Oddly Powered Clocks>
CORNELIS DREBBEL'S CLOCK: POWERED BY AIR PRESSURE CHANGES
Left: Drebbel's barometric clock: 1610
COX'S BAROMETRIC CLOCK: 1760s
Left: Cox's barometric clock
Cox's clock is still in the Victoria & Albert Museum in London, but I do not know if it is on display; one of these days I mean to go and find out.
HYDROGEN-POWERED CLOCK: 1835
You might think that a hydrogen-powered clock would function by using the gas to run a small internal-combustion engine that would rewind a spring or raise a weight, but a little thought shows that this would be a complicated (and noisy) bit of machinery. Pasquale Andervalt had other ideas...
Left: The hydrogen clock of Pasquale Andervalt
On further thought, what about oxygen as a working fluid? That should be safe enough, unless the concentration in the air becomes high enough to make ordinary materials highly flammable; that seems highly unlikely. So, can we make it by dropping pellets of something into a liquid? One method that suggests itself is dropping pellets of sodium peroxide into ordinary water. This will react "violently or explosively" evolving oxygen and caustic soda, so better make the pellets fairly small. Actually sodium peroxide reacts violently with all sorts of things, and I'm not sure we are heading in the direction of greater safety.
Oxygen can be evolved by dropping manganese dioxide into 6% hydrogen peroxide, but this is a catalytic decomposition and I imagine all of the hydrogen peroxide might decompose at once, bringing back the possibility of an explosion.
Other gases which can be made by dropping solids into liquids are chlorine and sulphur dioxide, but I think the drawbacks there are obvious.
At this point I ran out of innocuous gases, and appealed for anyone with more chemical knowledge than me to suggest a working fluid for this clock that would neither blow you up nor poison you. I received this reply from my correspondent Pigeon:
"In response to your request for comments on possible alternative working fluids:
As a non-serious suggestion: acetylene, from calcium carbide dropped into water. The exhaust is not vented, but stored in a reservoir, and used to feed a little flame so you can still see what time it is at night. (I am presuming that the working pressure does not exceed 1 bar gauge, of course.)
Being serious, though, I would definitely plump for carbon dioxide: unreactive, non-toxic and dead easy to make.
As a suffocation hazard it can be ignored. It is only dangerous in that regard if there is so much of it that it displaces enough oxygen-containing air that you can't profitably breathe the result, which would require a heck of a lot of it. The amount of substance contained in the clock's curly reservoir tube could not possibly produce that much CO2 unless both you and the clock were trapped in a compartment so small that you'd soon breathe all the oxygen in it anyway.
As far as suffocation hazards are concerned, nitrogen is actually worse. Both act purely by displacing breathable air, but CO2 will provide at least some warning that this has happened, because the body determines how hard it needs to breathe principally by detecting excess of CO2, not shortage of oxygen. So excess of CO2 in the atmosphere will cause breathlessness and clue you in that something is wrong (although in practice the effect is small and it still helps to be on the alert for it).
Nitrogen, on the other hand, as one might expect since we breathe 78% of it all the time, produces no warning at all; you just fall over. There was an incident in the King's Cross area when the Victoria line of the Underground was being constructed, due to ingress into the works of air that had percolated down through the clay, losing its oxygen on the way to reactions with reducing minerals and ending up as more or less pure nitrogen. As long as construction was actually in progress there was enough ventilation that this didn't matter, but when operations were paused for the weekend and ventilation ceased, the tunnels filled up with nitrogen. Result was that the first blokes through the door on Monday morning just plain conked out more or less instantly. Fortunately someone following on was sufficiently with it to realise what had happened, so they were able to rescue them in time and without the rescuers suffering the same fate.
And of course CO2 can be produced by the reaction of chemicals so commonplace and harmless that they can be obtained from standard kitchen stock. Vinegar and bicarb will do it. Or vinegar and chalk, for something that conveniently comes as lumps rather than powder.
