I ' 58 QUANTITATIVE AGRICULTURAL AXALYMH

I Heat about 25 gm of high-grade sodium bicarbonate in an elect ric oven

j [ to 300° for three to five hours. A platinum dish is bc'.st for this purpoHf*.

I < Cool the product in a desiccator and preserve in a tightly .stoppered hot lie.

! ], ' On a counterpoised glass weigh exactly 5.300 gm of the pure sodium car-

' ' bonate. Brush this into a dry funnel which rente in the nerk of a 5(X)-n;

I \ volumetric flask. Jar most of the salt into the iia.sk and rin.se down the

J | , remainder with distilled water. Remove the* funnel, gently agitate until

' the carbonate is dissolved, then dilute to the murk and rt.ix well.

* Titration. — Fill two burettes with the respective solutions. Before

; \ • proceeding with the titrations, practice reading t he color changes a,s follows:

1 f , Place 100 cc of distilled water in a beaker and add a drop of methyl orange

! and 0.5 cc of carbonate solution. Drop in acid until'! he last drop changes

! ' the tint from yellow to pink. Now, drop in carbonate solution until tin?

'l yellow color reappears. Repeat the process until the color change can be

4 » observed when but one drop of cither solution is added. It will aid in thcs

J next process if this solution is preserved and another prepared, the two

I showing the two colors of methyl orange. These are set asid<* for comparison.

"t Measure out exactly 25 cc of the sodium carbonate .solution into a

; beaker or Erlenmeyer flask, placed on a white, surface. Add a drop of

I ' methyl orange and then carefully run in add solution from the other burette

I f until one drop changes the color from yellow to pink. Record t he volume of

' I acid required to do this. In case the end point, has been overstepped,

t I add 5 cc more of the carbonate solution to that already in the fla*k and

[ I ; < continue the titration. Finally record the volumes of both carhoimte and

I acid.
I

f I Since the carbonate solution was exactly fifth-normal, 1 «'<• is equivalent to

! < 0.007294 gm of hydrochloric acid. The concentration fin grains of H( 1 per
cubic centimeter) of the titrated solution IK then " '"'' ••*» where \'f
and Va are the volumes of carbonate and «cid, rcHpectively,

t ,t ,., , .., . . . t . . * .

to each other, and that of the original sample IH ' , r » where *S*

* S \r a

is the volume of sample used for the dilution. Gmwn />*r ruhir crnltmHcr
may be converted into per cent by waif/hi by dividing by tin* specific gravity
of the sample, measured at 20°. The nvnrutlUy of the* titrated ncid solu-

tion is obtained, if desired, as in the case of «ilver nit rate Miiliif ion : ^ • 'r ...•<
normality, Fa being the volume of acid equivalent to 25 re of t In- lift h-nor »i«I
carbonate. For the original sample, normality - 1CX^ f^,2r>N .

Volumetric, by Titration with Potassium Hydroxide. In
the number of determmation.H of hydrochloric arid to !M* umd
small, no advantage is gained by Urn UHCJ of standnnl |
hydroxide. This m bccaunc th<» most sttfisfacfory nwtliod for
Rtandardimtion of this nolution is by fitrafion apiinsf. an ari«I

o n