I

01

a 1 *

will be seen from relations (a) and (6)

Weights.—If the rule given on page 6
f/»r M.akirii* rh- him tit reading a percentage reading is followed
wb**!i IMIIC th' rormal system, the result is the volumetric factor
of sample. This, of course, becomes one-tenth of the gram-
oquivalont of the element or compound determined in the sample.
System.—A further simplification may be made by
adjusting the standard solution until each cubic centimeter is
equivalent to a simple fraction of a gram of the substance to be
titrated, instead' of to a simple fraction of a gram-equivalent
as in the normal system. One cubic centimeter of a standard'
iodine solution might then be equivalent to 0.005, 0,002, 0.001,
etc., gm of sulphur. This results in a very much simplified cal-
culation and a further saving of time is accomplished by using
a sample weight which bears a simple relation to the equivalence
of the standard. In the case just noted the sulphur sample
might be used in portions of 0.5, 0.2 or 0.1 gm, or of ten times
these weights. Then 1 cc of standard solution would indicate
1. per cent or 0.1 per cent of sulphur.
Such solutions as these are frequently made for technical work
in industrial laboratories, where large quantities of standard
solutions are required for the titration of a single constituent of a
large number of samples. Mention may be made of the use of
potassium permanganate or potassium dichromate solutions for
the titration of iron in ores, of sodium thiosulphate for the titra-
tion of copper in ores or available chlorine in bleaching powder
and of potassium ferrocyanide for the determination of zinc.
In fact any standard solution may be made in this system and it
be so made if its use is to be limited to the determination of
one substance.
Standardization.—Thus far we have dealt only with the calcu-
lation of the results of volumetric analysis, assuming that the
standard solution was ready for use in the experiment. The
determination of the exact concentration of the standard solution
is called "standardization." The details of the experimental
work will be treated later and will be mentioned here only so
far as they may serve to illustrate the methods used in the
calculations.