6 McDoUGALL AND HOWLES, Nitric Acid from Air. 



gas-tight joint was secured in this, and all succeeding 

 experiments, by the use of a cement composed of a mix- 

 ture of clay, sand, and sodium silicate. This cement sets 

 as hard as stone, and is not easily cracked by sudden 

 variation in temperature, which is important in experi- 

 ments of this nature. 



The electrodes were introduced at A, A', and were 



//-. 2. 



capable of adjustment. A glass tube, C D, conveyed air 

 to the flame. A small plate of glass, E, through which 

 the behaviour of the flame can be observed covers a hole 

 in the slate. At the other end of the vessel, the tube F G 

 conveys the oxides of nitrogen to the condensing appa- 

 ratus. The gases were drawn through the whole system 

 by means of a powerful pump. 



The two large bottles {Fig. 2) were not used during 



