GELATINE SIZE 293
paper while it is passing through the tub, and then dry hard on the dryer after-
wards, giving the maximum resistance to ink and moisture and the maximum
increase in strength and bursting strain. When testing gelatines, the colour
of the solution must be taken into account, because the use of dark-coloured
solutions will bring^ down the colour of the paper to an appreciable extent.
A rough way of testing samples against each other is to weigh out pieces
according to their price; soak in water for 24 hours, remove them and wipe
off surplus moisture, and then dissolve in equal quantities of water in a water-
bath. When all the jelly has dissolved, remove the dish from the water-bath
and allow to stand until cold. The srifFest jelly will be the most economical,
and, if its colour is satisfactory, will be the best for tub-sizing.
The stock solution of size is made in the following way: The sheets are
placed in a tank, covered with cold water and allowed to stand for 24 hours.
By this time they will have swollen to several times their original thickness,
but they will not have dissolved. The water may be drained off and hot water
added, or the temperature of the water in the tank may be raised to about
150° F. The jelly will dissolve, and soap may be added in the proportion of
about 2 or 3 per cent on the dry weight of gelatine. When the soap has dissolved,
12 to 14 per cent of alum is added, and the size is now ready to be run to the
store tanks. Here it is tested for strength, and if too.strong it is diluted with
hot water to the required strength. It is now ready for use.
The tub-sizing machine consists of a trough, either of wood, lined with lead
or copper, or of cast iron with a copper lining. No iron- or steel-work must
come in contact with the gelatine solution.
The trough is heated by a copper steam coil or may have a double bottom
with hot water circulating across the under side, in order that the temperature
of the size may be kept constant. The best method is undoubtedly that in
which hot water circulates through the bottom of the entire tub, as in this
way the whole of the solution is kept at a uniform temperature. The tem-
perature of the size is indicated by a thermometer kept permanently in the tub.
A thermostatic controller will give perfect results.
Various methods are used for leading the web of paper through the tub,
and all paper-makers seem to have their own ideas about it. The main principles
to be borne in mind, however, are that the paper should be soaked for a period
sufficient to allow it to expand to the utmost, otherwise trouble will be experi-
enced with ribbing or piping of the paper as it is wound up wet after leaving
the tub. This ribbing is caused by the paper still taking in size and expanding
while being tightly wound, and as it cannot expand easily outwards, it expands
upwards and takes on a shape resembling that of corrugated iron.
A suitable arrangement of squeezing rolls must be fixed at the end of the