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 .
o 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