~Test Paper.~--The test paper is prepared as follows:--45 grains (2.9
grms.) of white maize starch (corn flour), previously washed with cold
water, are added to 8-1/2 oz. of water. The mixture is stirred, heated to
boiling, and kept gently boiling for ten minutes; 15 grains (1 grm.) of
pure potassium iodide (previously recrystallised from alcohol, absolutely
necessary) are dissolved in 8-1/2 oz. of distilled water. The two
solutions are thoroughly mixed and allowed to get cold. Strips or sheets
of white English filter paper, previously washed with water and re-dried,
are dipped into the solution thus prepared, and allowed to remain in it
for not less than ten seconds; they are then allowed to drain and dry in a
place free from laboratory fumes and dust. The upper and lower margins of
the strips or sheets are cut off, and the paper is preserved in well-
stoppered or corked bottles, and in the dark. The dimensions of the pieces
of test paper used are about 4/10 inch by 8/10 inch (10 mm. by 20 mm.).[A]

[Footnote A: When the paper is freshly prepared, and as long as it remains
in good condition, a drop of diluted acetic acid put on the paper with a
glass rod produces no coloration. In process of time it will become
brownish, when treated with the acid, especially if it has been exposed to
sunlight. It is then not fit for use.]

In Germany zinc-iodide starch paper is used, which is considered to be
more sensitive than potassium iodide.

~Standard Tint Paper.~--A solution of caramel in water is made of such
concentration that when diluted one hundred times (10 c.c. made up to 1
litre) the tint of this diluted solution equals the tint produced by the
Nessler test in 100 c.c. water containing .000075 grm. of ammonia, or
.00023505 grm. AmCl. With this caramel solution lines are drawn on strips
of white filter paper (previously well washed with distilled water, to