36 
Proceedings of the Royal Society of Edinburgh. [Sess. 
colour, allowed those granules less rich in chlorine to pass through it. He 
suggests that the original colloidal solution contains a mixture of granules 
formed of from 1 to 4 molecules of Fe 2 (OH) 6 grouped round the H ion 
of a HC1 molecule, the smaller granules being able to pass through the 
membrane. Goodwin * examined the hydrolysis of ferric chloride, making 
measurements of electrical conductivity and of freezing-point lowerings. 
He came to the conclusion that the colloidal reaction taking place in 
hydrolysis serves to put the FeOH" ions out of the solution. Jones, 
Getman, etc.,j* have made measurements of electrical conductivity and of 
freezing-point lowerings in the case of ferric chloride and nitrate, and have 
calculated the number of molecules of water in combination with each 
molecule of salt in the case of the nitrate. The conclusion drawn by 
Malfitano and Michel J from their observations on the hydrolysis of ferric 
chloride is that the products of hydrolysis are not constant in composition, 
and that the difficulty with which these products are re-converted into 
ferric chloride by the hydrochloric acid present, increases as the hydrolysis 
proceeds. The hypothesis is put forward that the colloid is composed of 
complex ions. 
The result of all the work carried out on this subject points to the fact 
that, when ferric chloride is dissolved in water, the following reversible 
action takes place : — 
Fe 2 Cl 6 + 6H 2 0^±Fe 2 (0H) fi + 6HC1. 
The amount of hydroxide formed depends, amongst other things, on the 
concentration of the solution and on the temperature. Besides this, a 
secondary reaction seems to take place according to the formula 
Fe 2 Cl 6 + Fe 2 (0H) 6 ^±2Fe 2 0 3 + 6HC1. 
If the hydrochloric acid is neutralised by the addition of ammonia, a floccu- 
lent brown precipitate of Fe 2 0 3 is formed. The constitution of the colloidal 
hydroxide is very probably Fe 2 Cl 6 a?Fe 2 0 6 H 6 , where x is a large number, 
as shown by Magnier de la Source § and Sabanejew.il 
In the present investigation the salts examined were ferric chloride, 
bromide, nitrate, and sulphate, and ferrous chloride and sulphate ; they 
were all obtained from Kahlbaum. Ferric chloride consisted of dry yellow 
* Goodwin, “Ueber die Hydrolyse des Eisenchlorids, 55 Z. phys. Ghem ., xxi. p. 1, 1896. 
t Jones, Getman, etc., “Hydrates in Aqueous Solution, 55 Carnegie Institution of 
"Washington, Publication Ho. 60, 1907. 
$ Malfitano and Michel, Compt. rend., cxlv. p. 185 and p. 1275, 1907. 
§ Magnier de la Source, Compt. rend., xc. p. 1352, 1880. 
|| Sabanejew, Ghem,. Gentralbl. , i. p. 11, 1891. 
