An account of a useful discovery to distill double the usual quantity of sea-water, by blowing showers of air up through the distilling liquor

In Short

This practical scientific treatise details an ingenious invention for doubling the quantity of fresh water obtained by distilling sea-water using minimal fuel, while simultaneously introducing mechanical ventilators to clear foul air from crowded ship holds. Through rigorous experiments, the author demonstrates how bubbling air through heated liquids not only extracts pure drinking water and purifies stinking liquids, but also expels the deadly, pestilential vapours responsible for rampant mortality in maritime and transport vessels. It endures as a masterclass in empirical observation aimed entirely at alleviating human suffering.

The Story

The work opens with a pressing maritime crisis: the desperate scarcity of fresh drinking water on long voyages and the staggering human toll exacted by foul, stagnant air trapped within crowded ships. Reviewing past, inadequate attempts to render sea-water potable—which always demanded prohibitive quantities of fuel and yielded meager results—the text introduces a breakthrough inspired by a model designed to raise water by fire. By attaching double bellows to convey streams of fresh air upward through boiling sea-water, the process dramatically increases vapor output, allowing a small still to produce double its usual volume of fresh water with half the fuel.

The narrative progression then expands from distillation to the broader mechanics of purification and health. The author meticulously details how to construct, weight, and connect the double bellows using leathern pipes, bamboo canes, or wooden tubes, ensuring a steady stream of air despite the rolling motion of a ship. Through careful trial and measurement, utilizing graduated glasses and floating pewter indicators, the text establishes exact proportions for stills of various sizes, proving that ventilation prevents the violent overflowing ebullition common in traditional boiling.

To ensure the distilled water is wholesome, the text investigates various chemical additions meant to neutralize the bitter salts and bituminous elements of the sea. Moving beyond Appleby’s expensive compounds and quicklime, the author discovers that simple, inexpensive powdered chalk—used in small proportions—effectively fixes the noxious spirits and leaves the water sweet, clean, and capable of lathering soap and boiling peas. Verification tests using silver and mercury solutions confirm that the resulting water contains negligible traces of salt spirit.

From the galley stove, the argument extends into the oppressive depths of transport vessels and slave ships, where confined air and poor provisions foster fatal distempers like the scurvy and the jail-distemper. Eyewitness accounts from sea captains and doctors document how mechanical ventilators cool and dry the interior spaces, dramatically reducing mortality rates among passengers and crews alike. The narrative broadens further into domestic and natural trials, demonstrating that blowing showers of air through heated milk successfully eradicates the rancid tastes caused by turnips and cabbages, sweetens putrid well-waters, and prolongs the vitality of fish in restricted pails.

The work culminates in an impassioned moral appeal against the twin destroyers of human life: pestilential air and the immoderate consumption of spirituous liquors. Urging society to abandon its indifferent tolerance toward preventable maritime catastrophes, the author frames the adoption of ventilators and fresh water not merely as technical improvements, but as an urgent moral duty essential to preserving the dignity and lives of thousands.

How It Unfolds

The search for fresh water The text establishes the critical need for ample drinking water on voyages and details how an accidental observation involving a model engine inspired the revolutionary method of blowing air through boiling liquids. This technique overcomes previous failures by drastically reducing fuel consumption while doubling distillation output.

Mechanics of the ventilation still Detailed instructions explain the assembly of double bellows weighted with lead plates to match the pressure of varying liquid depths. Flexible pipes channel the air from the deck-mounted bellows directly into the lower chambers of the stove-fixed stills.

Ensuring purity and taste Various chemical agents, including lime, soap-lees, and powdered chalk, are tested to neutralize the bitter oils and salt spirits inherent in sea-water. Powdered chalk emerges as the superior, cost-effective additive, verified through chemical tests with silver solutions to yield clean, wholesome water.

Transforming shipboard health Expanding beyond the galley, the text compiles compelling reports from captains detailing how deck ventilators eliminate stagnant, pestilential air in crowded transport and slave ships. These devices maintain cool, dry conditions that dramatically slash mortality rates and protect crews from putrid distempers.

