28 Papers from the Department of Marine Biology. 



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 (iMcClendon, 1916). 



The work was brought to the present state of completeness in Min- 

 neapolis, and the expermients 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 expermients. 

 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 necessary in order to make possible the 

 duplication of the experiments by the indicator method. There was 

 not sufficient time for another series of expermients 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 Ph 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 

 Ph are affected by absorption of CO2 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 mm. nonsol tubes containing the indicator. These tubes should 



