of Edinburgh, Session 1880 - 81 . 
193 
use in hydrochloric acid solution, which is as dilute as the sulphuric 
acid solution is when it is commonly titrated. But the chief want 
of the analyst is the power to titrate strongly acid hydrochloric 
solutions of iron with permanganate, and I find that this can he 
done without difficulty. As long as there is ferrous salt in the 
solution the permanganate devotes itself exclusively to it ; hut as 
soon as it is all transformed into ferric salt the permanganate at 
once attacks the hydrochloric acid, and the characteristic odour of 
enchlorine is at once perceived. If the permanganate is added with 
sufficient care to avoid local supersaturation, the appearance of this 
odour indicates with very considerable sharpness the moment when 
all the iron has been oxidised. It can, however, also be indicated 
clearly to the eye. If one or two drops of a dilute solution of pure 
ferricyanide of potassium be added to the ferrous solution so as to 
colour it blue without producing a precipitate, then on titrating 
with permanganate the disappearance of the ferrous salt is indicated 
by the simultaneous disappearance of the blue colour. This is 
illustrated in the following table. For each experiment 10 c.c. of 
ferrous sulphate solution ( a ), containing 0'0407 gramme iron, were 
acidified either with normal sulphuric acid (0*5H 2 SO 4 ) or with 
fuming hydrochloric acid (12'GHCl), diluted with water so as to 
bring the volume to about 60 c.c., then titrated with permanganate 
in hydrochloric acid solution, with the addition of enough ferricyanide 
to colour the solution blue. 
TableI. 
Number of Experiment. 
1. 
2. 
3. 
4. 
5. 
6. 
7. 
Ferrous sulphate (a), . c.c. 
10 
10 
10 
10 
10 
10 
10 
Sulphuric acid (0'5H 2 SO 4 ), ,, 
... 
... 
20 
... 
... 
... 
... 
Hydrochloric acid (12 '61101), ,, 
10 
10 
... 
25 
25 
25 
25 
Water, . . . . ,, 
30 
30 
30 
25 
25 
25 
25 
Permanganate, . . ,, 
7'55 
7'5 
7'5 
7'6 
7*45 
7-7 
7*6 
From this table it will be seen that with 10 c.c. fuming hydro- 
chloric acid the results are quite as good as with sulphuric acid. 
