(NH_{4})_{2}CO_{3} = NH_{4}HCO_{3} + NH_{3}.

The acid carbonate, or bicarbonate, is prepared by saturating a solution
of ammonium hydroxide with carbon dioxide:

NH_{4}OH + CO_{2} = NH_{4}HCO_{3}.

It is a well-crystallized stable substance.

~Ammonium sulphide~ ((NH_{4})_{2}S). Ammonium sulphide is prepared by the
action of hydrosulphuric acid upon ammonium hydroxide:

2NH_{4}OH + H_{2}S = (NH_{4})_{2}S + 2H_{2}O.

If the action is allowed to continue until no more hydrosulphuric acid
is absorbed, the product is the acid sulphide, sometimes called the
hydrosulphide:

NH_{4}OH + H_{2}S = NH_{4}HS + H_{2}O.

If equal amounts of ammonium hydroxide and ammonium acid sulphide are
brought together, the normal sulphide is formed:

NH_{4}OH + NH_{4}HS = (NH_{4})_{2}S + H_{2}O

It has been obtained in the solid state, but only with great difficulty.
As used in the laboratory it is always in the form of a solution. It is
much used in the process of chemical analysis because it is a soluble
sulphide and easily prepared. On exposure to the air ammonium sulphide
slowly decomposes, being converted into ammonia, water, and sulphur:

(NH_{4})_{2}S + O = 2NH_{3} + H_{2}O + S.

As fast as the sulphur is liberated it combines with the unchanged
sulphide to form several different ammonium sulphides in which there are
from two to five sulphur atoms in the molecule, thus: (NH_{4})_{2}S_{2},
(NH_{4})_{2}S_{3}, (NH_{4})_{2}S_{5}. These sulphides in turn decompose
by further action of oxygen, so that the final products of the reaction
are those given in the equation. A solution of these compounds is yellow
and is sometimes called _yellow ammonium sulphide_.

FLAME REACTION--SPECTROSCOPE

When compounds of either sodium or potassium are brought into
the non-luminous flame of a Bunsen burner the flame becomes
colored. Sodium compounds color it intensely yellow, while
those of potassium color it pale violet. When only one of these
elements is present it is easy to identify it by this simple
test, but when both are present the intense color of the sodium
flame entirely conceals the pale tint characteristic of
potassium compounds.

It is possible to detect the potassium flame in such cases,
however, in the following way. When light is allowed to shine
through a very small hole or slit in some kind of a screen,
such as a piece of metal, upon