The carbon dioxide of the mixed gases of combustion unites with the carbonate and forms bicarbonate, though the interchange is far from complete. Some of the carbon dioxide escapes unabsorbed and some of the carbonate is un converted to bicarbonate.
The solution issuing from the towers, con taining bicarbonate, is now pumped through suitable heat exchangers to the lye boiler. This may either be heated by the coke fire which served to produce the gases or by exhaust steam from the engine and compressor. In the latter case the coke is burned under the steam boiler.
By boiling the bicarbonate solution, it is reconverted to carbonate and the released car bon dioxide is piped through heat exchangers and coolers to the gasometer.
Final preparation for the market consists in liquefying the gas in compressors operating in per square inch and storing it in steel cylinders holding either 20 or 50 pounds of the gas.
Commercial Uses of Carbon Dioxide.— The larger portion of commercial carbon dioxide is used in the manufacture of car bonated beverages. It is also used in refriger
ating machines, especially in connection with marine work. It is used for spraying paint and insecticides and is the active reagent in many fire extinguishers.
Medicinal Uses.— When liquefied carbon dioxide is allowed to expand rapidly a very low temperature is produced with the resultant formation of solid carbon dioxide. This may be collected in snow-like form and has been found efficacious as a local application where the removal of warts or wens is desired.
The gas as such or dissolved in saline water has marked therapeutic effects. The carbonated baths of Bad-Nauheim have a world-wide reputation and numerous other resorts are now Snipped to give the Nauheim bath treatment. The effect of immersion in such baths is to stimulate the circulation and to reduce the pres sure on an overloaded heart. The action of the gas is undoubtedly reflex. Remarkable re sults are obtained as well with rheumatic and neurasthenic cases as with cardiac ones.