SILICATES. 



293 



small wire which conducts the boat to the part of the 

 tube, where it should be heated. The tube is then heated 

 to redness and a current of hydrogen passed through it.* 

 When the iron is reduced, the stream of hydrogen is 

 replaced by a current of hydrochloric acid gas, which 

 is continued for an hour or two. Fig. 48 shows the 

 arrangement of this part of the analysis. There may 

 be placed at the extremity of the tube a small flask, in 

 which all volatile materials will condense if any escape 

 from the tube. When the current of hydrochloric acid 



* Fig. 47 represents a convenient apparatus for hydrogen. 

 Fig. 47. 



A and B are two bottles of four or five litres capacity, and tuhn 

 lated at the bottom. By means of a rubber tube E they are united 

 in such away as to put them in communication. The mouth of 

 the bottle B is closed by a cork, which is pierced by a glass tube 

 terminated with the stopcock R. The bottle B is filled with frag- 

 ments of glass to the level of the smaller tube, and a larger part of 

 the space above with zinc. The bottle A is filled with water and 

 hydrochloric acid. By opening the stopcock R, the acidulated 

 water passes to the zinc, and the hydrogen is only given off when 

 the gas is used. 



25* 



