CHAPTER XI. 

 ELECTROLYTES. 



It has already been intimated that much of the conduct of osmotic 

 membranes, which might otherwise appear mysterious and capricious, 

 becomes explicable, if one regards the membranes as having a purely 

 colloidal structure. This provisional view of their character has been of 

 great utility as a working hypothesis throughout the present inves- 

 tigation, inasmuch as it was only by proceeding in accordance with 

 its suggestions that we have been able to obtain, and to maintain in 

 efficient condition, membranes which were truly semi-permeable and 

 therefore adequate for the measurement of osmotic pressure. Much that 

 is to be said in this connection has been stated, and in some instances 

 strongly emphasized, in previous chapters, particularly in Chapter IV. 

 But the question of the structure of the membrane is of such funda- 

 mental importance to the measurement of osmotic pressure that the 

 author makes no apology for recalling here those peculiarities of its 

 behavior which suggest that its structure is colloidal. They are : 



1. The destructive effect of an accumulation of alkaline hydroxides in 

 the cell during the deposition of the membrane by electrolysis. — This is not, 

 in itself, convincing evidence of the colloidal nature of the membrane, 

 but it acquires some weight in that direction when it is observed that 

 the deterioration of the membrane, under the circumstances, can not 

 be fully accounted for by the solvent action of the alkali upon it, but 

 is probably due, in a great measure, to an accumulation of the cations 

 in the membrane material. As bearing upon this phase of the subject, 

 we will mention the beneficial results which are obtained (1) by greatly 

 diluting the solution of potassium f errocyanide ; (2) by substituting for 

 the potassium salt, lithium ferrocyanide whose cation is much less harm- 

 ful to colloidal structure; and (3) by employing ferrocyanic acid, rather 

 than any of its salts. 



2. The impossibility of forcing the resistance of any membrane above a 

 given value by continued electrolysis. — That progress is stopped in this 

 case by an accumulation of potassium in the membrane is made 

 extremely probable by the fact that, after soaking the membrane in 

 water free from electrolytes and then resuming the electrolysis, a much 

 higher resistance is obtained. 



3. The decline in resistance, and the ultimate ruin of the membrane, 

 which result from a too long continued electrolysis. — This also points to 

 an accumulation of potassium in the membrane, which diminishes and 

 finally destroys its semipermeable character. 



4-. The remedial effect of soaking in pure water membranes which, from 

 any cause whatsoever, have partially lost their semi-permeable character. — 

 The improvement of the membranes under such treatment has not yet 



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