MOVEMENTS OF HERRING AND OTHER MARINE FISHES. 319 



Hydrogen sulfide is very commonly present in sea water when 

 decomposition is taking place. This was determined by titration 

 with iodine which was the only method we were equipped to 

 employ. It is never present in any quantity in freely circulating 

 waters. The highest records are for collections made near the 

 bottom under Ulva, where the odor is often quite distinct. On 

 account of the probable presence of other substances which may 

 absorb iodine the determinations may be slightly too large 

 (Birge and Juday, 'ii). 



Table I. 



The Dissolved Gases of the Sea Water about Friday Harbor, 

 Washington. Data in c.c. per liter. 



It will be noted from a study of the table that the water from 

 Point Caution where the tide has full sweep is the only water 

 saturated with oxygen at the surface. In other places the sea 

 water at the surface is about i c.c. less than the amount given 

 by Fox (see Murray and Hjort, '12, p. 254). Aerating the sea 

 water increased the oxygen. The water from the tank did not 

 seem to have been modified by standing for sixteen hours or more. 

 On the whole there must be much decomposition in Puget Sound 

 waters. There was no constant difference between the water 

 from outside and inside the side of the island which encloses 

 Friday Harbor. The CO2 is a little higher except at low tide 

 in the sample taken near the Ulva; the oxygen remains about the 

 same. The hydrogen sulfide does not average appreciably higher. 



The explanation for the alkaline character of the water under 

 the Ulva is that the plants take up the CO2 and give off oxygen 

 and thus remove the excess which occurs in other localities. 



