Chloride and Oxygen Analysis Kit — Dean and Hawley 
Any air bubbles are displaced by rotating the 
burette in its clamp until the tip is upwards 
and then forcing a little of the silver nitrate 
reagent out of the tip. The burette is filled 
up to the 1,000 mark on the micrometer 
and the tip rinsed with water. 
Ten cc. of saturated copper sulfate is 
placed in the titration vessel; a syringe with 
tip broken off is used to make the transfer. 
Commercial bluestone can be used for this 
solution, although it may introduce an un¬ 
desirably high blank. Reagent grade copper 
sulfate is perfectly satisfactory. The copper 
sulfate solution is placed under the elec¬ 
trodes and the air stirrer is started. A small 
residual concentration of chloride ions may 
produce a galvanometer deflection to the 
right. If it does, silver nitrate is added until 
the galvanometer reads zero. The burette 
reading is recorded. The chloride sample, 
about 0.4 cc., is then introduced from a 
precision syringe pipette (Krogh, 1935: 
130; Dean: unpublished). Silver nitrate is 
added until the galvanometer again indicates 
zero and the second burette reading is 
recorded. 
Neither the exact volume relations of the 
syringes nor the concentration of the silver 
nitrate need be known exactly. All these are 
evaluated as a single factor by titrating the 
same volume of a known standard solution 
of sodium chloride which contains exactly 
20 gm. of chloride ions per liter. 
When the galvanometer has been brought 
to zero a second time and the burette read¬ 
ing has been recorded, the air stirrer is re¬ 
moved and wiped. The burette is tipped up 
and the tip is wiped and the burette is re¬ 
filled. The electrodes and the burette tip are 
rinsed and the apparatus is ready for the 
next determination. 
The errors are of the order of 1 burette 
division or 1 part in 800. Greater precision 
could be obtained by precipitating most of 
the chloride in a larger sample with silver 
nitrate from another pipette. A more dilute 
113 
solution of silver nitrate could then be used 
in the burette. It might be advisable to carry 
out such determinations in more dilute solu¬ 
tions to avoid too much clumping of the 
silver chloride precipitate. The accuracy is 
limited by the reproducibility of the syringe 
pipettes. Krogh (1935: 130) reports an 
accuracy of 1 part in 10,000 and we have 
several syringes with an accuracy of 2 parts 
in 10,000. 
OXYGEN ANALYSES 
Oxygen is determined by its reaction with 
a solution of manganous hydroxide to form 
manganic oxides. When all the oxygen has 
been absorbed, the solution is made acid 
and the manganic ions react with iodide ions 
to liberate free iodine. The iodine is titrated 
with sodium thiosulfate in the presence of 
two bright platinum electrodes. A potential 
of 10 mv. is applied between these electrodes 
and a current will flow as long as there is 
iodine in the solution to remove electrons 
from the negative electrode. As soon as all 
the iodine has been removed the current 
ceases to flow, except for a very small resi¬ 
dual current. As the end point is approached, 
the galvanometer deflection decreases from 
the left and the end point is taken when the 
galvanometer indicates one unit deflection to 
the left. 
A 10-cc. syringe pipette (Krogh, 1935: 
132; Dean: unpublished) is fitted with a 
2-inch 18-gage stainless steel needle. An 
aluminum cam cemented to the plunger with 
Varno cement will engage a stop on the 
side of the syringe holder when the syringe 
holds 10 cc. An additional 0.2 cc. can be 
introduced by rotating the cam away from 
the side stop and pulling back until the 
plunger reaches an end stop. 
The syringe is first rinsed with Solution I. 
This solution is made up by dissolving 90 
gm. of Nal and 40 gm. of NaOH in 55 cc. 
of water (Pomeroy and Kirschman, 1945: 
716) and all air bubbles are expelled. This 
