II. RESEARCH. 



575 



about half an inch m diameter and graduated in millimetres. This tube I 

 shall speak of as the pressure tube. The cylinder a and the pressure tube <j 

 are thus in permanent connexion, and constitute one vessel, which is broken 

 into parts solely for facility of construction. This apparatus is supported 

 upon three .screws, as shown in the figure, by the adjustment of which the 

 pressure tube g is placed in a perpendicular position before the commence- 

 ment of the experiment. The steel stopcock k is a three-way stopcock, in 

 which the channels are so cut that a communication may be made between 

 the tube / and the cylinder , or between the tube m and the cylinder a, or 

 between the tubes I and m (all other communications being shut off) at 

 pleasure ; or the communications may be entirely closed. 



In the cylinder a is placed a thin piece of glass rod, to which seven points 

 are attached, also of glass, as shown in the figure. The capacity of the 

 cylinder a between each point is ascertained by calibration with mercury. 



The cylinder and pressure tube are enclosed in a second glass cylinder n 

 filled with water, in which a thermometer is placed. 



For further detail as to the construction, calibration, and mode of operating 

 with the apparatus, see Phil. Trans., 1872, p. 3. 



In Fig. 5 a drawing is given of the whole apparatus as arranged for 

 experiment. 



Fie .5. 



2 4:0 9 a. Apparatus by which the body in the atmosphere which 

 acts upon Schonbein's test-papers was first certainly proved to 

 be identical with ozone. Dr. Andrews, F.R.S- 



Atmospheric air, in fine weather and acting freely upon the test-papers, was? 

 drawn steadily through a glass globe, capable of being heated to 300 C., 

 when all chemical reactions disappeared, which could only occur in the case 

 of ozone. 



