0-1/2 inches broad and 6-1/2 inches
deep--this is covered by a lid in which are six apertures to take the
porcelain dye-baths. The bath is heated by two round gas boiling burners
of the type already referred to.

The copper bath is filled with water, which, on being heated to the boil
by the gas burners, heats up the dye liquids in the dye-pots. The
temperature in the dye-pots under such conditions can never reach the
boiling point; where it is desirable, as in some cases of wool
mordanting and dyeing, that it should boil, there should be added to the
water in the copper bath a quantity of calcium chloride, which forms a
solution that has a much higher boiling point than that of water, and so
the dye liquors in the dye-pots may be heated up to the boil.

An objection might be raised that with such an apparatus the temperature
in every part of the bath may not be uniform, and so the temperature of
the dye-liquors in the pots may vary also, and differences of
temperature often have a considerable influence on the shade of the
colour which is being dyed. This is a minor objection, which is more
academic in its origin than of practical importance. To obviate this Mr.
William Marshall of the Rochdale Technical School has devised a circular
form of dye-bath, in which the temperature in every part can be kept
quite uniform.

The dyeing laboratories of technical schools and colleges are generally
provided with a more elaborate set of dyeing appliances. These, in the
latest constructed, consist of a copper bath supported on a hollow pair
of trunnions, that the bath can be turned over if needed. Into the bath
are firmly fixed three earthenware or porcelain dye-pots; steam for
heating can be sent through the trunnions. After the dyeing tests have
been made the apparatus can be turned over, and the contents of the
dye-pots emptied into a sink which is provided for the purpose.

Many other pieces of apparatus have been devised and made for the
purpose of carrying on dyeing experiments on the small scale, but it
will not be needful to describe these in detail. After all no more
efficient apparatus can be desired than that described above.

Dyeing experiments can be made with either yarns or pieces of
cloth--swatches, as they are commonly called--a very convenient size is
a small skein of yarn or a piece of cloth having a weight of 5 grams.
These test skeins or pieces ought to be well washed in hot water before
use, so that they