72 Papers from the Marine Biological Laboratory at Tortugas. 



DETERMINATION OF CHLORINE. 



Chlorine was estimated by means of the salinity outfit supplied by the 

 Copenhagen laboratory of the Conseil permanent international de la mer. 

 This apparatus was obtained through the courtesy of the United States 

 Bureau of Fisheries. The procedure is an adaptation of the usual method 

 of estimating chlorine by titrating with silver nitrate in presence of potas- 

 sium chromate. An essential feature is a sealed tube of standard sea- 

 water whose content of chlorine has been very carefully determined. This 

 water is used for comparison and the apparatus is so constructed and cali- 

 brated as to insure maximum accuracy. Standardized burette No. 8, 

 measuring about 1.5 mm. between graduations, and pipette No. 3, having 

 a capacity of 15.04 c.c, were used. Standard sea-water P7 2/2, 1912, with 

 a chlorine content of 19.386 grams per kilogram, was titrated frequently 

 during the tests at Tortugas. In the later tests comparison was made 

 indirectly with the same standard by means of a large sample of sea-water 

 from Tortugas that had been titrated se^ eral times. Knudsen's correction 

 {k) has been applied to the titrations^ and salinity {S) has been computed 

 by means of his formula,^ in which CI represents grams per kilogram of 

 chlorine: S = 0.030 -f 1.805 CI. 



SPECIFIC GRAVITY. 



Density was determined by comparison in 10 c.c. weighing flasks with 

 distilled water at 25° C. Knudsen's values^ for pn.5 were used for com- 

 puting density iSyfr^) as follows Sr^ = i + prim, where pn.s = i. 00129 

 (0.1245 + o-o — 0.05950-0 + 0.0001550-0^) and co = — 0.069 -f 1.4708 

 CI — 0.001570CF + 0.0000398 CF. Part of the relatively slight difference 

 between determined and computed figures for sea-water around Biscayne 

 Bay may be attributed to difference of standard; that is, by the deter- 

 mined value the sea- water is compared with distilled water at 25° C.^ 

 while by the calculated value the specific gravity of the sea-water at 

 17.5° is referred to distilled water of the same temperature. 



SEA-WATERS AT TORTUGAS. 



It is believed that solution of calcium carbonate by carbon dioxide in 

 sea-water, if such action takes place, would be shown by regular differences 

 in condition of carbon dioxide in the ebb and flood waters passing out of 

 and into the lagoon surrounded by the shoals and keys of the Tortugas. 

 Accordingly, samples of sea-water were collected twice a day from the 

 middle of Southwest Channel about a mile southeast of Loggerhead Key; 

 these were taken in bottles provided with washered caps that could be 

 clamped down to prevent escape of gases and the samples were kept on 

 ice until they were examined. Those collected from June 11 to 16, inclu- 

 sive, were tested immediately, and though those taken before the former 

 date had been stored for several days the tests do not indicate that the 

 delay in examination had any appreciable effect on their composition. 



> Knudsen, Martin, Hydrographical tables. Copenhagen, 1901. 



