394 K. .1. ALLEN AND E. \V. NELSON. 



Using these molecular concentrations, a sea-water of any 

 desired salinity can be prepared. The chlorine content of 

 average Athintic water is about CI = 19'4, and samples of 

 artificial sea- water were prepared with the same chlorine 

 value, thus : 



NaCl . 26-75 



KCl -75 



MgCl, 3-42 



CaCIo -51 



Mgsb, 2-1 



Double distilled water . . , 906-47 



1000-00 



To make this solution comparable to natural sea-water, the 

 "^ alkalinity" must be raised by the addition of an alkali such 

 as Na^CO.s. After the importance of " alkalinity " as a factor 

 had come befoi'e our notice, 2*4 c.c. M/.^ Na^CO.^ was always 

 added to the above solution in order to make the amount of 

 base in equilibrium with CO., equivalent to the usual 40 mgrm. 



Tiie only success we attained with artificial sea-water as a 

 basis for culture media was with four isolated cultures in one 

 of our earlier experiments. Two of these were cultures of 

 C oscinodiscus excentricus in artificial sea-water + 

 Miquel's solutions A and B. The two cultures were identical 

 except that one was in an ordinary bohemian glass flask and 

 the other in a " resistance glass " flask. Xo difference between 

 these two could be seen. The growth obtained in both was in 

 every way equal to normal Miquel sea-water, and is still fair, 

 although over two years old. The other two successful 

 cultures were growths of the same diatom in the same media, 

 plus a small quantity of weed infusion, made by boiling up a 

 small piece of Ulva in artificial sea-water. These gave just 

 as good results, but the addition of unknown factors from the 

 weed detracts from their general interest. In spite of 

 frequent attempts, over fifty in number, we have not been 

 able to repeat this experiment, which may possibly be due to 



