1885.] Metals during Diffusion of Salt and Fresh Water. 375 



compare favourably with statistics (examined and formerly referred 

 to by the author, and some of which are given in the Appendix) as 

 to differences of composition between surface and bottom waters 

 during diffusion in some portions of such a tidal stream as the 

 Thames, and therefore afford an approximation to effects arising from 

 similar conditions existing during such tidal action ; the propor- 

 tional difference of salinity between top and bottom waters in parts 

 of the Thames during certain states of tide, &c, being, however, 

 sometimes greater than the experimental divergencies given on 

 Table B. 



Table B. — Analysis of Water from Diffusion Cell. Results in grains 



per Gallon. 



Time from 

 commencement 

 of each diffusion. 



Sodium chloride 

 from position 

 (a) near bottom. 



- 



Sodium chloride 

 from position 

 (b) near surface. 



Difference of 

 composition 

 between water 

 about (a) and (b) 



1 day.. 



1-44 



1-32 



0-12 





2-87 



2-64 



0-23 



3 „ 



4-31 



3-95 



0-36 



4 „ 



5-90 



5-01 



89 



5 „ 



7-64 



5-81 



1-83 



6 „ 



9-38 



6-61 



2-77 



7 „ ....... 



11 12 



7-41 



3-71 



8 „ 



22-19 



19-42 



2-77 



9 „ 



33 26 



3143 



1-83 



10 „ 



44-32 



43 -44 



■0-88 



11 „ 



50-14 



49-79 



0-35 



12 „ 



50 -73 



50-49 



24 



13 „ 



51-32 



51 -19 



13 



14 „ 



51 -90 



51-90 



Nil. 



The samples of water for analysis were carefully taken from vessel F by pipette 

 at points indicated on fig. 1 for convenience and accuracy, so as least sensibly to 

 disturb the solution. 



The electric action between the plate (which was the positive 

 metal throughout the whole period) in the sea water and that in the 

 other water, was in course of the research ascertained by occasionally 

 introducing in the circuit a delicate galvanometer of known resist- 

 ance and constants, and the resistance of the cells having been 

 regularly determined, the highest E.M.F., in the case of two repre- 

 sentative plates, was found to be about 0*14 volt, which gradually 

 reduced as diffusion proceeded. 



The loss by simple corrosion in the sea water alone, as compared 

 with that taking place in the diffusing salt and fresh water, is shown 

 by the relative behaviour of the two plates A and C, of the same 



