… regardless of whether it was used in agriculture, for preservation, or for cooking, salt was also essential. The human body is constantly losing salt through sweat, and to a certain extent urine, but it tries to keep the blood’s salt concentrations maintained at a certain level. So as the blood loses salt, the body also ejects water to adjust. Ironically, as you lose salt your body responds by drying you out. Without constantly replacing the salt in your body — which is only ever stored for a couple of days at a time — you will at first feel fatigued and a little breathless, but increasingly weak and debilitated, as though sapped of all energy. The slightest exertion would start to bring on cramps, then problems with your heart and lungs, as your body continually shed water. If these did not kill you — and they probably would — you would essentially die through desiccation. The process would be all the faster if you became ill, rendering even the slightest dehydrating fever or bout of diarrhoea utterly lethal.¹

A population deprived of salt was thus one that was weaker and more prone to disease — and at a time when the vast majority of the economy’s energy supply came from the straining of muscle, both human and animal, that weakness in effect meant a severe energy shortage. Although the main fuels for muscle power were carb-heavy grains like wheat, rye, oats, and rice, the indispensable ingredient to getting the most out of these grains was salt — just as how nuclear power uses uranium as its fuel, but also requires a suitable neutron moderator. A population deprived of salt would quite literally be more lethargic and sluggish, making it less productive and poorer too.

Salt’s unique properties made it a serious tool of state. In 1633 king Charles I’s newly-appointed Lord Deputy for Ireland, Baron Wentworth, advised controlling its salt supply as a way to make the Irish utterly economically dependent on England. Given salt was “that which preserves and gives value to all their native staple commodities” — herrings, butter and beef — then “how can they depart from us without nakedness and beggary?” Salt would be a method of control, and a profitable one too, being “of so absolute necessity” that it could be sold to the Irish at inflated prices without much dampening demand: salt “must be had whether they will or no, and may at all times be raised in price”.² Much like economists today, Wentworth saw revenue-raising potential in taxing goods with such unresponsive or “inelastic” demand.

Wentworth’s scheme to control the Irish never came to be. But a great many other countries did choose to tax it. Given a minimum amount of salt had to be consumed by absolutely everyone, monopolising its sale — and levying what was effectively a tax by inflating the price well above the costs of importing or producing it — could function as kind of indirect poll tax, levied more or less per head of both people and livestock, but without any of the administrative hassle of taking and maintaining an accurate census in order to impose such a tax directly.

When compared to other necessities like grain, salt did not need to be traded in especially large quantities either, meaning that its supply could be monopolised with relative ease. And it could not be produced everywhere. Salt tended to be lacking the further you got from the sea coast, unless there happened to be some relatively rare inland sources like salt lakes, brine springs, or rock salt mines. And it could even be lacking on the sea coast where it was either too humid or too cold to get salt cheaply by evaporating seawater using the sun, or where there was insufficient fuel for boiling the brine. These places were thus prone to being charged inflated prices, while the states that controlled places where the costs of production were low — in warmer and drier climes where the salty water of coastal marshes could cheaply be evaporated using only the heat of the summer sun — could extract especially large monopoly profits from the difference. The revenue from controlling solar salt thus became the basis of many kingdoms, some unusually powerful republics, and even empires.

Anton Howes, “The Second Soul”, Age of Invention, 2024-03-08.

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1. Roy Moxham, “Salt Starvation in British India: Consequences of High Salt Taxation in Bengal Presidency, 1765 to 1878”, Economic and Political Weekly 36, no. 25 (2001): p.2270–74.

2. George O’Brien, The Economic History of Ireland in the Seventeenth Century (Maunsel and Company Limited, 1919), p.244, which has the transcription of Wentworth’s proposal