122 
FIFTEENTH REPORT. 
(1) Oxygen in ec. per liter = 
0.05S25 n x b x 1,000. 55.825 bn 
v x n 1 n*v 
In this formula b — the number of cc. of potassium dichromate 
solution used in standardizing the sodium thiosulphate, i.e. 25 cc. ; n 1 = 
the number of cc. of thiosulphate used in standardization against the 
dichromate ; n = the number of cc. of thiosulphate required for the 
sample of water. 
By means of a table showing the number of cc. of oxygen required to 
saturate one liter of water at various temperatures, the percentage of 
saturation was calculated. 
The strengths of the solutions used are shown as follows: 
MnClo — 200 grs. of the salt, free from iron, dissolved in water and 
diluted to 250 cc. 
NaOH-KI — 180 grs. of NaOH and 75 grs. of Ivl dissolved in water 
and diluted to 500 cc. 
HC1 — Concentrated, chemically pure. 
Sodium thiosulphate — approximately N/100. 
Potassium dichromate — accurately N/100. 
Starch indicator was used in the titration of the iodine. 
The samples were in every case analysed within four hours after 
the collection. The experiments of Birge indicate that no loss of oxygen 
results in this time. 
The results of the analyses for the depths 0, 3, 5, 10, 15 meters and 
the bottom are plotted so that the vertical spaces represent the cc. of 
oxygen per liter and the horizontal spaces indicate the time at which 
the observations were made. At the beginning of the observations, July 
13, the oxygen content at the surface was a little over 7.2 cc. per liter 
while at three and five meters the quantity was about 6.8 cc. At ten 
meters 4.6 cc. per liter were found at 15 meters 3.3 cc. per liter, while at 
the bottom there was only 0.0 cc. per liter present. During the next 
three days, 13th to the 16th there was a decrease of about 0.3 cc. per 
liter at the surface and the 3. 5 and 10 meter levels. The quantity at 
15 meters dropped 26 cc. per liter while only a trace was found at the 
bottom. From the 16th to the 18th there was an increase at the surface 
of about 0.45 cc; the oxygen at 3 and 5 meters decreased slightly, be- 
tween 0.2 and 0.3 cc. so that on the 18th the water at these depths con- 
tained the same amount of oxygen, namely about 6.6 cc. per liter. At 
10 meters 4.7 cc. were present while there was little change at the 15 
meter level. From the 18th to the 22nd the surface waiter lost only a 
fraction of a cubic centimeter, while at 3 and 5 meters there was a de- 
crease of some 0.8 cc. But little change took place at 10 meters. At 
15 meters, however, a marked loss of oxygen w r as found. A trace of 
oxygen was found at the bottom on the 19th but none at all on the 22nd. 
During the two days — 22nd to 24th — the surface content was lowered 
one cc. ; that at 3 and 5 meters one-half cc., that at 10 meters a frac- 
tion of a cc. while at 15 an increase of 0.8 cc. was noted. A trace of 
oxygen was found at the bottom. During the period from the 24th to 
the 31st the surface content remained quite uniform; an increase in 
oxygen at the three meter level of 0.6 cc. occurred; a decrease of 0.6 
