112 
PACIFIC SCIENCE, Vol. 1, April, 1947 
holds five 60-cc. screw top bottles and two 
10-cc. screw top vials. In addition, there are 
several larger reagent bottles in the bottom 
of the box and a bottle of distilled water for 
washing electrodes and glassware. A glass 
tumbler is fitted under the electrodes for a 
waste jar. A rubber ear syringe is fitted with 
a glass delivery tip bent at an angle of 135°. 
This syringe can be filled from the distilled 
water bottle and the water in it then directed 
in a stream into the inverted titration vessel 
or onto the electrodes to clean them. 
The reagents are all contained in screw 
cap bottles or vials. The screw caps are lined 
with Polythene, which is resistant to all the 
reagents used in this work. Two of the vials 
are fitted with rubber disks from 10-ml, 
penicillin bottles. The disks are held on by 
screw caps which have been drilled with 
14-inch holes. The rubber disks on the vials 
can be repeatedly perforated by a hypo¬ 
dermic needle and the reagents withdrawn 
through the needle. 
All the reagents and equipment used for 
the chloride analysis are marked with black 
paint and the various reagents are identified 
by white letters on the top, as well as by con¬ 
ventional labels on the sides of the bottles. 
The reagents and apparatus for the oxygen 
determination are likewise marked with red 
paint and white letters. The metal parts of 
the syringe pipettes and the burette are of 
brass which was first dulled by a dip in silver 
nitrate and nitric acid, and then coated with 
Glyptal varnish which was baked on. This 
treatment produces a non-glaring, corrosion- 
resistant surface. The syringes are attached 
by clips to the inside of the top of the box. 
A small box of filter paper squares, about 3 
cm. on a side, which are used to wipe the 
burette tips and the electrodes, is also at¬ 
tached inside the top of the box. A rubber 
stopper is screwed inside the top at the right- 
hand side in such a way that the lid will not 
close until the switch has been turned off. 
This arrangement insures that the battery 
will not be left on when the box is closed. 
CHLORIDE ANALYSES 
The chloride analysis depends upon the 
fact that the potential of a silver electrode 
changes rapidly when all the chloride ions 
have been precipitated by silver ions. Since 
it is impossible to measure a single electrode 
potential, another electrode which is not 
sensitive to chloride ions must be present to 
complete the circuit. We have used a copper 
electrode in the presence of nearly saturated 
copper sulfate. The potential between these 
two electrodes is about 200 mv. at the end 
point. The potentiometer circuit supplies 
200 mv. between the Cu and Ag electrodes 
and, at the end point, no current will flow 
through the galvanometer. 
Before the end point is reached the poten¬ 
tial between the electrodes will be less than 
200 mv. and the galvanometer will be de¬ 
flected to the right. There is a large protec¬ 
tive resistance in series with the chloride 
electrodes so that the galvanometer may be 
left continuously in circuit. As the end point 
is approached the galvanometer needle ap¬ 
proaches £ero and is deflected to the left as 
soon as the end point has been exceeded. 
The deflection produced by the addition of 
one or two burette divisions of silver nitrate 
is greatest at the end point. This fact can be 
used to set the potentiometer to the cor¬ 
rect potential. The potentiometer is adjusted 
until the galvanometer indicates zero. The 
galvanometer deflection is then noted after 
the addition of two burette units of silver 
nitrate. This procedure is repeated until the 
galvanometer deflection is a maximum. The 
potentiometer is left at this setting for sub¬ 
sequent titrations. 
The silver nitrate reagent contains 4 per 
cent silver nitrate and 0.5 per cent nitric 
acid. The burette is filled by bringing the 
reagent bottle of silver nitrate, marked with 
a T on a black screw cap, up under the 
burette tip. The plunger of the syringe is 
withdrawn by unscrewing the micrometer, 
and silver nitrate is sucked into the syringe. 
