MICHIGAN ACADEMY OF SCIENCE. 
121 
THE OXYGEN CONTENT OF THE WATERS OF DOUGLAS LAKE, 
MICHIGAN. 
BY DAVID A. TUCKER, JR. 
The analysis of the oxygen and carbon dioxide content of the waters 
of Douglas Lake was undertaken during the summer of 1912 at the 
suggestion of Professor Jacob Reighard. Owing to delays in the 
shipping of chemicals and apparatus the work was somewhat interfered 
with. The investigation of the pxygen content was much more com- 
plete than that of the carbon dioxide content. 
Douglas Lake is in Cheboygan County, Michigan. It has an area 
approximately of twenty-two square miles, being shaped something like 
a fish with the median longitudinal axis running in a N.W.-S.E. direc- 
tion. Of the various parts of the Lake the deepest portions, as shown 
by the soundings of the engineering students of the University of 
Michigan, are in the so-called South Fish-Tail Ba} r — on the shores of 
which the Biological Station is situated. The greater number of samples 
were taken from this Bay. 
The samples of water were obtained by means of a clock-pump from 
the various levels. For the collection Magnesium citrate bottles with a 
capacity of 385 cc. were used. These could be pumped full of water 
and then tightly stoppered. Some difficulty was encountered in getting 
the pump airtight in order to avoid any change of the gaseous con- 
tent while being taken. The pump and hose were always thoroughly 
flushed with water at the given level before the sample from that level 
was taken. It is quite probable that the receiving hose while lowered 
to a definite depth actually carried water up from a stratum of a foot 
thick, or even more on days when the boat was rocked by the wind. 
The temperatures at different depths were recorded by maximum and 
minimum thermometers. 
The estimation of the oxygen content was made by an iodometric 
method — the same as used by Birge in similar investigations of the 
waters of Wisconsin Lakes. To each bottle of water 1 % cc. of MnCL 
solution was added by means of a pipette which reached the bottom 
of the bottle. An equal quantity of NaOH-KT solution was then added, 
resulting in the precipitation of Mn (OH) 2 which was shortly oxidized 
by the Oxygen dissolved in the water; the process being indicated by 
the change in the color of the precipitate from white to brown. After 
the precipitate had settled to the bottom, 3 cc. of concentrated HC1 was 
introduced just above the precipitate, which, acting on the Mn(OH) 4 
resulted in the formation of MnCL and the liberation of clorine. 
This latter substance reacting with the KI gave free Iodine. The 
amount of Iodine set free being porportional to the quantity of 
oxygen dissolved in the water. The Iodine was determined by titration 
against a standard solution of sodium thiosulphate. 
The following formula from Birge was used in the calculation of the 
numerical results: 