(Just make sure it's real chalk: blackboard chalk doesn't work, because it isn't chalk, it's gypsum - calcium sulphate. This was a source of disappointment to me at school, when I pinched blackboard chalk out of the classroom and put it into the vinegar pot at dinner, expecting lots of CO2 and a frothy squirty mess... only to find that nothing happened at all. Which continued to puzzle me right up until the internet came along and told me what blackboard chalk really was.)"
At this stage I questioned. I pointed out that there certainly is such a thing as carbon dioxide poisoning, also known as hypercapnia, though a 10% concentration is likely to be needed to kill. However 7% brings on mental confusion. Pigeon replied:
"...Assuming for the sake of argument that a Total Pellet Release Incident generates 100 litres of CO2, to achieve a 10% concentration would require that both you and the clock were shut in a cabinet so small as to leave only 1 cubic metre of unoccupied volume, which would not be a situation you'd willingly get yourself into in the first place. To generate 100 litres of CO2 at STP requires about 400g of calcium carbonate; guesstimating from your photo I'd reckon the capacity of the coiled tube, in terms of pellets of chalk, is of that order, so I still think we're safe."
I am convinced. Carbon dioxide it is.
The clock is currently on display in the Science Museum, London. The clock was presented to the Museum of the Worshipful Company of Clockmakers by William Wing in 1874. The only William Wing known to Google was an entomologist who died in 1855, so the donor is currently mysterious.
Left: The hydrogen clock of Pasquale Andervalt
FRENCH WATER PRESSURE CLOCK
According to Popular Mechanics for April 1914: (p552) "The variations of pressure in the water mains are utilised by a French inventor for the operation of a self-winding clock." And that's all they wrote.
Presumably there was a spring-loaded piston that moved as the water pressure varied with the daily demand cycle; that should provide plenty of power to wind up a clock. Whether it would work with modern water supplies, which one imagines would have good pressure regulation, is another matter.
Google has nothing on this.
THE BEVERLY CLOCK: POWERED BY TEMPERATURE AND AIR PRESSURE CHANGES
The Beverly Clock is displayed in the foyer of the Department of Physics at the University of Otago, Dunedin, New Zealand. It is powered by changes in air pressure, and more importantly temperature, acting on a 1 cubic-foot box of air which presses on a diaphragm and raises the clock weights, presumably by some sort of ratchet mechanism. The clock was built by Arthur Beverly in 1864. The clock has, like the Atmos described below, a torsional pendulum with a very slow period that requires very little power to keep it working; torsional pendulums are used in so-called "400-day" clocks. The Beverly Clock occasionally stops if the ambient temperature has not fluctuated enough.
THERMO-PNEUMATIC CLOCKS: POWERED BY HEAT
The images in this section were very kindly provided by John Howell.
Left: The back of a Puja clock made by the German firm of Jauch and Schmid.
*A remontoire, from the French 'remonter' (to rewind) is a spring or gravity reserve of power that can be configured to give a near-constant driving torque because it is rewound at frequent intervals from another power source- usually this was a mainspring, whose own torque would slowly decrease as it unwound. The idea was that rewinding a spring or lifting a weight at relatively frequent intervals isolated the escapement from the variable torque of the mainspring.
Left: Advertising material for the Puja clock movement.
To save you the trouble of grappling with a German-English dictionary, here are the translations of the salient words in the advert above; "wechselström" means "alternating current", "gleichström" means "direct current", "thermo-aufzug mit glaskolben-laufrad" translates as "thermo-lifter with glass bulb impeller", and "gehwerk" as "movement".
Left: Another Puja clock movement.
THE ATMOS CLOCK: POWERED BY TEMPERATURE AND AIR PRESSURE CHANGES
Anyone interested in oddly-powered clocks will have heard of the Atmos clock, which appears to be mostly powered by changes in temperature, and not, as its name might suggest, solely by changes in atmospheric pressure. A flexible metal capsule is filled with an inert gas and a little ethyl chloride, which vapourises as the temperature rises, causing the bellows to expand, and vice versa. A chain transfers this movement to wind the mainspring. A torsional pendulums with a long period is used to minimise the power required.
Left: An Atmos clock
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