s on heating and fail to give proper colours when dried at a high
temperature.

MODERN METHODS OF JAPANNING AND ENAMELLING WITH NATURAL JAPANESE
LACQUER.

Urushiol, the principal constituent of Japanese lacquer, does not
according to the Japanese investigator, Kisaburo Miryama, dry by
itself at ordinary temperatures, but can be dried with ease at a
temperature above 96 deg. C. In the same way, lacquer that has been
heated to a temperature above 70 deg. C. and has entirely lost its drying
quality can be easily dried at a high temperature. In this method of
japanning the higher the temperature is, the more rapidly does the
drying take place; for instance, a thin layer of urushiol, or lacquer,
hardens within 5 hours at 100 deg. C., within 30 minutes at 150 deg. C., and
within 10 minutes at 180 deg. C. Japanning at a high temperature with
natural lacquer does not require the presence of the enzymic
nitrogenous matter in the lacquer, and gives a transparent coating
which is quite hard and resistant to chemical and mechanical action;
in these respects it is distinguished from that dried at an ordinary
temperature. During the drying, oxygen is absorbed from the atmosphere
and at the same time a partial decomposition takes place.

This method of japanning has its application in lacquering metal work,
glass, porcelain, earthenware, canvas, papier-mache, etc.; because the
drying is affected in a short time, and the coating thus obtained is
much more durable than the same obtained by the ordinary method.

For practical purposes it is better to _thin the lacquer with
turpentine oil or other solvent_ in order to facilitate the lacquering
and lessen the drying time of the lacquer. Since the lacquer-coating
turns brown at a high temperature, lacquers of a light colour should
be dried at 120 deg. to 150 deg. C.; and even those of a deep colour must not
be heated above 180 deg. C. _Most pigments are blackened by lacquer;
therefore the varieties of coloured lacquers are very limited._

FOOTNOTES:

[1] A question has been raised concerning the safety of
Perkins' apparatus, not merely as relates to the danger of explosion,
but also respecting that of high temperature; and it has been asserted
that the water may be so highly heated in the tubes as to endanger the
charring and even inflammation of paper, wood, and other substances in
their contact or vicinity: such no doubt might be the case in an
apparatus expressly intended for su