plate, and, together with the plate, is removed in the same 

 manner as it was applied. The mouth of the jar is turned 

 upwards, the plate removed, and the gas submitted to exa- 

 mination: or, with mouth downwards, the small jar is placed 

 on the slxclf of the pneumatic trough, as the experiment may 

 require. This detail appears tedious, but the practice is very 

 easy. I^n this process there is, however, some danger of dis- 

 turbing the lower plate, by lifting it from the mouth of the 

 inagazine jar, and so vitiating the gas by the introduction 

 of common air. To prevent this inconvenience, it is neces- 

 sary to secure the two perforated plates to the mouth of the 

 jar, and to each other, allowing the upper plate, at the same 

 time, tOj slide freely over the other. For this purpose, it is 

 necessary to fix the plates, and the magazine jar, in a frame; 

 wliich renders the use of them very convenient, and not 

 liable to accidental diBtmbance. 



The two plates (a and b), as in Fig. 1., are fixed in the 

 upper part of the frame : (a) is fastened, (b) slides easily over 

 it. The jar (d) is pressed up against the plate (a), by a 

 moveable bottom (k), tightened by wedges or screws. The 

 jar may be filled with water before it is fixed in the frame, 

 and inverted in the trough; or the air may be generated in 

 the jai", without the ; frame, and then, the frame being in- 

 xerjbed^ and the plates sunk in the water, the jar may be 

 slipped into its place, and fixed there, which is the better 

 way. The frame and jar are then set upright, and the gas 

 may be transferred 9.$,, before, without danger of loss or 

 mixture. ; ' ,]■' 



By 



