NORTHWESTERN LAKES OF THE UNITED STATES. 
61 
DETERMINATION OF CARBON DIOXIDE BY SEYLER METHOD. 
This method (Seyler, 1894) has been used as on the Wisconsin lakes. 
SOLUTIONS REQUIRED. 
1. Phenolphthalein. — Dissolve 1 g. in 200 cc. of 50 per cent alcohol. 
2. Methyl orange. — Dissolve 0.2 g. of the powder in 200 cc. of distilled water. 
3. N 144- sodium carbonate. — This solution is the standard by which the hydro- 
chloric acid is prepared, so should be made with great care. Dry the purest 
N a 2 C0 3 just below the fusing point (best by placing a platinum crucible inside a 
porcelain crucible and heating for 30 minutes over a M6ker burner) , cool, and weigh 
0.12045 g. ; dissolve it in carbon-dioxide-free water and make up to 1 liter in a stand- 
ardized flask. This solution is then checked by titrating with a N/44 hydro- 
choloric acid solution standardized with Sorensen’s sodium oxalate which has been 
dried at 130° C., weighed, then ignited to sodium carbonate. 
4. N/44 hydrochloric acid. — Add chemically pure hydrochloric acid to carbon- 
dioxide-free distilled water until it exactly titrates the above N/44 Na 2 C0 3 , using 
methyl orange as indicator. 
The solutions were also checked against N/100 H 2 S0 4 solution, the H 2 S0 4 
content having been determined gravimetrically. 
It is important that carbon-dioxide-free distilled water be used for both acid 
and alkali solutions. If the water contains carbon dioxide, the phenolphthalein 
and methyl orange titrations will not agree. The water is distilled and collected 
in Jena or similar hard glass flasks, in which it is boiled for three hours while a slow 
stream of carbon-dioxide-free air is bubbled through it. 
The N/44 sodium carbonate solution is stored in 500 cc. hard glass bottles with 
the glass stoppers sealed in, and the N/44 hydrochloric acid is placed in similar 
1-liter bottles. These solutions are exposed to the air as little as possible and are 
checked against each other every few days. A new bottle is opened once a week. 
TITRATION FOR FREE CARBON DIOXIDE. 
Measure 100 cc. of the water with a pipette into a tall beaker such as is used 
for the electrolytic determination of copper (about 110 mm. high, 47 mm. diameter 
at the bottom, and 65 mm. at the top). Add three drops of phenolphthalein solu- 
tion. If it turns a very faint pink, the water is neutral and contains half-bound 
C0 2 equal to the fixed. If colorless, it is acid, containing an excess of C0 2 , and is 
titrated with N/44 Na 2 C0 3 , stirring well until a faint pink color persists for three 
or four minutes. If the sample becomes pink when the phenolphthalein is added, 
it is alkaline and has less half -bound C0 2 than fixed. It is titrated with N/44 
HC1 until the pink color just persists. 
If the water contains much free C0 2 , some is lost during the titration in an open 
beaker. Few of these samples were encountered on these lakes, but during the 
summer of 1913 all C0 2 titrations were carried out in 100 cc. calibrated glass-stop- 
pered flasks with a 25 to 30 cc. bulb blown in the neck above the calibration as used 
by Tillmans and Heublein (1911) . The use of these flasks may require a little more 
time than stirring in beakers, but it is believed that all end points are more easily 
determined. The loss of C0 2 and loss by spattering are entirely eliminated. 
