124 INTRODUCTION TO GENERAL SCIENCE 



90. THE CHEMICAL ENGINE 



We learned in Section 5, Oxygen, Its Uses and Action, 

 that carbon dioxide bombs are used to extinguish fires. Car- 

 bon dioxide, in solution, is also thrown upon fires in streams, 

 and the force which the streams possess is due to the carbon 

 dioxide. This chemical is produced by the action of an acid 

 upon some carbonate, which is the combination of carbon 

 dioxide and some other element or elements. Where the 

 action is to be slow, marble (calcium carbonate) and sulphuric 

 acid are used. If greater rapidity is desired, sodium carbon- 

 ate or sodium bicarbonate and sulphuric acid are used. 



Chemical engines are of two kinds the small size, which 

 can be carried by a man, and the large size, mounted on a 

 carriage to be drawn by horses. The first style cannot be 

 readily refilled, but the large size is double, and one tank can 

 be recharged while the other tank is in operation. Sodium 

 carbonate is dissolved in the water which fills the tank, and 

 a bottle, arranged to be inverted from the outside of the tank, 

 is filled with sulphuric acid. The tank is then closed, and when 

 a stream is needed, the sulphuric acid bottle is inverted. The 

 chemical action is very sudden, and the engine can be used at 

 once. The pressure of the gas drives out the water with great 

 force. Considerable quantities of carbon dioxide are held in 

 solution. When the water reaches the fire, the chemical is 

 freed and excludes the oxygen from the combustibles. 



References : 



1. 1703 : 192-193. Preparation of Carbon Dioxide. 



a. 1701 : 206. Carbon Dioxide a Fire Extinguisher. 



b. 1704 : 177. Preparation of Carbon Dioxide. 



c. 1706 : 192-195. The Preparation and Properties of Carbon 



Dioxide. 