Sweetening milk and water Experiments demonstrate that upward streams of air successfully eradicate the rancid tastes imparted to cow milk by turnip and cabbage diets. Similar ventilation rapidly restores sweetness to foul-smelling well-waters and stagnant sea samples.

A final moral crusade The work concludes with a passionate plea for humanity to cast aside ignorance and prejudice regarding public health measures. It urges readers to embrace simple technologies that prevent the needless destruction of millions of lives.

The People

Stephen Hales stands as the central intellectual figure of the work, driven by an unwavering desire to alleviate human suffering and preserve the lives of sailors and travellers. He faces obstacles of widespread ignorance, technical skepticism, and the sheer inertia of human prejudice. Through relentless experimentation, he emerges as a successful innovator who provides concrete, life-saving solutions.

Mr. William Baily appears as an ingenious craftsman who shares his model for raising water by fire, sparking Hales’s breakthrough realization about increasing vapor output. Captain Henry Ellis wants to promote the public good at sea, battling the stubborn resistance of traditionalists; equipped with ventilators, he succeeds remarkably, completing a long voyage with zero crew fatalities and minimal loss among his passengers.

Dr. Butler and Mr. Appleby appear as contemporary investigators seeking methods to produce fresh water through chemical additives and soap-lees, though their proprietary or complex methods are ultimately refined or superseded by Hales’s simpler chalk techniques. Mr. Shipley facilitates the initial collaboration between Hales and Baily, bridging the worlds of formal science and practical arts. Finally, the anonymous sailors, enslaved persons, and transport passengers want basic health and survival, standing against the invisible perils of putrid air and rancid water; where ventilation is applied, they emerge transformed from victims of inevitable maritime pestilence into healthy survivors of arduous journeys.

In Its Own Voice

Illustrating the core innovation of the treatise, the author describes the surprising outcome of his initial comparative trials:

Where I found, to my Surprise, that sometimes three times more was distilled by Ventilation than by the usual Way...

Addressing the widespread neglect of life-saving equipment aboard vessels, Captain Henry Ellis remarks on the psychological barriers encountered at sea:

The Vis-inertiæ of Mankind is not the only Difficulty you have had to encounter, but their Ignorance and Prejudices, which are almost insuperable.

Reflecting on the staggering human cost of neglected shipboard hygiene, the author issues a powerful ethical challenge to his readers:

Was there ever a more important Occasion to rouse the Indignation of Mankind?

What It's Really About

At its heart, the book explores the intersection of empirical science and human ethics, arguing that technological negligence is a moral failure. It investigates how stagnant environments—whether the foul air of a crowded ship hold or the putrid rot of unventilated water—actively promote physical decay and moral degradation. The underlying question challenges society's callous acceptance of mass mortality, asking why humanity remains indifferent to preventable suffering when simple mechanical interventions like bellows and ventilators are readily available. By linking physical respiration and distillation directly to the purity of the human blood, the text frames cleanliness not merely as a matter of comfort, but as an absolute prerequisite for civilized existence and the preservation of human life.

Why Read It Today

Readers fascinated by the history of science, maritime history, and early industrial ingenuity will find this work utterly captivating. Reading it feels like looking directly over the shoulder of an Enlightenment philosopher as he tinkers with tin vessels, double bellows, and chemical reagents in his workshop. One experiences the genuine thrill of empirical discovery, where every experiment—whether testing chalk proportions or reviving sluggish fish—serves a profoundly practical end.

However, contemporary readers must navigate the period’s stark realities, including the matter-of-fact documentation of the eighteenth-century slave trade and the dense, technical prose of mid-eighteenth-century scientific reporting. The archaic spellings, long digressions, and unvarnished language of the era require patience. Yet what stays with you long after closing the book is the author's profound moral urgency—his fierce, uncompromising indignation at preventable human loss. His voice serves as a timeless reminder that scientific inquiry achieves its highest calling when dedicated entirely to the preservation of human dignity and life.