Little Known Facts: The Engine that Ran on Baking Soda

Today is the 200th anniversary of the birth of Zach Leigh-Wright, inventor of the Airey Engine.

Leigh-Wright, a nephew of Lancashire brewer Isiah Wright, invented the Airey - the name is derived from its full title, the Acid/Alkali Alternating Impulse Reaction Engine (AAAIRE) - in an inspired act of social philanthropy.

In the mid C19th the Crimean War required widespread requisition of horses for combat and to draw guns. One effect of this was a shortage of dray horses. This led in 1854 to the infamous 'Winter of the Mares', when women (and even children), mostly from brewery workers' families, were employed to pull the brewer's wagons in northern towns. Moved by their plight, Leigh-Wright realised that vinegar - a by-product of the brewing process - might be used to power the drays.

Leigh-Wright's invention bore some similarity to Hero's 1st century steam-powered 'Aeolipile', although there is no evidence that Zach was aware of the Aeolipile or influenced by it. At its simplest the Airey engine consisted of an oscillating drum internally divided into two 'tadpole-shaped' chambers, similar in cross-section to the Taoist 'Taijitu' or yin yang symbol. Pressurised aerosol sprays of sodium bicarbonate (baking soda) and atomised aqueous acetic acid (vinegar) were injected alternately into the two chambers through jets in a central axle. The result was chain of a rapid exothermic reactions producing CO2 gas and a massive expansion in volume (a reaction familiar to children who have made papier maché 'volcanoes' in their kitchens at home).

The expanding gases were ejected through nozzles at the narrow end of each chamber, causing the drum to rotate in alternate directions. The oscillation was governed by an escapement, and converted into rotational movement via a camshaft.

Airey-powered drays were a familiar sight, sound and scent around the streets of Preston, Leeds, and Bradford in the mid 1850s, but the engine had several drawbacks; it emitted large quantities of water, there were appalling corrosion problems, and the expansion chambers tended to become clogged with residue. Ironically, the mechanical drays were also unpopular with the brewer's men, who had found the employment of their wives to haul wagons a useful source of extra income.

In the following decade the increased availability of heavy horses and improvements to the steam engine gradually eclipsed the Airey engine, and by the 1870s the internal combustion engine was beginning its inexorable ascendency.

Although today it is all but forgotten, the non-polluting technology of the Airey engine may yet see its return, especially as new technologies now enable baking soda to be produced from carbon retrieved from furnace gases, making the operation of the engines carbon neutral.