i'LTI'L\lL AXALYS1S

of Weight— The volumetric
itiidy * '\plahied liave been made upon the assumption th^"t trie
;ipV * *':nlt *»\a*» not adjusted to any particular value altti-O^g11
wit*-, < )+h uniiM\ accurately determined. In Eq. (4) F& 1S a
-tunt t\»r this particular standard solution in this parti «3U»lar
ut'tt nnniiitiuL. Thtrefore if some care is exercised in adj u^kmg;
the MimpV weight, K so that it will bear some simple relation* tx>
/"/. the emulations will be materially simplified. For
if S is niadt to equal 100 F^ Eq. (4) will become:
F = per cent XaOH.
That is, each cubic centimeter of standard solution used iix
lit uit ion represents a weight of sodium hydroxide which
per cc*nt of the sample weight, so that the burette reading
a percent :igo reading. From this the rule follows:
To make tfa burette reading a dire-ct percentage reading,
sa^iplc ic c:gM equal to 100 FB*
In practice it often happens that such an adjustment calls for
a too small weight of sample and it does not then provide for
sufficient accuracy. Ten or one hundred times this weigh. -t is
often taken, making 1 cc of standard solution indicate tent;lis
or hundredths of 1 per cent.
Use of Aliquot Parts. — -If the adjustment of sample we
must be with a high degree of accuracy it may be that
extra time involved in the adjustment will not be compensa/fced
by time saved in calculations, in which case such adjustiraejat
will not be desirable. But if relatively large samples may be
used for the analysis an error in weighing becomes of proportion-
ately less importance and adjustment may be made more rapidly
less carefully. These considerations apply as in gravimetric
analysis (page 4).
The use of large samples is rendered practicable by the uso of
the principle of aliquot parts. Some simple multiple of -fclxe
required weight is taken and the solution is diluted to a definite
volume in a volumetric flask and well mixed. A definite fraction
of this solution is taken for the analysis and the proper factor ~fco
correct for this is used in the calculation of results. For example,
If a degree of accuracy carried to the fourth decimal place ' is
required in weighing 0.3943 gin for a single analysis, ten tiin.es