186 



croelectrodes for the oxygen determination. Muller (1947) describes the use of 

 a platinum microelectrode in a cell in which the test solution is made to flow 

 past the electrode at a controlled rate. 



Platinunn microelectrodes (or other stable metallic electrodes) are the 

 only electrodes that appear to be applicable to polarographic analyses on ship- 

 board. In the usual polarographic techniques, a D. C. potential is applied to the 

 electrode to achieve concentration polarization. In solutions containing several 

 reducible substances, all may be reduced at the cathode. In the case of sea wa- 

 ter, although the principal reducible substances is dissolved oxygen, many of the 

 trace metals will also be reduced but being in extremely low concentrations their 

 reduction will not contribute measurably to the diffusion current of oxygen. Nev- 

 ertheless, the surface of a micrometallic electrode will gradually accumulate a 

 surface film of these trace metals. The "plated" electrode then will have differ- 

 ent properties than the initially clean surface and the calibration of the electrode 

 will be changed. 



Olson, Brackett, and Crickard (1949) obtained much improved stability 

 by applying in place of the D. C. polarizing potential, a square wave potential 

 composed of a positive pulse, a shorting period, a negative pulse, and a short- 

 ing period, to a stationary platinum electrode. 



Carritt (unpublished results) combined the Olson et al. (1949) and Muller 

 (1947) techniques in such a way that a seagoing polarographic instrument for the 

 oxygendetermination appears possible. A polarographic instrument with a solid 

 microelectrode can, at least in principle, be adapted to continuous in situ meas- 

 urements of oxygen concentration. In addition, the dependence of the diffusion 

 current on the velocity of flow past the electrode, shown in the Muller technique, 

 suggests that such a device might be adapted to measuring the velocity of water 

 moving by the electrode. 



The specificity of a polarographic wave, together with the sensitivity of 

 the method in dilute solutions, offers many advantages for the analysis of con- 

 centrates obtained from extraction columns, etc. 



SPECIAL SHIPBOARD DEVICES 



Many shipboard chemical procedures can be improved by employing 

 "gadget- type" instruments to perform operations which, on shore, in the ab- 

 sence of a "moving laboratory", present no problem. Useful gadgets of home 

 design and construction can be found in most laboratories, but unfortunately 

 many of them are not described in the literature. An Automatic Reagent Dis- 

 penser for Shipboard Use was recently described by Wooster et al. (1951). The 

 instrument permits the rapid addition of precisely measured quantities of a rea- 

 gent to serial analyses. This is the kind of operation that becomes tedious and 

 time-consuming when done at sea with conventional apparatus. 



DISCUSSION: Clifford A. Barnes 



I can add little to Dr. Carritt's very able summary of the present trend 

 towards instrumental and in situ measurements of chemical properties of sea 

 water. There are a few observations, however, that might serve to emphasize 

 some of his points. 



The need for tailoring the instrument or method to fit the particular 

 problem at hand is often overlooked. The quick responding STD and CTI and 

 the CTD of the U.S. Navy Electronics Laboratory are well suited for defining 



