47 
made. Fig. 1 exhibits the form of the tube i 
employed, The part from A to B consists 
of an ordinary Plucker’s tube. At the | 
lower end of this a piece of hard glass 
tubing (a) was sealed. Before the experi- 
ment, the requisite quantity of permanga- 
nate of potash or oxide of mercury was 
brought into this to serve as the source of 1 
the oxygen, and then the tube was sealed 
at the lower end. 
The other end of the Plucker’s tube 
was closed by a ground glass stopper (S), 
through the sides of which two stout 
platinum wires 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 between 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 connection 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 hermetically sealed. In this way and 
in this way only was it found possible to 
obtain a pure spectrum of oxygen. After 
the connection with the pump had been made, the whole 
tube was exhausted, and then the substance contained in the 
hard glass tube was heated. The oxygen which is given off 
was then removed by the pump, the tube filled a second 
time with oxygen, this again removed, and this process 
repeated over and over again, until at last no other lines 
but those of oxygen are seen, when the spark from an 
induction coil passes betweenThe electrodes {g and h). 
