166 CHEMISTRY. 



of turpentine, which is composed of carbon and hydrogen, 

 and put it into a jar of chlorine, it will burn spontaneously 

 (Fig. 69, p. 165), the hydrogen making the flame, and the re- 

 leased carbon producing a cloud of heavy smoke. 



222. Hydrochloric Acid, HC1. We have already had so 

 much to do with this acid that you know its composition 

 and nature. We have hitherto always used a solution of 

 gaseous hydrochloric acid in water without further expla- 

 nation. Hydrochloric acid, then, is a colorless gas, with acid 

 properties, pungent odor, and very soluble in water ; in fact, 

 water is capable of taking up 500 times its bulk of this gas. 

 Commercially this solution is called muriatic acid a name 

 a hundred years old. Hydrochloric acid dissolves many 

 metals, forming chlorides. It is of great value in the arts. 



223. Production of Hydrochloric Acid. It can be pro- 

 duced synthetically, i. e. y by the direct combination of its 

 elements, and it is curious that light is the agent that makes 

 them combine. If equal quantities in bulk be mixed by 

 candle-light, and be kept in the dark, no combination will 

 take place, but the two gases will remain simply mixed to- 

 gether. If now the jar containing the gases be exposed to 

 the direct rays of the sun, the union will be so sudden as to 

 cause an explosion. Sometimes this result occurs by expos- 

 ure to the diffuse light of the sun, but commonly the di- 

 rect rays are required. Of course in this very dangerous 

 experiment the jar should be inclosed in a wire screen to 

 guard against injury. 



224. Common Mode of Preparation. Hydrochloric acid is 

 commonly prepared by mixing together common salt and 

 dilute sulphuric acid, and applying heat to the mixture. 

 The chemical reaction is as follows : 



Sodium Sulphuric Hydro-sodium Hydrochloric 



chloride. acid. sulphate. acid gas. 



NaCl + H 2 S0 4 = NaHS0 4 + HC1 



