164 DE. B. D. STEELE, DR. D. McINTOSH AND DR. E. H. ARCHIBALD 



Thus WALDEN and CENTNERSZWER ( 'Zeit. Phys. Chem.,' 1902, 39, p. 513) found 

 that the molecular weight of potassium iodide dissolved in hydrocyanic acid is twice 

 as large as the normal. ABEGG ('Die Theorie der electrolytischen Dissociation,' 

 p. 103) has pointed out that this can be explained by the assumption that the 

 undissociated substance is polymerised ; in which case a high average molecular 

 weight might occur even with considerable ionisation. 



A compound such as (KI) 4 , for example, if it were completely dissociated into two 

 ions, would have an average molecular weight of 332. We find that in most cases the 

 molecular weight increases with increasing concentration, and although the opposite 

 change occurs in dilute aqueous solution, this variation is the same as that which 

 takes place in more concentrated aqueous solutions. 



This will be seen from the following comparison of the figures for acetone dissolved 

 in hydrogen bromide with those for lithium bromide dissolved in water, the latter 

 figures being taken from a recent paper by JOXES and GETMAN ('Zeit. Phys. Chem.,' 

 1904, 49, p. 390). 



(a) Acetone in hydrogen bromide 



c = concentration in gram-molecules per litre = 0'51, 1'17, 1'85, 2'5G ; 



- = molecular depression = 4 '5, 4 '5, G'5, 11 '5. 



C- 



(&) Lithium bromide in water 



c = 0'48, 0-97, 1-94, 3'88 ; A = 4'07, 4'41, 5'31, 7'86. 



JONES and GETMAN attribute the apparent increase in the number of molecules in 

 more concentrated solution to the formation of hydrates in solution. 



The low molecular weight which we have found for triethylammoniam chloride in 

 sulphuretted hydrogen, although at first sight difficult to reconcile with the hypothesis 

 of association, is not inconsistent with it. 



Thus if the compound formation and subsequent dissociation takes place according 

 to the general scheme 



nAB+mCD ^ (AB),, (CD) W 

 and mj .0 



(AB), (CD) m (AB),, (CD) m +mD, 



and if dissociation were nearly complete, it is evident that if m is equal to or greater 

 than n, a larger number of molecules than n would be formed, and therefore the 

 average would be less than the theoretical molecular weight. 



We can offer no suggestion as to why toluene, when dissolved in hydrogen chloride, 

 although it absolutely fails to conduct the current, possesses such an extremely low 

 molecular weight. Similar cases have been observed by KAHLENBERG, but no 

 explanation has been suggested. 



