GENERAL APPARATUS AND MANIPULATION 183 



arrangement shown in Figure 68. An electric circulation pump (P) 

 sends a current of air, divided by the T-tube (a), into the chamber. 

 The water in the large bottle (B) is warmed by a lamp (about 40 

 watt) to a temperature 5° higher than that of the room, and the 

 copper coil attached to the arm (6) is surrounded with water cooled 

 5° below the room temperature. The air passing into the water in 

 (B) is dispersed into fine bubbles. The currents of warm and cool 

 air enter the chamber at the same corner and the baffle (d) permits 

 them to mix without allowing water droplets to be carried into the 

 center of the box. The box contains a thermometer (/) and a hair 

 hygrometer (e) fitted with an electrical contact at the percentage of 

 moisture desired. By means of pinch cocks on tubes g and b, the 

 warm air stream is first regulated so that the temperature rise in 

 the chamber is about 1° in 15 min. when the cool air is shut off, and 

 then sufficient cool air is admitted to compensate for this tempera- 

 ture rise. The contact on the hygrometer is connected through a relay 

 to the pump which automatically stops when the desired humidity 

 is attained and starts when it begins to fall. A thermoelectric control 

 of the air flow through a or 6 could be used to achieve finer regula- 

 tion, but Holter found it unnecessary for his work. 



G. ELECTRODES 



Linderstr^m-Lang, Palmer, and Holter Silver Electrode. A 



simple electrode arrangement (Fig. 69) was used by Linderstr0m- 

 Lang, Palmer, and Holter (1935) for the micro determination of 

 chloride by electrometric titration. The silver wire electrodes (A) 

 and (^4') are employed as shown. A is fixed with a bit of picein in 

 the side tube of the tip of the burette (B). Before sealing it in the 

 side tube the wire is cleaned with a little cold dilute nitric acid, and 

 afterward it is kept in contact with the acid silver nitrate titration 

 solution. In this manner it need not be changed for months. A^ 

 requires occasional cleaning with a little nitric acid and, if neces- 

 sary, fine emery cloth may be used. After titration this electrode is 

 dried with filter paper, taking care not to touch it with the fingers. 

 The tip of the burette may be protected from contact with A' by 

 the glass cap shown on the right of Figure 69. 



Sisco, Cunningham, and Kirk Glass Electrode. An open-cup 

 glass electrode was used by Sisco, Cunningham, and Kirk (1941) 



