An interesting type of locomotive engine that found very short and limited use in Europe as well as America was the soda locomotive.
The soda locomotive was essentially a steam locomotive, but instead of a furnace to burn coal and heat a boiler, it used a chemical reaction to generate heat.
In a soda locomotive, the boiler was enclosed by a jacket with 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, generating enough heat to boil the water inside the boiler. The steam exiting the boiler was fed through pistons to propel the locomotive, just like a conventional steam locomotive. But in this case, the exhaust steam from the piston was not released into the atmosphere, but returned to be fed to the caustic soda so that the reaction between the caustic soda and water could continue to power the locomotive. Since it was a closed loop system with no exhaust, the soda locomotive ran almost silently. They also did not leave any soot or smoke.
The soda locomotive of the Minneapolis, Lindale and Minnetonka Railways.
A soda locomotive could run for several hours, depending on the amount of caustic soda loaded into the container. Eventually, the baking soda became diluted and did not generate enough heat to continue generating steam. Then the locomotive was delivered to the railway station for “recharging,” which consisted of injecting superheated steam from a stationary boiler at the recharging station through saturated caustic soda to boil off water in solution, leaving solid sodium hydroxide. The soda locomotive was now ready for the next cycle.
The soda engine was invented by Moritz Honigmann, a German chemist and inventor, in early 1880. Soon thereafter, several so-called "fire-free locomotives" were built and successfully used for public transport in Berlin and Aachen. A steamer on the Spree, near Berlin, was also powered by a Honigmann soda engine and successfully sailed up and down the river.
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Around the same time, railways began running soda engines in Philadelphia in the United States.
A detailed study by the Technical College of Munich in 1885 found that the Honigman soda engine is not very efficient as it only produces about 60 percent steam per unit of coal, as traditional locomotives did, although recharging boilers can run on a cheaper, lower quality of coal than boilers on a locomotive. There was also a risk of explosion and scalding of people with hot caustic soda.
In the end, the soda locomotive was not efficient enough, and the danger outweighed any advantage the locomotive had from using caustic soda instead of coal. In any case, the steam locomotives themselves were gradually replaced by diesel and electric engines.