242 



CHEMICAL CHARACTER OF POTASSIUM 



The table shows that if we wish to replace in normal sea water more 

 Na by Li we must at the same time also replace an increasing proportion 

 of Na by K. 



In order to obtain a more regular curve than expressed in Table III 

 we replaced the natural sea water by a NaCl mixture free from KCl 

 and made up as follows: 



100.0 cc. ofM/2NaCl 

 1.75cc. of m/2 CaCla 

 7.8 cc. of m/2 MgCl2 

 3.8 cc. of m/2 MgS04 

 0.8 cc. of m/10 NaHCOs 



Experiments were then made to ascertain the maximal amount of 

 Li mixture which permitted the formation of swimming blastulas for 

 each given amount of KCl. The results are contained in Table IV. 



TABLE IV, 



Maximal Amount of Li Mixture Permitting Formation of Swimming Blastula. 



When 8 cc. of K mixture were used no more larvae were obtained on 

 account of the fact that this concentration of K itself was too toxic. 



Table IV shows more clearly than Table III that by replacing more 

 Na ions by K ions we increase at the same time the proportion of Na 

 ions which can be replaced by Li ions, without preventing the devel- 

 opment of the sea urchin egg into a swimming larva. 



It was then shown that Rb has a similar but not quite so great an 

 effect as K (Table V). RbCl was also added in the form of a mixture 

 containing all the other constituents of sea water except K and Na. 



