2 NAVAL RESEARCH LABORATORY 



on the basis of clarity and freedom from foreign material. Data concerning these samples 

 will be found in Table 2. The samples were received within one to four days after collection, 

 and their sound velocity was determined with a one-megacycle ultrasonic interferometer 

 as soon as received, and at intervals throughout the investigation. Chlorinities were 

 determined by the Mohr method of AgNOs titration using a special elongated-scale burette 

 made by the Machlett Company and patterned after a modification of the original Mohr 

 burette suggested by the Woods Hole Oceanographic Institution. Toward the end of this 

 investigation a potentiometric titration with the Beckman automatic titrator and a Ag-AgCl 

 electrode in conjunction with a calomel reference electrode was developed. This technique 

 frees the operator from the close control required as the end point is approached, and 

 eliminates the human factor in choosing the relatively difficult to determine colorimetric 

 end point. 



The temperature of the interferometer bath was controlled by Magna-Set thermo- 

 regulators adjusted to better than i0.01° C by means of a Leeds and Northrup 8160 Platinum 

 Resistance Thermometer in conjunction with anL&N G-1 Mueller Bridge and an L&N 

 2430-A galvanometer. The interferometer cell temperature was determined by Bureau of 

 Standards calibrated mercury-in-glass thermometers which could be estimated tot0.02° C. 



To obtain various salinities in the range 19-41 parts per thousand, the natural sea 

 water samples were diluted with distilled water and evaporated under vacuum. The 

 chlorinity of each of the solutions was actually determined by Mohr titration in the same 

 manner as the chlorinities of the original samples. The salinities were calculated by the 

 empirical relationship established by an International Commission (8) . This relationship is 



Salinity = 0.03 + 1.805 x Chlorinity. 



Sound velocities in the various sea water samples obtained by the above method were 

 determined over a temperature range of 0° to 40° C. The measurements were made at a 

 one-megacycle frequency, but several determinations were made at three megacycles. • 



RESULTS AND DISCUSSION 



The experimental determinations of sea water soimd velocity were plotted in two 

 series of graphs (not given here), velocity vs. temperature with salinity parameter and 

 velocity vs. salinity with temperature parameter. The points in the latter graph formed 

 straight lines for individual temperatures. From this graph, velocity values at integral 

 temperatures and salinities were read to io.l meter per second. These values were then 

 processed by the method of least squares to yield the following empirical equation for the 

 velocity of sound in sea water over a range of salinities from 19-41 parts per thousand 

 and a range of temperatures from 0° to 40° C. 



1448,6 + 4.618 tc - .0523 tc T"- d Q- 3^ 



'm 



+ 1.25 (S-35) - .011 (S-35) (tc) + .0027 x 10'^ (S-35) tg 

 -2 X lO"'' (S-35)* (1 + .577 tg - .0072 tc^) 



The last term of this equation becomes significant as salinity approaches zero, and yields 

 velocities in agreement with experimental values for distilled water (S = 0°/oo). However, 

 as no determinations were made from 0-19 parts per thousand salinity, the use of this 

 equation in this range of salinities is not recommended. In Table 3 the experimental 

 determinations of velocity are compared with the velocities corresponding to the same 

 physical conditions obtained by the use of the empirical equation. 



