1-17 Salinity Determination by Electrical 

 Conductivity Method. — Salinity detennination 

 of sea water samples by electrical conductivity 

 was demonstrated as early as 1922 by Dr. Frank 

 Wenner, who de\-eloped a shipboard instrument 

 capable of measuring the salinity of sea water 

 to as high a degree of accuracy ( 1 part in 4,000 

 of electrical conductivity) as was possible by 

 means of the more tedious method of titration. 

 Extensive tests and refinements conducted by 

 E. H. Smith and F. M. Soule led to this instru- 

 ment being known as the Wenner, Smith, Soule 

 salinity bridge. The theory involved was that of 

 the instriuuent comparing the electrolytic con- 

 ductivity of a sea water sample with the electro- 

 lytic conductivity of standard sea water. Though 

 the principle has remained basically the same, 

 instruments have been refined, and at the pres- 

 ent time several excellent salinometers (instru- 

 ments for measuring the salinity of a sea water 

 sample) are available to the oceanographer. 



1-18 Equipment Used. — One type of portable 

 induction salinometer now being used by the 

 U.S. Naval Oceanographic Office for salinity 

 determinations of sea water is shown in figure 

 I-IO. The salinometer weighs 48 pounds and is 

 housed in a fiberglass carrying case. The instru- 

 ment is simple to operate and maintain. Results 

 obtained have proved to be accurate, precise, 

 and reproducible within satisfactory limits. 

 A block diagram of the instrument is shown 

 in figure I-ll. A sample of sea water is drawn 

 into the cell for the analysis. This liquid acts 

 as a single turn loop to provide a link coupling 

 between the transmitter toroid and the receiver 

 toroid for a 10 kc. oscillator signal. The degree 

 of coupling is directly porporticnal to the con- 

 ductance of the sea water loop. The coupling be- 

 tween the two toroids is alternated by operator- 

 controlled transformers until two currents of 

 equal magnitude (It and Ir), but of opposite 

 phase, are indicated on a nullmeter. The con- 

 trol settings then are translated to salinity 

 values with tables. 



Another model induction salinometer that 

 will be in use at the U.S. Naval Oceanographic 

 Office in the near future is described in para- 

 graph 1-25. 



1-19 Setting Up the Salinometer. — The sal- 

 inometer should be set up on a work table with 

 adequate room for sample bottles, log sheet, and 

 drain bottle, and the following preliminary ad- 

 justments should be made to the instrument 

 (fig. 1-12) : 



Step 1. Attach a 10- or 12-inch piece of ''/iq- 

 inch outside and %6-inch inside diameter natu- 

 ral latex tubing (A) to the sample cell. 



Step 2. Attach a 4- foot piece of the latex tub- 

 ing (B) to the drain tube of the sample cell. 

 Run the tube into a large waste bottle. 



Step 3. For model RS-7A, attach an air re- 

 lief tube (C), a 4-inch piece of latex tubing, to 

 the air relief inlet (D) of the sample cell, and 

 place a screw clamp (E) across the tube. For 

 some models that are equipped with the fill 

 knob (F), which performs the same function 

 as the screw clamp and the air relief tube, this 

 step is not necessary. 



1-20 Preliminary Checkout. — Before the 



analysis is commenced, the instrument should 

 be checked as follows: 



Step 1. Check to be sure that the null indica- 

 tor (G) needle reads zero (with power off). 

 If needle is off zero, breathe on meter to elimi- 

 nate any static charge. If needle is still off zero, 

 correct by adjusting small screw below needle. 



Step 2. Connect power cable (H) to 110 v. a.c. 

 outlet, turn on power switch (I), and allow 1 

 minute warm up. Set Conductivity Ratio dials 

 (J) to zero, set Function Selector dial (K) to 

 Salinity, and set Standardization dials (L) to 

 zero. Again check null Indicator. If it does not 

 read zero, remove panel screws, slide chassis out 

 of the case, and adjust Zero Adjustment with 

 screwdriver (fig. 1-13). 



Step 3. Set Standardization dials to 5000. 

 Change Conductivity Ratio dials by 0.00001, 

 0.00002, etc., to observe meter sensitivity. Meter 

 deflections should be perceptible for the small- 

 est change and should be reasonably linear for 

 the first few steps. 



Stej) 4. Set the Function Selector to Tem- 

 perature and adjust Temperature °C. controls 

 (M) until null indicator meter reads zero. This 

 temperature should be approximately room 

 temperature. 



Step 5. Set the Stir Fill switch (N) to Fill, 

 and listen for sound of the pump to make sure 

 the pump motor is functioning. 



Step 6. Screw the overflow jar (O) into 

 place, and turn the three-way valve (P) to Fill 

 position. Place fill tube in a bottle of water, ad- 

 just air relief tube clamp (or fill knob) to ob- 

 serve that pump is drawing water into sample 

 cell. 



1-21 Filling, Rinsing, and Draining the 

 Sample Cell. — Proper filling of the sample cell 

 is probably the most miportant technique in the 

 operation of the salinometer. Proper rinsing 

 between samples ranks next in importance. The 

 water must be drawn into the sample cell in 

 such a way that bubbles do not form on the in- 

 ner surface of the cell. The sample cell should 

 be rinsed carefully with a cell full of the new 

 sample each time a different sample is to be 

 analyzed. When the sample cell is drained care 

 must be taken to avoid contaminating the sam- 

 ple. The steps listed below should be performed 



I-ll 



223-812 O - 68 ■ 



