Eastsmithfield Londn. July 29 1763
The Skin and Cartilages must be freed as much as possible from
the other parts of the Fish and particularly from what are fat and
unctuous, let them be washed clean and then boiled gently in a
Sufficient Quantity of Water till they are disolved as much as
possible or till little remains except some very gross Parts, The
Liquor must be skimm’d pretty often, during the Coction and when it
begins to grow thick, must be kept continually stirring to prevent
burning; after wich the Decoction must be strained thro a fine
wicker basket, permitted to settle an hour or 2 and then the clear
Liquor must be evaporated in a proper Vessel till it is very thick,
when it must be pourd into proper Moulds of Wood or Tin to stiffin,
after wich it must be taken out and laid upon Netts stretchd in
Frames, to dry till it becomes hard enough for Use.
Copper Vessells for making glues are most
commodious. They must be of two kinds, One to boil the Subject in
and the Other to evaporate the superfluous Moisture; The first may
be constructed like a Brewers Copper fixed in Brick work with a
Door, Grate, &c. After the Usual Method; The Other must be a
double Vessel, or Water Bath, the outward Vessel of which, must be
likewise set in Brick Work or the evaporating Vessel may be adapted
to the Boiling Vessel wich thus may Answer two Purposes, first to
boil the Subject in and afterwards receive the other Vessel to
evaporate the Liquor, but where Dispatch in Busness is required it
will be found to most advantage to have them seperate, that one may
be boiling while the Other is evaporating; the double Vessel must
therefore be very large in Diamiter and so shallow that altho it be
large enough for its Companion to contain all the Decoction yet
need not be more than 2 feet Deep or thereabouts; The two Vessels
may be Set contiguous to each other with diffirent Flews in the
same Chimney; The Companion to this shallow Pan must be adapted in
such manner that it must be suspended within the Other by a broad
Rim of Copper rivetted to its sides 6 Inches below [its] Edge or
upper Rim, which Rim must rest upon the Edge or Top of the fixed
Copper, the inward vesel must be less in Diamitir to the other, so
as to leave 3 inches Space between the sides of the Two Vessels,
every where around when the inner Vessel is suspended and 4 Inches
Space from the bottom; At the Distance of every Foot in the Rim may
be cut vent Holes, about Three Inches Long and two Inches Wide to
let out the Steam of the boiling water in the outward Vessel; That
Part of the inward Vessel above the Rim may be 6 or 8 inches that
it may contain the more Matter to be evaporated, and be more
readily taken out occasionally.
After the Glutinous Subjects have been disolved
[word missing] slow continued boiling with repeated
Quantities of water in the boiling Vessel; The Decoctions must be
strained, permitted to subside in wooden Casks or tubs drawn off
pretty Clear and put into the evaporating-vessel, previously
suspended in the Other already filled 2 thirds with Water; The Fire
must then be kept up, so as to keep the water round the inner vesel
in a continued boiling State which water must be supply’d
Occasionally as it wastes and the Decoction stir’d frequently till
all the superfluous Moisture is evaporated and the Magma becomes
just thin enough to pour into the moulds very slightly greased to
prevent its sticking; In this state it must dry till it is stiff
enough to lay upon Netts to be further dried for use; The Tin Pans
need only to be made of a Sheet of tin, 6 or 8 inches Square, with
the Edges turned up equal to the intended Thickness of the Glue
Cake. The Nett Frames for drying resemble a little Hutt, They may
be about eight Feet long as many high and Four wide, fixed about 6
inches distance from each other and one over another from the
Ground to the Eaves of the Roof, wich Roof is weather boarded, the
Hutt with its Roof must be built first, and the Frame with the
Netts fastned within it afterwards; Thus the Netts will be open on
all sides to the Air except the Top wich Defends them from Rain,
the great Dificulty in making Glue is to prevent its burning which
is effectualy done by this Method as the Decotion can receive no
greater heat than [the] boiling water; The evaporating Pan is made
broad and Shallow because all evaporations is in proportion to
Surface exposed to the Air, Common Glue is generally of a brown
Colour being generally a little burnt and full of heterogene
particles, but Glue made after this Process will be the most
perfect that can Possibly be made and will when finished appear
tranparant and of a grenish Hue, it is the strongest that can be
made and grows so hard between Timber as to resist moisture
incredibly. Size is only Glue left in the Consist[ency] between
Jelly and Glue, and Jellys are only thin Size, Papins Machine will
disolve Animal Substance more readily, but is Inapplicable in a
large way. Iron or Copper Ladles will be nessesasary to lade out
the Glue; I know of nothing more worth describing but what will
naturally occur to the Practitioner.