be burnt off. A white ash will indicate the
presence of alumina mordants, red ash that of iron mordants, and a
greenish ash chrome mordants.

To confirm these the following chemical tests may be applied: Boil the
ash left in the crucible with a little strong hydrochloric acid and
dilute with water. Pass a current of sulphuretted hydrogen gas through
the solution; if there be any tin present a brown precipitate of tin
sulphide will be obtained. This can be filtered off. The filtrate is
boiled for a short time with nitric acid, and ammonia is added to the
solution when alumina is thrown down as a white gelatinous precipitate;
iron is thrown down as a brown red bulky precipitate; while chrome is
thrown down as a greyish-looking gelatinous precipitate. The precipitate
obtained with the ammonia is filtered off, and a drop of ammonium
sulphide added, when any zinc present will be thrown down as white
precipitate of zinc sulphide: to the filtrate from this ammonium oxalate
may be added, when if lime is present a white precipitate of calcium
oxalate is obtained.

A test for iron is to dissolve some of the ash in a little hydrochloric
acid, and add a few drops of potassium ferrocyanide solution, when if
any iron be present a blue precipitate will be obtained.

To make more certain of the presence of chrome, heat a little of the ash
of the cloth with caustic soda and chlorate of soda in a porcelain
crucible until well fused, then dissolve in water, acidify with acetic
acid and add lead acetate; a yellow precipitate indicates the presence
of chrome.

A book on qualitative chemical analysis should be referred to for
further details and tests for metallic mordants.

The fastness of colours to light, air, rubbing, washing, soaping, acids
and alkalies is a feature of some considerable importance. There are
indeed few colours that will resist all these influences, and such are
fully entitled to be called fast. The decree of fastness varies very
considerably. Some colours will resist acids and alkalies well, but are
not fast to light and air; some will resist washing and soaping, but are
not fast to acids; Some may be fast to light, but are not so to washing.
The following notes will show how to test these features:--

=Fastness to Light and Air.=--This is simply tested by hanging a piece
of the dyed cloth in the air, keeping a piece in a drawer to refer to,
so that the influence on the original colour can be noted from time to
t