Armstrong's Electrostatic Boiler.

Updated: 4 April 2005
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The steam boiler as a means of generating static elecricity is not an obvious concept. It was developed by William George Armstrong, (1810-1900) allegedly as a consequence of an incident with a colliery boiler: "A mechanic was busy repairing a steam-engine near Newcastle, having one hand in a jet of steam that was escaping from a leak, with the other hand on the lever of the safety valve; he drew a brilliant spark and received a violent shock. Armstrong studied the conditions of the phenomenon."
Armstrong built his first electrostatic boiler in 1842. he went on to establish the famous Armstrong armaments company at Elswick, and it is for this he is best known.

The quoted details here are taken from "Electricity and Magnetism" edited by Silvanus P Thompson, pub Macmillan 1891.

"There was one at the Polytechnic in London with forty-six jets, and which gave sparks two feet long; that at the Sorbonne, in Paris, has eighty jets, and gives sparks several inches in length."

Investigations by Michael Faraday proved that escaping was steam was not sufficient to generate electricity; it had to be wet steam, partially condensed and so carrying water droplets with it. Armstrong's boiler therefore has a rectangular box cooled by water to produce some condensation. The theory was that the water droplets became electrically charged due to friction with the wooden walls of the boxwood nozzles; however it appears that even today there is no consensus on the exact mechanism. This is not just an academic question as in 1969, three large oil tankers were sunk or damaged by explosions thought to be caused by sparks from electrically charged mist during tank washing with jets of hot and cold water or steam See here (External link)

Left: The Armstrong Electrostatic Boiler

The boiler is insulated from ground by four glass legs. Steam jets escape from boxwood nozzles on the rectangular cooler box. The stand to the right, apparently incorporating a glass column, collects the electric charge by a series of sharp metal points held opposite the jets. This version appears to have three nozzles.

Going from left to right along the top of the boiler, can be seen the pressure-gauge (which appears to be some sort of mercury manometer) the steam-dome and control-valve, with the cooler box on top, and a lever-type weighted safety-valve. On the side of the boiler is a water-gauge of the usual sort.

The small curved pipe running from the cooler box to the chimney is of unknown function; possibly it carried away steam evolved from the cooling water.

The operator appears to be adjusting the steam-valve; how he could do this without getting a severe shock is not clear. Even if the valve handle was insulated, this would not stop a voltage that could throw two-foot sparks.

One wonders if the square-jawed chap at the valve is supposed to be Armstrong himself: see portrait below.

Left: William George Armstrong, about 1870.

Left: One of the boxwood nozzles in section.

Note the deliberately indirect steam path. Quite what this had to do with charging the steam is at present obscure.

There is an Armstrong boiler in the Museum of The History of Science at Florence; for all I know it is the only one in the world, though there may be one at the l'École Polytechnique near Paris.
Unfortunately photography is not permitted in the Florence museum, so I am unable to show you the pictures below:

Left: Armstrong Electrostatic Boiler at the Florence Science Museum.

This machine was made by Watkins & Hill of London, around 1845. It is missing a few parts, but otherwise closely resembles the contemporary drawing above. This one has four steam nozzles.

Missing are the four glass legs, the chimney, the safety-valve, the pressure-gauge, and the glass tube of the water-gauge.

The boiler is about a meter long. The museum gives its dimensions as 855x408 mm.

Left: Armstrong Electrostatic Boiler at the Florence Science Museum.

The Florence boiler has some kind of triple valve arrangement not shown in the drawing at the top of the page. Its function is unknown.

While the Armstrong boilers were considered to be the most powerful electrostatic machines of their day, there were problems. In operation they inevitably filled the room with steam, producing a humid environment hardly suitable for electrostatic experiments which depend on dryness to maintain insulation.
One also wonders how the machine could be fuelled while in operation without giving the stoker a severe shock; possibly the boiler would be grounded while this was done.

The Armstrong boiler was not the only method of tackling the apparently paradoxical task of generating static electricity with water; another was Kelvin's Water Dropper. (which I think might well be calling out for a web page)

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