Soda Locomotives

An interesting type of locomotive engine that found very brief and limited use in Europe, as well as in America, was the soda locomotive.

A soda locomotive was essentially a steam locomotive, but instead of a firebox to burn coal and heat the boiler, it used chemical reaction to generate heat.

In a soda locomotive, the boiler was jacketed by a container loaded with several tons of caustic soda, or sodium hydroxide. Water was added to the caustic soda to start a violent exothermic reaction giving off enough heat to boil the water inside the boiler. Steam emanating from the boiler was fed through pistons to propel the locomotive forward, as in a typical steam locomotive. But in this case, the exhaust steam from the piston was not released to the atmosphere, but fed into the caustic soda so that the reaction between the caustic soda and water could continue powering the locomotive. Because it was a closed loop system with no exhaust, a soda locomotive ran virtually silent. They also left no soot or smoke.

A soda locomotive could run for several hours, depending on the amount of caustic soda present in the jacket. Eventually, the soda would become diluted and wouldn't produce enough heat to continue generating steam. The locomotive was then brought to the railway station to be “recharged”, which consist of injecting superheated steam from a stationary boiler at the recharging station through the saturated caustic soda to boil off the water in the solution leaving solid sodium hydroxide. The soda locomotive was now ready for another cycle.

Soda motor of the Minneapolis, Lyndale and Minnetonka Railway

The soda engine was invented by Moritz Honigmann, a German chemist and inventor in the early 1880. Shortly after, several so-called ‘fireless locomotives’ were built and successfully used for public transportation in Berlin and Aachen. A steamer on the River Spree, near Berlin, was also fitted with Honigmann’s soda engine and made successful runs up and down the river.

Around the same time, a railroad began running soda motors in Philadelphia, becoming the first and possibly the only such engines to be used in the United States.

A detailed study conducted by the Technical College of Munich in 1885 found Honigmann’s soda engine not much effective, as it only produced about 60 percent as much steam per unit of coal as traditional locomotives did, although the recharging boilers could be run on cheaper, lower-quality coal than the boilers on the locomotive. There was also the risk of explosion and getting scalded by hot caustic soda.

In the end, the soda locomotive was not efficient enough and the dangers outweighed any advantage the locomotive had of using caustic soda in place of coal. In any case, steam locomotives themselves were being gradually replaced by diesel and electric engines.