114 
PACIFIC SCIENCE, Vol. 1, April, 1947 
reagent is kept in a small rubber-capped vial 
marked on each side with one white dot. 
The needle of the syringe is inserted into 
the vial and the vial is inverted while the 
solution is drawn in and the air bubbles are 
expelled. This leaves about 0.1 ml. of solu¬ 
tion in the dead space of the syringe. The 
water sample is then drawn into the syringe 
until the cam on the plunger reaches the side 
stop. The needle is then inserted into a 
second vial, marked with two white dots, 
which contains Solution II. This solution is 
made from 40 gm. of MnCl 2 , 10 cc. of 
6N HC1, and enough water to make 100 cc. 
This solution is drawn into the syringe by 
moving the plunger from the side to the end 
stop. 
The manganous chloride reacts inside the 
syringe with the sodium hydroxide which 
was left in the dead space, to produce a light 
fluffy precipitate of manganous hydroxide. 
This precipitate absorbs oxygen, and in 4 
minutes substantially all of the oxygen will 
have been absorbed. The contents of the 
syringe are then discharged below the sur¬ 
face of 1 cc. of 6N HC1 in the titration 
vessel. The syringe is rinsed first with the 
acid solution to dissolve any manganous 
hydroxide remaining in the syringe, and then 
with two small portions of water from a 
spare titration vessel. The 6N HC1 is con¬ 
tained in a 60-cc. bottle fitted with a rubber 
medicine dropper. One dropper full is about 
1 cc. 
The titration vessel now contains iodine 
equivalent to the oxygen which was present 
in the water. The iodine is titrated with a 
sodium thiosulfate solution. This solution 
must be made up fresh every week by dilut¬ 
ing to 60 cc. one medicine dropper full of 
a 60 per cent solution of sodium thiosulfate 
containing 1 per cent borax. This concen¬ 
trated solution is quite stable. Most of the 
iodine is discharged with thiosulfate from 
the burette before the air stirrer is started, 
because the air might otherwise remove some 
of the iodine. 
The thiosulfate solution and the volume¬ 
tric apparatus are standardized by the use of 
a standard solution of KI0 3 . This solution 
is 0.0004167 molar and is equivalent to 
14 cc. (STP) of oxygen per liter. The dead 
space of the syringe is first filled with Solu¬ 
tion I. The syringe is then rinsed with acid 
contained in the titration vessel and filled 
with the standard iodate solution. The iodate 
reacts with the iodide and acid to liberate 
iodine in the syringe. The iodine is titrated 
with thiosulfate, and the burette difference 
which is found corresponds to 14 cc. of 
oxygen per liter. Blank runs on water which 
had been freed of oxygen by hydrogen and 
platinized asbestos showed that the end 
point and other errors are less than 0.1 cc. 
of oxygen per liter. 
The oxygen concentration is calculated in 
essentially the same manner as that used for 
the chloride. The initial burette reading is 
always taken as 1,000. This procedure in¬ 
troduces a small constant error of the order 
of magnitude of 0.1 cc. of dissolved oxygen 
per liter. 
SUMMARY 
A portable apparatus which is equipped 
for the determination of chlorides and dis¬ 
solved oxygen in pond waters is described. 
The chloride is determined by a new elec¬ 
trometric method. Oxygen is determined by 
a modified Winkler method and the iodi- 
metric end point is detected electrometrically. 
The volumetric apparatus consists of preci¬ 
sion syringe pipettes and a micrometer 
burette. Up to 25 gm. of Cl per liter can be 
determined with an accuracy of 0.06 gm. 
per liter. Up to 20 cc. of dissolved oxygen 
per liter can be determined with an accuracy 
of 0.1 cc. per liter. Greater precision over a 
smaller range of chloride concentration is 
possible, since the syringe pipettes can attain 
an absolute accuracy of one part in 10,000. 
