100 c.c. are equivalent to 1.27 gram of iodine.
This solution is standardised by weighing, in a small beaker, about half
a gram of iodine, to which is added a crystal or two of potassium iodide
and a few drops of water. When dissolved, the solution is diluted to 100
c.c., and titrated in the manner described. The starch solution is made
in the manner described under the iodide copper assay. 5 c.c. are used
for each titration.
In determining the effects of variations in the condition of the assay a
solution of iodine was used, which was equivalent in strength to the
"hypo" solution. It was made by dissolving 12.7 grams of iodine with 25
grams of potassium iodide in a little water and diluting to 1 litre. 100
c.c. of this solution were found (at the time of the experiments) to be
equivalent to 102.0 c.c. of the "hypo."
~Effect of Varying Temperature.~--The bulk of the solution was 100 c.c.;
20 c.c. of iodine were taken, and 5 c.c. of starch solution were added
towards the end as indicator. These conditions are also those of the
other experiments, except where otherwise stated. Iodine being volatile,
it is to be expected that with hot solutions low results will be
obtained.
Temperature 15° 20° 40° 60° 80°
"Hypo" required 20.4 c.c. 20.4 c.c. 20.1 c.
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