LIQUIDS AND ALUED EXPERIMENTS. 



47 



33. Apparatus. — The construction of the apparatus is shown in fig. 15 

 in vertical section. Here//'/'/ is an inverted bell jar, with a ground edge at 

 // and a neck for a stopper at /'/'. This is closed with a brass lid, ee, and 

 contains the charge of paraffin oil as far as the level ww. The plates of the 

 condenser are shown at gg and hssh, hh being the guard ring and w the 

 movable disk. In order that hssh may be nearly plane the inner circular 

 edge of hh is turned as thin as possible (not shown). The plate gg is held 

 by a rod aa (with a clamp screw on top), the latter fitting snugly into the 

 hard-rubber cylinder, to which it may be fastened with a set screw. The 

 cylinder bb is in turn held by a sleeve and set 

 screw, axially and vertically at the center of 

 the lid ee. Hence gg may be adjustably raised 

 by any desirable amount, or lowered into 

 contact with hh. 



In another form of the apparatus the rod 

 aa, holding the disk, may be replaced by a 

 micrometer screw and stuffing box. 



The disk, ss, is floated on the Cartesian 

 diver k of very thin brass tubing, to which it 

 is soldered. The level of the liquid within 

 is shown at v. Four adjustable bent wires 11 

 keep the float in position, concentric with 

 the axis of the circular plates of the condenser, 

 and also prevent its falling below a conve- 

 nient level. 



The guard ring hh is supported by four 

 strips of copper nn snugly fitting the inside 

 of the bell jar. These are braced by a ring 

 of metal mm, to which the strips nn are sol- 

 dered. They terminate at the top of the 

 tube pp, which is the lower electrode of the 

 condenser, the clamp being at r. The tube 

 pp finally is held in place by the perforated 

 cork qq, all parts fitting tightly. In a fur- 

 ther improvement of this apparatus, the guard ring is adjustable, being 

 placed on three leveling screws, respectively, rotating with three springs. 

 The wires 11 are also adjustable. 



The lid, finally, is provided with the tubulure c in connection with the 

 exhaust pump and a stop-cock d for the introduction of air, the tube p 

 below being closed by a cock (not shown) when the apparatus is used. 



The apparatus as a whole is held in a suitable standard, and the ground 

 edge of the lid ee is clamped securely (air-tight) to the ground top of ff. 

 All other joints are made air-tight by an appropriate cement, applied on 

 the outside. 



To adjust the apparatus it is first filled with oil, through pp, to the 

 required level, the bell jar being placed neck upward for the purpose and 



Fig. 15. — Absolute electrometer 

 with disk carried on Cartesian 

 diver. 



