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Results Applied to Oceanography and Measurement of Respiration-Rate of Marine Organisms

indicator, experiments, buffer, method and temperature

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All of the P. determinations were made with the hydrogen electrode, but at the same time the indicator method was calibrated so that the results may be duplicated by this more convenient method. The indicators used were mostly selected from the list shown in figure 3. It was found that the sulfophthalein series gave the most reliable results because of the brilliancy of the colors and the fact that they are differently colored in acid solutions and hence the change is qualitative and not quantitative. An error due to a difference in concentration of the indicator may be at once observed, whereas this is not possible with phenolphthalein. Dibrom-o-cresolsulfophthalein has the same range as p-nitrophenol; dibromthymolsulfophthalein has the same range as phenolsulfophthalein ; dibromthymolsulfophthalein has about the same range as a-naptholsulfophthalein.

Part of the work was done at Tortugas, Florida, and the sea-water was drawn directly from the sea into the apparatus, but owing to the inability to work at any temperature except 30° and also to the incom pleteness of the library, the work could not be finished there, at least in one summer. Part of the results obtained at Tortugas have already been published (McClendon, 1916).

The work was brought to the present state of completeness in Min neapolis, and the experiments at 30° are in close agreement with those made at Tortugas. The sea-water that had been used in aquaria, even those of pyrex glass, was deficient in non-volatile buffer, due to the action of organisms, and could not be used in standard experiments. In all of the Minneapolis experiments one of the sulfophthalein indi cators was added to the extent of 1 mg. to 100 c.c. of sea-water, and so increased the non-volatile buffer to this slight extent; this causes a small theoretical error, but was necesary in order to make possible the duplication of the experiments by the indicator method. There was not sufficient time for another series of experiments without the indi cator, as the sea is too complex a solution to be treated in any simple mathematical manner, and it was necessary to make a large number of direct determinations over a wide range of conditions. Some of the

determinations were repeated from 2 to 10 times before we were confident of the correctness of the results. During the investigation the solution of o-cresolsulfophthalein was accidentally lost and a new one was prepared in the same manner and from a bottle of the same label by the same manufacturer. It was found that a buffer mixture containing this indicator had the same color as a buffer mixture of 0.15 higher P. colored with the old solution. This led to a repetition of much of the work. It has long been known that such an experience may be had with any indicator, but it is hoped that these excellent indicators may be manufactured in larger quantities, so as to insure greater uniformity, and that each yield be numbered and so labeled.

Alkaline solutions of borax and other buffer mixtures of standard P. are affected by absorption of by the air and solution of glass. Those sealed in 1 cm. nonsol glass tubes were found to keep for about a year. In order to increase their life and accuracy, new solutions of higher buffer value were standardized and sealed (by fusing the glass) in 24 min. nonsol tubes containing the indicator. These tubes should be good for 5 years, provided they are kept in the dark most of the time.' Details of the indicator method and the colorimeter that we used are given on pages 44-46, and we will now pass on to the question of the duplication of our results by the indicator method.

We found the P. of sea-water to be practically independent of salinity or temperature between 20° and 30°, and all of our experiments at 10° indicate that even this drop in temperature does not appreciably affect the P.. Our values given for 0° are extrapolated from data on the assumption that the P. is independent of the temperature.

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