Phosphorus

In 1669 Hennig Brand, a merchant and physician of Hamburg with an interest in the philosopher's stone, reasoned that human urine, being golden, might contain the principle of gold. He collected it in quantity, by some accounts more than a thousand litres, let it putrefy, boiled it down to a syrup and distilled the residue at high heat. What came over and condensed was not gold but a white waxy solid that glowed steadily in the dark without burning, and caught fire on its own in warm air.

He called it cold fire. The name that stuck, phosphorus, is Greek for light-bearer and had previously been a name for the morning star.

This is the first discovery of an element by an identifiable person in a recorded experiment, and it belongs to alchemy rather than to chemistry, which is exactly why it matters here. Brand's method was secret and he sold it; Johann Kunckel and Daniel Kraft acquired it and made money exhibiting the glow at courts across Europe. Robert Boyle, who saw a demonstration, worked out a preparation of his own by 1680 and, unlike the others, published it.

Brand was searching for the wrong thing by reasoning that was wrong, and he found something genuinely new. That is a fair description of a good deal of alchemical practice, and it is a better defence of the tradition than any claim about hidden wisdom.

The glow itself is not combustion. White phosphorus reacts slowly with oxygen at its surface, producing an excited intermediate that emits light, a process now called chemiluminescence. The word phosphorescence, which in modern usage means something different again, took its name from this substance by an accident of history.

Phosphorus does not occur free in nature; it is far too reactive. It is found as phosphate, bound to oxygen, in the mineral apatite and in every living cell.

Its biological role is structural and central. The backbone of DNA and RNA is a chain of alternating sugar and phosphate. Adenosine triphosphate, the molecule that carries usable energy in every organism on Earth, works by making and breaking phosphate bonds. Bone and tooth enamel are calcium phosphate. Cell membranes are built from phospholipids. There is no part of life that runs without it.

That gives phosphate rock a peculiar economic position. Nitrogen fertiliser can be made from the air; potassium is abundant. Phosphorus can only be mined, the workable reserves are concentrated in a small number of countries, and there is no chemical substitute whatever, because nothing else does what phosphorus does inside a cell. Recovering phosphate from waste streams is an active field of engineering for exactly that reason.

The element has several forms. White phosphorus is the one Brand made: waxy, glowing, spontaneously flammable and severely poisonous. Workers in the nineteenth-century match industry, exposed to its fumes, developed phossy jaw, a destruction of the jawbone that contributed to the London matchgirls' strike of 1888 and led eventually to an international prohibition on white phosphorus matches in 1906. Red phosphorus, made by heating the white form, is stable and non-toxic, and is what appears on the striking strip of a modern safety match. Black phosphorus, the densest form, is a semiconductor and has attracted attention as a two-dimensional material.