THEORY AND GENERAL PRINCIPLES 5

hydrochloric acid, a drop or two of an appropriate indicator,
as methyl orange or methyl red, being added to show the end
point of the reaction.

If V = cubic centimeters of standard solution required, C =
concentration of standard solution (gm of HC1 per cc), S — gm of
sample used, Eq^cl — equivalent weight (see page 7) of hydro-
chloric acid (36.468), and EqNaOU = equivalent weight of sodium
hydroxide (40.008), then

V C = gm HC1 used, (1)

^4r^^ = gm NaOH in sample used, (2)

•&#HCI

100 V C EQNf.01g: . ,.,. X-XTT • T /ov

- ^^ — ^£££E _ per cen£ NaOH m sample. (3)

O -£#HCl

Of course this derivation is based upon the assumption that
sodium hydroxide is the only basic substance present in the
sample.

As in gravimetric analysis it is convenient to collect all of the
constants of the final expression. For all determinations of
sodium hydroxide that are made by means of this particular
standard solution of hydrochloric acid, V and S are the only
variables. The quantity:

"Eqav 36.468
may be called the "base factor" of the acid. This can then be
simplified and recorded upon the label of the bottle. Let this
be designated by FB. Thereafter, so long as this solution is used
for the determination of sodium hydroxide in other samples, the
calculation of the results of titrations will be made by means of
the equation:
100 V FB . TV T ^-o- ,.N
- — £_ =per cent NaOH. (4)
AJ
If the same standard solution is to be used for the determination
of any other base it will be necessary to recalculate the value for
FB for this substance and to use the new value in an equation
similar to Eq. (4). If a new standard solution of a different
concentration is prepared, or if the concentration of the original
standard has changed, a new value for FB is calculated.