Chloride and Oxygen Analysis Kit — Dean and Hawley 
109 
Foulke’s dead-stop electrometric end point 
(Foulke and Bawden, 1926: 2045 ff.), be¬ 
cause the starch iodine indicator is unreliable 
above 25° C. and our field temperatures fre¬ 
quently exceed 30° C. Essentially the same 
electrical circuit is used for both the oxygen 
and the chloride end points: only the elec¬ 
trodes are different. 
The unknown solutions are titrated with 
standard solutions from a micrometer syringe 
burette (see Trevor, 1925: 1111; Dean and 
Fetcher, 1942: 237; and Dean: unpub¬ 
lished). This burette has many advantages 
over conventional gravity-feed burettes. It is 
more compact, there is no drop error and no 
parallax error, and better than 0.1 per cent 
accuracy is possible on a total volume of 
only 1 cc. of reagent. Micro methods are 
obviously necessary to conserve reagents if a 
small apparatus is to carry enough to permit 
50 or more determinations. Two syringes 
are used interchangeably with the same 
micrometer head in this apparatus, so that it 
is not necessary to clean and refill the burette 
when changing from chlorine to oxygen 
analyses. 
DESCRIPTION OF THE APPARATUS 
All of the equipment is contained in a 
wooden box which measures 9X9X12 
inches (see Fig. 1). The electrical wiring is 
enclosed in a mahogany case which is firmly 
attached to the right-hand side of the box. 
The galvanometer is a needle type of instru¬ 
ment which has a sensitivity of 0.25 micro¬ 
amperes per scale division and a critical 
damping resistance of 1,800 ohms. 
The electrical circuit is shown schemati¬ 
cally in Figure 2. The two switches S x and S 2 
are combined in a telephone type of toggle 
switch. In the central position both switches 
are open and no current flows. When the 
switch is moved to either side, current flows 
from the battery through the series of re¬ 
sistors in the upper line. Suitable taps take 
off about 10,200 and 1,018 mv. to the Pt, 
Ag, and Standard Cell terminals respec¬ 
tively. Variations in the internal resistance 
of the dry cell can be compensated for by 
adjusting resistor R 2 when the switch is 
thrown to the left. In this position the volt¬ 
age of the standard cell opposes a fraction 
of the voltage from the battery. Resistor B 
is adjusted until no current flows through 
the galvanometer. In actual practice it has 
been found that the voltage from a flashlight 
dry cell does not change significantly, even 
when the circuit is left open for 2 days. It 
would have been satisfactory to omit the 
standard cell and variable resistor B entirely. 
The potential at the chloride electrodes could 
be checked before each series of measure¬ 
ments, as is described below. 
The electrodes are constructed as shown 
in the insert of Figure 2. Short pieces of 
silver or platinum wire are attached to stiff 
bronze wire with hard solder. The wire elec¬ 
trode is then sealed in a straight glass tube. 
It is not difficult to seal platinum into soft 
glass. Silver wire of 22 gage can also be 
sealed into soft glass but some of the seals 
break soon after sealing. After the glass is 
sealed onto the electrode wire, both the glass 
tubing and the bronze wire can be bent in 
the ordinary manner, since bronze wire 
softens at red heat. 
The stiff bronze wire is passed through a 
hole drilled in a small radio jack plug as 
indicated in the diagram. The four electrode 
leads—Ag, Cu, and two Pt—are brought to 
jacks on a mounting plate at the left end of 
the box under the end of the burette. When 
either pair of electrodes is plugged into its 
corresponding jacks, the electrode wires just 
reach the center of the titration vessel. The 
Ag and Cu jacks are further differentiated 
by color to reduce the danger of inserting an 
electrode in the wrong terminal. 
The micrometer-syringe burette consists 
of a 1.5 cc. glass hypodermic syringe fitted 
in a frame to which is attached a 1-inch 
machinist's micrometer graduated in 1,000 
parts. The burette assembly is described fur- 
