quill or piece of white silk into it; then wash off the acid.
What color is imparted to animal substances? (4) Add a little to
a few bits of Cu turnings, or to a Cu coin. Write the equation.
(5) To 2 cc.indigo solution, add 2 cc. HNO3. State the leading
properties of HNO3, from these tests.

87. Chemically Pure HNO3 is a Colorless Liquid.-- The yellow
color of that prepared in Experiment 52 is due to liquid NO2
dissolved in it. It is then called fuming HNO3, and is very
strong. NO2 is formed at a high temperature.

Commercial or ordinary HNO3, is made from NaNO3, this being
cheaper than KNO3; it is about half water.

88. Uses. HNO3 is the basis of many nitrates, as AgNO3, used for
photography, Ba(NO3)2 and Sr(NO3)2 for fire-works, and others for
dyeing and printing calico; it is employed in making aqua regia,
sulphuric acid, nitro-glycerine, gun-cotton, aniline colors,
zylonite, etc.

Enough experiments have been performed to answer the question
whether some acids can be prepared from their salts. H2SO4 is not
so made, because no acid is strong enough to act on its salts. In
making HCl, HNO3, etc., sulphuric acid was used, being the
strongest.

AQUA REGIA.

89. Preparation and Action. Experiment 54.--Into a t.t. put 2 cc.
HNO3, and 14 qcm. of either Au leaf or Pt. Warm in a flame. If