70 
in this particular instance failed to estimate the amount of 
carbon present by l‘t'51 per cent. I have found, however, 
in some cases that it expresses fairly well the amount of 
organic carbon present in a water, but it cannot be safely 
relied upon to do so. 
I will pass from this part of the subject to the modifi- 
cation of my process which I have arrived at after consider- 
able experiment and expenditure of time. 
The principle of my first process consisted in the oxidation 
of the carbon in the water to carbon dioxide, this being 
affected at the expense of the chromic acid, consequently 
the latter must be reduced to a lower oxide of chromium 
during the process. Bearing this fact in mind I at last 
concluded that a determination of the amount of oxygen 
given off by the chromic acid to the carbon must necessarily 
give me the equivalent to it of carbon in the water. The 
reaction which occurs on adding a solution of chromic acid 
in water (acidulates with sulphuric acid) to water containing 
organic matter is as follows, viz. : 
4 Cr 03 + 6S04H2 + 3C - SCOa + 2Cr 2(S04)e + 6 H 2 O. 
As an excess of chromic acid is always used in the process 
all that is therefore necessary is to estimate the amount of 
chromic acid still remaining unreduced, by means of some 
convenient standard solution, which is itself oxidised by the 
excess of chromic acid. In order to carry out the process I 
first prepare the necessary standard solutions. 
Preparation of the standard solutions. 
1 st. Ordinary decinormal permanganate of potassium 
solution (3T6 grams to 1 litre). 
2nd. A solution of pure chromic acid in pure distilled 
water (about 10 grams to the litre). 
3rd. A solution of ferrous sulphate in pure distilled 
water (about 25 grams to the litre). 
First I titrate the ferrous sulphate solution by means of 
the decinormal permanganate solution and find in this way 
