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Wednesday, 5 August 2015

The caustic bite of alkali

Most of the words beginning with al-, scientific and mathematical terms like algebra and alcohol, come to us from Arabic, where the 'al' part is the equivalent of 'the' in English. Alkali in Arabic is al kali, otherwise known to us as wood ash, high in potassium, and mainly used to make soap, when it is added to rendered fat.

The wood ash was made in 19th century Britain by heating wood in a clay pot, hence it went by the name pot ash. When Humphry Davy made a metal by electrolysis from a preparation of pot ash or potash, he Latinised its name as potassium, but then came a problem.

The element could not have the symbol P, because that letter had already been used for phosphorus. So by looking backwards, a new Latin name was created: kalium, and that allowed the chemists to identify potassium, derived from potash by the symbol K, reminding us of the Arabic al kali.

Chlorine-caustic soda works, Wikimedia
Alkalis of various sorts were important in the early 19th century, as industry began to grow. Originally, textiles were bleached with ammonia derived from stale urine, and stale milk, which was acidic, but as the industries scaled up, there was no longer enough urine to go around, though the acid was replaced after about 1750 by dilute sulfuric acid.

Just as importantly, cloth then needed to be expose to sunlight over several weeks, and that tied up valuable agricultural land, and the cloth was likely to be stolen. So factory owners were keen to make stronger bleaching chemicals.

By 1800, 'alkali' was an essential raw material for making paper, glass, and soap, and in bleaching and dyeing. The alkali known as 'soda' (more recently soda ash) was usually obtained from the barilla plant found around the Mediterranean, or from burning kelp plants, but early industrial chemistry was pushed along tremendously by the need to make these chemicals more efficiently.

Quality was also a problem, and by 1806, French chemists were using an instrument like a burette, called an alkalimeter, in order to measure the strength of the alkalis produced. Like the Germans in the First World war, the French found themselves restricted by a British naval blockade.

This stopped them accessing American sources of potash during the Napoleonic wars, and so research continued — leading, in passing, to the accidental discovery of iodine when Bernard Courtois was working with ash from seaweed to make saltpetre.

He later passed this information on to Sir Humphry Davy, who proposed the name "iodine", from the Greek word for the colour violet, iodes, just a moment he took off from discovering the alkali metals.

During the 19th century, and into the 20th century, the 'alkali town' existed as a sort of hell on earth, where smoke, acid fumes, chlorine and other gases filled the air and attacked the lungs of residents. The products, said one critic, were " . . . pills, coal, glass, chemicals, cripples, millionaires and paupers." To that, we might add corpses and a strong chemical industry.

The ancient Egyptians used alkali, which they called natron or natrium, depending on whether you consult a Greek or a Roman source, and the name tells us straight away that this was a soda ash, or impure sodium carbonate. 

Sodium, when Davy discovered it, could not be represented by the symbol S, which was already being used for sulfur. So he turned to the Latin and Greek name for the source, realised that N had been used for nitrogen, and that is how sodium gained the symbol Na.

One major source for the natron, which the Egyptians used in mummifying, was a set of lakes to the south of Egypt, including, perhaps, Lake Natron, near the border between Kenya and Tanzania, south-west of Nairobi.

Today, this lake is famous mainly for the flamingoes that live there, but it seems a little distant to be the source of all the natron that was needed by the Egyptian undertakers. Certainly we know that the natron came from a lake, because this is clearly stated in The Book of the Dead, but the actual lake involved is still a matter for conjecture.

If Pliny is to be believed, the transport of natron had an even bigger effect, but to recognise this, we have to know that 'nitre' and 'nitron' were also acceptable names for this material, even though it contains no nitrogen at all. Here is Pliny in a translation by Philemon Holland in the early 17th century:

"The coast along this river which showeth this kind of sand, is not above half a mile in all, and yet for many a hundred year it hath furnished all places with matter sufficient to make glass. As touching which device, the common voice and fame runneth, that there arrived sometimes certain merchants in a ship laden with nitre, in the mouth of this river, and being landed, minded to seethe their victuals upon the shore and the very sands: but for that they wanted other stones to serve as trivets to bear up their pans and cauldrons over the fire, they made shift with certain pieces of sal-nitre out of the ship, to support the said pans, and so made the fire underneath: which being once afire among the sand and gravel of the shore, they might perceive a certain clear liquor run from under the fire in very streams, and hereupon they say came the first invention of making glass."

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