ARTIFICIAL SEA WATERS: 



Sea waters all over the world contain the same proportions of the 

 various ions, differing only in the total ionic content and therefore 

 in total osmotic pressure. The osmotic pressure is proportional to the 

 salinity of the sea water, this being defined as the total grams of solid 

 per kilogram of sea water when all the halides have been converted to 

 chloride, all the carbonate converted to oxide, and all the organic matter 

 completely oxidized. The salinity of Woods Hole sea water is 31 0/00±0.5. 

 All the formulae given below have been recalculated to the same salinity, 

 and therefore the same osmotic pressure, as Woods Hole sea water. 



A true artificial Woods Hole sea-water, called M.B.L. formula, is 

 listed in the table below. This contains all the major ions in amounts 

 identical with Woods Hole sea water as it comes from the sea water taps, 

 except that the fluorides, bromides and iodides have been replaced by 

 chloride, the strontium replaced by calcium, and the borate omitted. In 

 the Trace M.B.L. Formula, however, these minor elements are included in 

 their proper amounts. These formulae have been tested on sea urchin eggs 

 by Ethel Browne Harvey and have been found to be both osmotically and 

 physiologically satisfactory. They are the recommended formulae for use 

 at the M.B.L. 



The other listed formulas are experimental sea waters which were 

 used by the investigators whose names are applied to the solutions. They 

 all differ from sea water in all components, but contain approximately 

 the same amounts of the various ions as sea water (compare with M.B.L. 

 formula). The Allen (Pantin) and Brujewicz formulae correspond most 

 closely to true sea water, all the others being low in sulfate and 

 equivalently higher in chloride. The Van't Hoff formulae are low in 

 calcium and lack the buffer action of bicarbonate, whereas, the Challenger 

 sea water contains over double the normal amount of calcium. The two 

 calcium-free formulae both replace the calcium with sodium so as to main- 

 tain osmotic pressure, but the Shapiro formula is also low in magnesium. 



The listed quantities of the various salts are mixed in a 1 liter 

 volumetric flask and diluted to the mark with distilled water. It is 

 best to weigh out the sodium chloride, but to burette the LOOM solutions 

 for all the other components. Ml. of LOOM refers to milliliters of LOOM 

 solution of the salt. Be sure to check the notes below the main table for 

 any minor constituents which must be added before diluting to volume. 



54- 



