58 
bulletin of the bureau of fisheries. 
divided into two lots, one of which was always used for oxygen samples and the 
other for carbon dioxide, because the acid used in the oxygen bottles alters the 
carbon-dioxide titration. 
METHOD OF TAKING SAMPLES. 
These samplers have been used for taking all the samples in this work, except 
as noted, and have proved satisfactory in every way. In use the sampler is set open 
with the pinchcocks closed and is lowered slowly to the required depth by means 
of a calibrated line. The messenger is then dropped, closing the sampler, which is 
then drawn to the surface. It was at first thought best to churn the sampler up 
and down before dropping the messenger, but numerous tests showed that better 
results were obtained, especially at the bottom and in the thermocline, by lowering 
the apparatus slowly and dropping the messenger as soon as the required depth 
was reached. 
When the apparatus is brought to the surface, the upper pinchcock is removed 
and the oxygen bottles rinsed three times with a small quantity of water drawn 
from the lower tube. Each bottle is then filled by placing the tube ( H ) at the 
bottom and allowing the bottle to fill slowly to overflowing. The tube is then 
slowly withdrawn while flowing and the snap stopper closed so that there are no 
air bubbles in the bottle. The carbon dioxide sample is then taken similarly, 
except that an air bubble is left below the stopper. 
METHODS OF ANALYSIS OF SAMPLES. 
The methods used in determining the dissolved oxygen and the carbon dioxide 
are the same as those used by the Wisconsin Geological and Natural History Survey 
on the Wisconsin lakes, except for a few changes in manipulation. All results 
have been calculated and stated as in the Wisconsin report, so that they may 
easily be compared. 
DETERMINATION OF DISSOLVED OXYGEN BY WINKLER METHOD. 
The Winkler method (Winkler, 1888) was used for determining the dissolved 
oxygen. 
SOLUTIONS REQUIRED. 
1. Manganese chloride. — Dissolve 200 g. of c. p. manganese chloride in distilled 
water to make up to 500 cc. 
2. Potassium hydroxide and potassium iodide. — Dissolve 180 g. of potassium 
hydroxide (pure by alcohol) and 75 g. of chemically pure potassium iodide. Make 
up to 500 cc. Sodium hydroxide may be substituted for potassium hydroxide. 
All must be free from nitrites which would liberate iodine. 
3. Hydrochloric acid. Concentrated chemically pure. 
4. Sodium thiosulphate. — This solution was prepared in the field by adding 6 g. of 
chemically pure crystallized sodium thiosulphate (Na 2 S 2 0 3 5H 2 0) to a one-half-gallon 
jug of soft water. This solution was then standardized against potassium bichro- 
mate and checked every two or three days. Sodium thiosulphate is standardized 
as follows: 
