CHAPTER XI 



HYDROCHLORIC ACID. CALCULATIONS 



THUS far, the substances we have studied have been mainly 

 air and its components and water and its constituents. Another 

 of the simpler, familiar substances, common salt or sodium chloride 

 (Nad) may now be taken up. Large amounts of it are used in 

 the household, in cooking and in making freezing mixtures. Still 

 larger quantities are consumed in manufacturing washing soda 

 and soap, for both of which it supplies the necessary sodium. It 

 is employed also to furnish the chlorine for bleaching materials. 

 We shall consider it first as a means of making compounds of 

 chlorine. 



Preparation of Hydrogen Chloride. When a few drops 

 of commercial, concentrated sulphuric acid (H 2 SO 4 ) are poured 

 upon common salt in an open dish, vigorous effervescence begins. 

 This indicates that a gas is forming bubbles upon the salt and 

 that the bubbles are rising through the layer of acid and burst- 

 ing. The gas is itself invisible, but when we breathe upon the 

 contents of the vessel, a heavy fog is produced. This is due to 

 condensation of water vapor (in the breath) to droplets of water, 

 in which the gas has dissolved. The fog is composed, in fact, 

 of drops of a solution of hydrogen chloride (HC1) in water, which 

 receives the name of hydrochloric acid (in commerce, muriatic 

 acid). 



In order to handle the gas more readily, the sulphuric acid 

 may be allowed to fall from a funnel, drop by drop, upon salt con- 

 tained in a flask (Fig. 47). Soon the air in the flask is all dis- 

 placed by the gas, and the latter issues from the open delivery 

 tube. If a U-tube containing some water is attached to the 



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