71 
how much permanganate is equal to the ferrous sulphate 
solution, and knowing the “ oxygen value ” of the perman- 
ganate solution, it at once furnishes me with the “ oxygen 
value ” of the ferrous sulphate solution. 
Next I take a known volume of the chromic acid solution 
and titrate it with the standard ferrous sulphate solution, 
until all the chromic acid is reduced, a point easily seen 
with a little practice as the slightly yellowish green colour 
at the final stage of the titration changes sharply to a bluish 
green on the addition of one drop, and one further, at this 
point using a solution of ferricyanide of potassium as an 
indicator, it is seen that there is a very slight indication of 
excess of ferrous sulphate present, whereas before the ad- 
dition of this drop there was no such indication. This 
operation furnishes the value of the chromic acid solution 
expressed as ferrous sulphate solution. 
The chromic acid solution will keep a very long time, but 
it is advisable to prepare the ferrous ’sulphate solution 
freshly at least once a week. 
Having prepared the standard solutions the process of 
analysis is as follows, viz. : — 
Determination of the organic carbon. 
Place 250 c.c. of the water sample in the “boiling fiask,” 
of 16 oz. capacity, add 100 c.c. of the chromic acid solution, 
and 10 c.c. of strong sulphuric acid, and boil for about 
thirty minutes, when the oxidation of the organic matter is 
complete, the water in the “ boiling-flask ” having become 
perfectly clear. I then dilute the contents of the flask .to 1 
litre, and take out 100 c.c. of this solution and titrate it 
with the standard ferrous sulphate solution until there is a 
very slight excess of the latter. By calculation I find how 
much carbon, the oxygen thus indicated, is equal to. 
Determination of the organic nitrogen. 
Contrary to expectation I found that the nitrogen in 
organic compounds is converted into ammonia and not into 
