240 CHEMICAL CHARACTER OF POTASSIUM 



The NH4 ion, therefore, resembles in its physiological behavior the 

 K ion more than it does the Na or Li ion. 



///. The Antagonism between Li and K. 



In any series of ions based on their chemical or physical behavior Na 

 occupies a position between Li and K. Li has a smaller and K has a 

 larger ionic radius than Na. If we replace some of the Na ions of sea 

 water by Li ions we alter the properties of the solution in one sense, 

 and if we replace part of the Na ions by K ions we alter the properties 

 in the opposite sense. We should, therefore, expect that if we re- 

 place a certain percentage of Na ions in sea water by Li ions the toxic 

 character of the solution should be diminished if we replace at the 

 same time also a certain percentage of the Na ions by»K ions; since 

 with the combined increase of the K ions and of Li ions the effect of Na 

 ions might be more nearly approximated. 



The newly fertilized egg of the sea urchin (Arbacia) can develop into 

 gastrulae in an "artificial sea water" of the following composition. 



100.0 cc. ofM/2NaCl 

 1.75CC. of M/2CaCl2 

 2.2 cc. ofM/2KCl 

 7.8 cc.ofM/2MgCl2 

 3.8 cc.ofM/2MgS04 



To this was added 0.8 cc. of m/10 NaHCOs to bring the artificial sea 

 water to a pH of about 7.4. 



We prepared the following solution in which m/2 NaCl of the arti- 

 ficial sea water was replaced by m/2 LiCl and which was free from K. 

 Its composition was: 



100.0 cc. of m/2 LiCl 

 l.TSccof M/2CaCl2 

 7.8 cc.of m/2 MgCl2 

 3.8 cc. of m/2 MgS04 

 0.8 cc. of M/lONaHCOa 



This solution, which we will call the Li mixture, permitted us to 

 replace the Na in natural or artificial sea water by Li without alter- 

 ing the constitution of the sea water in any other direction except in 

 regard to K, the concentration of which it was our intention to vary 

 in the experiments. 



