by concussion. Both this "sweating" and the inert ingredients were problems Nobel solved in 1875 with his invention of gelignite.

A mixture of guncotton dissolved in ether and alcohol makes a plastic called collodion.  At the time, collodion was used as a wound dressing. Another plastic, celluloid, was made by dissolving guncotton in camphor.

Nobel found that guncotton would dissolve in nitroglycerin. If 7% to 8% guncotton was dissolved in the liquid, the result was a solid jelly that did not sweat, and did not contain any inert ingredients, making it as powerful as liquid nitroglycerin. The resulting gel could be made cheaper by adding sawdust, black powder, nitrates, or chlorates. Nobel finally decided on a mix of the gel with nitrate and sawdust, and called the new product gelignite.

The same method of mixing in cheaper materials such as sawdust and nitrates was applied to dynamite. This is now called dynamite with an active base, and has completely superseded diatomaceous dynamite in the U.S. To keep the mixture from absorbing moisture, fats, waxes, or paraffin are added to the mix.

The pure gel of guncotton dissolved in nitroglycerin Nobel later patented in 1888 as the propellant ballistite, to be used in artillery and small arms. As a smokeless powder, ballistite was an improvement over pure guncotton, and a class of propellants called double-base propellants replaced the (now known as) single-base propellant guncotton. The British invention of the substantially similar cordite led to Nobel suing for patent infringement, but he lost the case in the British House of Lords. Cordite was patented by Frederick Augustus Abel (known for making guncotton practical) and Sir James Dewar, after the two had been evaluating Nobel's ballistite and discussing its manufacture with Nobel.

Guncotton is cellulose nitrated in varying amounts. The more the cellulose molecule is nitrated, the less soluble it is in a 50/50 mix of diethyl ether and alcohol. Nobel thought that the less nitrated form would make a better propellant, as it would be less likely to shatter the gun. Abel and Dewar thought the same, and were surprised to find out that the more highly nitrated form (which was known to be more stable against degrading) was not more powerful, and worked as well in guns as the soluble form. The key to the court case ended up resting on Nobel's patent claiming that the soluble form should be used, and that the insoluble form (which cordite used) was not suitable.