ALLOTROPIC FORMS OF CARBON. 



81 



In order to obtain a spectrum of pure oxygen entirely 

 free from the lines of carbonic oxide, a necessary prelimi- 

 nary condition of our experiment, the following arrange- 

 ment was made. The figure exhibits 

 the form of the tube employed. The 

 part from A to B consists of an 

 ordinary Pliicker^s tube. At the 

 lower end of this a piece of hard 

 glass tubing {d) was sealed. Before 

 the experiment, the requisite quan- 

 tity of permanganate of potash or 

 oxide of mercury was brought into 

 this, to serve as the source of the 

 oxygen, and then the tube was sealed 

 at the lower end. 



The other end of the Pliicker^s 

 tube was closed by a ground-glass 

 stopper (S), through the sides of 

 which two stout platinum wires {pp) 

 were fused, and these were joined 

 together within the tube by a spiral 

 of fine platinum wire [e] , into which 

 the graphite or the diamond was 

 placed. To prevent leakage be- 

 tween the ground sides of the stopper 

 and those of the tube a drop of 

 mercury, rendered less fluid by the 

 immersion in it of a bit of tin foil, 

 was introduced into the joint. The 

 tube was placed in connexion with 

 the air-pump by means of a side 

 tube sealed on at (C). For this 

 purpose a Sprengel pump was used, 

 to which the side tube was herme- 



SER- III. VOL. VII. 



