56

QUANTITATIVE AGRICULTURAL ,l.\M/,r,S7X

point at the prevailing temperature. A tenth-normal solution
of this gas, has aP// value of about 3.75, from the small amount
of weakly ionized carbonic acicl existing in the solution. Mom
concentrated solutions, such as might be produced by temporary
supersaturation, will have somewhat lower /•*// values but thc*y
will usually fall within the color range of methyl orange, whieh in
2.9 to 4. It is therefore convenient to titrate a weighed .sample
of sodium carbonate, dissolved in water, to an end point wil.li
methyl orange, this representing complete decomposition of the
carbonate. In this case the hydrogen equivalent of sodium car-
bonate is 2, since both univalent sodium atoms are replaced by
hydrogen. Its equivalent weight is therefore 4> • />3, while
that of hydrochloric acid is 36.468, as usual.
These points will be made clearer by reference to Pig. 1, page
14.
The determination above discussed is introduced here as an
example of a method for determining the concentration of
any hydrochloric acid solution. The analysis of nuch a solution
is expressed as grams per cubic centimeter or as per c-cni //// */v7f////.
However, it should be remembered that the method will apply to
similar determinations of concentration of other strong acids,
such as sulphuric and nitric acids. Also it is a much uned
method for standardizing volumetric acid .solutions, in which
case the result of the experiment is expressed either in normality
or in terms of the weight of some other element, or group of
elements equivalent to 1 cc as explained on page H and an
discussed in connection with standard silver nitrate* solution,
above. This method for standardizing hydrochloric acid i»
described on page 83, for the analysis of carbonate*.
Volumetric Determination: Sodium Carbonate Method......-Thf laboratory
stock of "dilute" acid in suitable for thi« ttx«rr«c», or a Hatupii* may h«
furnished by the instructor. Calculates the dilution nwMwiry to iititki* tint
solution approximately fifth-normal, If anything « known regarding th«*
approximate concentration of the sample. If then* "w no avaiiuhlr infor-
mation on this point determine the specific gravity with a floating hydrom-
eter (see page 97) and calculate the approximate concent nit ion from thi?
following table.