68 



TO OPERATE APPARATUS 



Turn the bottom snaj) switch to '"on" position, thus starting stir- 

 ring motor. 



Tmn middle snap switcli to ''on" position thereby putting current 

 on tjio relay, thermoregidator. and first heater. This automatically 

 brings tiie bath temjiorature to 25.15° C. and maintains it at that 

 temjieratm^e. 



The top snap sMitcli controls t]ie current to the second heater or 

 suj)er]ieater. This Jieater has no thcrmoregulator and is only used 

 when it is desired to bring the bath quickly to the regidating temper- 

 ature. This to]) switch is normally ke})t in '"off" ];osition. "\AlTen- 

 ever it is turned ''on" the ()j)erator should .stand by the ai)j)aratus 

 and when mercury shows in the bath thermometer, switch it "of!" 

 autl let the first heater bi'ing the temperature uj) to the testing point. 

 Undei" no circumstance shoidd the tem])erature of the bath be per- 

 mitted to 2-ise beyond 27° (\ as such a high temjierature causes the 

 merciuy in the thciiuoi'cgulator to exjjand out through the to]) of 

 tlie glass tube and change the critical temjierature at which the 

 thcrmoregulator automatically opei'ates. 



Tlu're is a salinity tabic pre])ared for this a])])aj'atus giving the 

 salinity that corresj^onds to each reading of tlic slide wire. The 

 "Y" cell contains water whose salinity is ap[)roximately kno"wii 

 (about 500 on the slide wire). Place water of know^l salinity in the 

 "X" cell (near 500 on the slide wire) and when the bath comes to 

 the desired temperature (25.15° C), note reading on slide wire. If 

 this i-eading does not fall on the salinity curve for water of tPiis kno^^^l 

 salinity, then adjust the j-esistance on the "Q" dials luitil tjie salinity 

 of water in the "X" cell as shown by slide wire is the same as the 

 known salinity. This is done by setting the slide wire at the reading 

 corresponding to the known salinity of the water in the ''X" cell. 

 Then balance the bridge })y varying the resistance on the "Q" dials 

 until the sound of humnuM- is a mininuun. This setting of the "Q" 

 dials sluuild not be changed as long as the M'ater in the "Y" cell 

 undergoes no change in salinity. The '-y'' cell sliould be sealed 

 with jjaiadine to ]>revent evapoi'ation. 



The actual woj'k of balancing })ridge is as folloAss: 



1. Adjust the setting of the slide wiie so as to biing the sound in 

 tlie telej)lione receivers to the mijiinunn intensity. 



2. Without changing the setting of the slide wiie adjust the mutual 

 inductance so as to furlhci- ic'Hucc tli(> soiijid in the telephone receiv- 

 es, if possible. 



3. \Vitliout changing cither the slide wiie or nuitual inductance 

 and with the ground switch closed (sn\all single ])ole-knife switch), 

 adjust thci slider on the third biancli of the bridge (resistance coil 



