Savery's Miner's Friend

Never seal a vessel that is being heated. Everything here is either open to atmosphere or removed from the heat before it is closed. Steam scalds worse than boiling water because it gives up its latent heat on your skin.

Fit a 250 ml borosilicate flask with a stopper carrying one glass or steel tube long enough to reach well below the water in a bowl. This flask is Savery's working vessel.

Put 30 ml of water in the flask and boil it with the stopper off until steam has been streaming out for a full minute. The point is to drive the air out and leave the flask full of steam.

Remove the flask from the heat first, then fit the stopper and put the free end of the tube under the water in the bowl. Order matters: heat off, then close.

Wet the outside of the flask with a cold cloth. The steam condenses, the pressure inside collapses, and atmospheric pressure drives water up the tube into the flask. Nothing pulls it — the outside air pushes.

Measure the volume drawn in and the height it climbed. Write both down: that volume times that height is the useful work one condensation stroke did.

Run it again but let the flask cool in still air instead of with a cloth. It lifts the same water far more slowly. Savery's engines had their outsides doused with cold water for exactly this reason — condensation rate sets the cycle time.

Atmospheric pressure supports a column of water about 10.3 m high at sea level, and a real system with an imperfect vacuum and friction manages far less. Calculate it, then note what it means: the suction stroke alone could never empty a deep mine.

Sketch the full engine: a boiler, two working vessels and taps between them. While one vessel is condensing and drawing water up, the other is receiving steam and forcing its water out. Alternating them gives something close to continuous delivery.

Write out the four positions of the taps in order: steam to vessel, steam shut and vessel cooled, water drawn up, steam readmitted to force it out. The engine has no other moving parts, so this list is the entire machine.

On the sketch, mark the boiler and the forcing vessel. These are the parts that had to hold pressure, in an age of soldered seams and no reliable safety valve — and they are the reason the real machine is documented here rather than built.

1698, and a very broad patent. Thomas Savery patented his engine for "raising water by the impellent force of fire" in 1698 and published The Miner's Friend setting out its use. Parliament later extended the patent's life by statute, and its wording was wide enough to cover essentially any engine raising water by fire. That single legal fact shaped British engine building for a generation.

Newcomen worked under it. Thomas Newcomen's atmospheric engine of 1712 is a different and far better machine — it has a piston, a beam, and separates the water being pumped from the steam doing the work — but it fell inside Savery's patent, so Newcomen never held a patent of his own and worked in partnership with the Savery interest. The commonly repeated "Newcomen's patent" is a myth, and it is worth correcting whenever the story is told.

Why the Miner's Friend was a poor friend to miners. The suction stroke is capped by atmospheric pressure at around ten metres in theory and less in practice. Anything deeper had to be lifted by steam pressure directly on the water surface, which meant boiler pressures the metallurgy of 1700 could not safely hold. Savery engines burst. They were also thermally wasteful, because every cycle heated and cooled the same vessel. They found real use pumping water in waterworks and on a modest scale, not clearing deep mines.

What it contributed anyway. Savery's machine is the first steam engine sold as a product rather than demonstrated as a curiosity, and it established the central move that the whole eighteenth century built on: condense steam, get a vacuum, let the atmosphere do the work. Newcomen put a piston in that vacuum. Watt then noticed that condensing in the working cylinder wastes most of the heat, and put the condenser somewhere else. Each step is a direct answer to a flaw in the one before, and the chain starts here.