Enamels and enamelling; an introduction to the preparation and ...

50 ENAMELS AND ENAMELLING.
Antimony Oxide.
This oxide may be prepared by the wet or dry method.
In the former case, finely powdered metallic antimony is
placed in a glass vessel (standing in a basin of water) and
treated with nitric acid of a certain strength. The acid
rapidly attacks the metal and converts it into a white powder,
reddish-brown fumes being evolved. Owing to the violence
of the reaction, the acid must be added in small quantities at a
time or the contents of the flask will overflow, even when the
latter is comparatively large.
Towards the close, the reaction
abates and may then be assisted by carefully heating the
water bath in which the flask is immersed.
To obtain a product of well-defined properties it is neces-
in accordance with the instructions now
sary to work precisely
The following quantities, viz. :
given.
Powdered antimony
1 part by weight.
Nitric acid (sp. gr. 1-2) 4 parts ,,
Water 8
are taken, and the ensuing product (the Stibium oxydatum
grisum of the pharmacist) must be thoroughly
hot water and weighed ;
washed with
it is, however, not quite pure, as it
.always contains small quantities of unaltered metal and basic
antimony nitrate. Nevertheless, as the proportion of these
impurities will always be constant, provided the above condi-
tions are adhered to in making the preparation, it will be easy,
by means of a few tests, to produce well-defined shades of
yellow with this material. The washing
in hot water is an
important feature, and must be continued until the liquid
ceases to take up any portion of the precipitate into solution.
When metallic antimony is heated in an inclined crucible
it quickly fuses and, when the heat is increased, takes fire,
this effect being accelerated by blowing air into the crucible.
The combustion is accompanied by a peculiar bluish flame and
dense white fumes of antimony oxide are given off. These