Absorption Spectra of Dilate Solutions. 143 



with the law of Guldberg and Waage. This is, however, here not the 

 case. The equilibrium which takes place in dilute solutions of ferric 

 chloride may be most simply represented by the equation 



FeCl 3 + 3H 2 ZT Fe(OH) 3 + 3HCl. 



Suppose that to begin with one gram molecule of FeCl 3 was dis- 

 solved in n molecules of water, neither hydrochloric acid nor ferric 

 hydroxide being present. When the equilibrium is reached, sup- 

 pose that a fraction x of the ferric chloride molecules have been 

 decomposed. Then we have (1 x) molecules FeCl 3 , x molecules 

 Fe(OH) 3 , 3x molecules HC1, and (n 3x) molecules of water. As n 

 is large compared with 3x, this may be taken as the same as n. 



According to Guldberg and Waage these quantities should be con- 

 nected together by the equation 



fr-')" = 3K . . (3), 



x is identical with the loss of iron given in Table XI divided by 

 100, and, calling the concentration of the original unfiltered solution 

 (with regard to Fe) = c, we have 1 gram molecule FeCl 3 in 1/c litres,. 

 or, as 1 litre of water contains 55*5 gram molecules, we have 1 gram 

 molecule FeCl 3 in 55'5/c = n gram molecules H 2 O. Putting these 

 values in the above equation we get 



_0^) = JL K = i/ 



x* . c ' 55-5 



The values of 1c lt calculated from the different values of x, are 

 given in Table XI, and are evidently very far from being constant, 

 as is required by the law of Guldberg and Waage. 



The agreement is hardly improved by regarding the ferric hydroxide 

 as an insoluble body and putting its active mass constant. The 

 equation then becomes 



- -- - = const. = & 2 . 

 xc 



The values ef Jc 2 also vary considerably, as Table XI shows. 



According to the equation for the equilibrium of four electrolytes 

 given by Arrhenius,* however, K, on the right-hand side of equation 

 (3), is not a constant. For Arrhenius regards only those parts of the 

 electrolytes which are dissociated into their ions as the active masses, 

 so that if a l5 2 , a 3 , and 4 are the fractions of the electrolytes FeCl 3 , 

 H 2 O, Fe(OH) 3 , and HC1 respectively, which are dissociated, we must 

 substitute for the equation of Guldberg and Waage the expression 

 * ' Bihang k. Svensk. Yet.-Ak. Hand./ vol. 8, No. 14, 1884. 



