jOO Pub. Puget Sound Biol. Sta. Vol. 2, No. 39 



concentration of acids occurred in the long axis of the tank (Fig. 3). The 

 fishes swim back and forth in such a long narrow tank and on encountering 

 differences^ frequently indicate that they sense them by turning back. 

 The sulphuric acid used in the running water experiments was 40 liters 

 of slightly more than a tenth normal solution made up in the Friday 

 Harbor city water. The H2SO3 was a 20-liter bottle made up to about a 

 twentieth normal, but which did not keep for any length of time. Solu- 

 tions of calcium sulphite and calcium hydrogen sulphite were made up 

 and used in the same manner. 



The amount of H2SO3 in the water was determined by titration with 

 N/100 iodine; a quantity of iodine was measured into a flask and a sample 

 of water, usually 25 cc, was introduced under the surface of the iodine 

 and the excess iodine titrated with N/100 sodium thio-sulfate. The flow 

 of H0SO3 in the water when set at any desired point could be maintained 

 for a day at a time at any desired concentration as shown by the iodine 

 titrations. A correction for the iodine absorption by the sea-water 

 was made. This varies from .15 to .125 cc. of N/100 iodine per 100 cc. 

 of water. The calcium hydrgen sulphite was determined by the same 

 method (Sutton, 1911). The HoSO^ was determined by taking account 

 of the amount of the N/100 solution added to the sea- water to make 1 liter, 

 and the hydrogen concentration of the resulting mixture was used as a 

 general guide. This was determined in terms of the pH with buffer 

 solutions and indicators as given by Clark and Lubs (1917); see also 

 Hass (1916) and McClendon (1916). A pH of 7.0 is neutrality; higher 

 numbers indicate alkalinity, lower numbers acidity. These buffer solutions 

 were made up by Dr. Powers and checked against a Hynson, Wescott 

 and Dunning phenol-red colorimeter loaned to us by Prof. C. M. Child. 

 Mixtures of sea-water and N/100 sulphuric acid gave the same pH for 

 the same mixture quite consistently thruout. The variation was only that 

 of the sea-water supply itself which ranged one or two points either side 

 of 8.0. The pH of mixtures of sea-water and sulphurous acid were not 

 consistent, as the pH of a given concentration of acid added to a definite 

 amount of sea-water appears to differ with the length of time the mixture 

 has stood, and the results, except with fresh mixtures, were quite variable 

 and even the fresh mixtures differed considerably from time to time. 

 Whether this is due to the effect of the sulphurous acid on the different 

 indicators or to some other cause has not yet been determined, and only 

 the limits of variation of the mixtures giving a certain pH are shown in 

 any of the work where the pH was used. The oxygen content of the 

 water in which the fishes were killed was taken from time to time by the 

 Winkler method. Carbon dioxide was determined occasionally by titration 

 with sodium carbonate and phenolphthalein indicator, but this method is 



