552 R. A. SPAETH 



This series is strikingly similar to the familiar sequence 

 (B) K >Rb >NH4 >Cs >Li >Na 



(Hober '11, p. 408). 



d. Comparative effects of magnesium chloride and sulphate. When 

 scales which have been in a 0.1 M NaCl .solution until the mel- 

 anophores are fully expanded are immersed in a 0.1 M solution 

 of MgCl2, a contraction follows. This contraction as in the 

 case of the potassium salts, varies with the temperature of the 

 solution. The question now arose whether salts of magnesium 

 with a different anion would show the same time of contraction 

 as the MgCL. Upon the basis of the proposed theoretical ex- 

 planation of an independent cation and (secondary) anion ac- 

 tion which seems to exist in the case of the five neutral potassium 

 salts, this might have been expected. Experiments were carried 

 out comparing the effects of 0.1 M solutions of MgCl2 and MgS04. 

 The relatively slight dissociation of MgS04 is well known. At 

 this concentration the MgCU is nearly twice (1.7) as highl}^ dis- 

 sociated as the MgS04. If the contraction effect were a cationic 

 one and dependent upon the number of Mg++ ions in solution 

 the MgCla might be expected to contract the melanophores ap- 

 proximately 1.7 times as rapidly as the MgS04 solution. 



A brief summary of the experiments follows. 



September 1-3, 1912 



Matched pairs of scales were immersed simultaneously by means of 

 the glass dipper in 0.1 M solutions of MgClo and MgS04. All such 

 scales had previously been treated with 0.1 M NaCl until the melano- 

 phores were ■s\adely expanded. In no case were the scales in NaCl 

 longer than an hour. Seven different lots of scales were used from 

 females 7.5 to 8.5 cms. long. In fifty successive trials the melanophores 

 of the scales in MgCl2 did not once contract before those in MgS04. 

 In two cases the contraction times were identical. In the other forty- 

 eight cases the melanophores in MgS04 contracted before those in 

 MgCl2. The time of contracting in MgCl2 was divided b}- the contract- 

 ing time in MgS04 for every pair of scales. This quotient represented 

 the relatively longer time required for the MgCl2 contraction. For 

 example, two scales were immersed in the solutions at 1.00 p.m. MgS04 

 contracted at 1.21; MgCl2 contracted at 1.30. Relatively greater con- 



